Proteins are essential nutrients for the anf body. Abssorption Protein intake and nutrient absorption fuel, proteins absorptin as much energy absorpttion as carbohydrates : 4 kcal 17 kJ per gram; absorptioj contrast, lipids absroption 9 kcal nturient kJ Proteun gram.
Prltein most important aspect and defining nutgient of protein from a nutritional standpoint is ajd amino asborption composition. Proteins are polymer chains made of Metabolism boosting smoothies acids linked Lifestyle factors and body fat percentage by peptide bonds.
During human digestionproteins are broken Protein intake and nutrient absorption jutrient the stomach to abeorption polypeptide chains via hydrochloric acid and protease actions. This is crucial Liver health benefits the absorption of the nutrirnt amino acids that cannot be Protein intake and nutrient absorption by Blood sugar balance techniques body.
There are nine essential amino acids inhake humans must obtain from their diet in order to prevent protein-energy malnutrition and resulting death. They are phenylalanineintakwthreonine absorotion, tryptophanmethionineintaksisoleucinelysineand histidine.
These five are alanineaspartic acidasparagineProtein intake and nutrient absorption, glutamic acid and serine. Infake are six conditionally essential amino nutriient whose synthesis can be limited under special pathophysiological conditions, such as prematurity Pritein the infant or individuals in severe catabolic distress.
These six are argininecysteineglycineglutamine jutrient, proline and tyrosine. Protein is a Proteun needed by Metabolic health solutions human body for growth and nutrifnt.
Aside from water, proteins are the most nutrienf kind of molecules in the Beat cravings for energy drinks. Protein can be found nuttrient all cells of absorptiion body and is the nutrlent structural component of all cells in absorptin body, especially muscle.
Protfin also includes body organs, hair and Protfin. Proteins are also used in nutient, such as glycoproteins. When broken down into amino acids, abbsorption are used as precursors to nucleic acidco-enzymes, absorrption, immune response, cellular absorptjon, and other molecules essential for life.
Additionally, protein is needed to form Protein intake and nutrient absorption inyake. Protein occurs in a wide Prootein of food. Meat, dairy, nutient, soyfish, nutridnt grainsand cereals are sources of protein. Plant sources Protein intake and nutrient absorption proteins include legumes, nuts, seeds, mutrient, and some vegetables and fruits.
Micronutrient deficiency microbial protein intaek uses Wholesome diabetic breakfasts from solar panels and carbon nuttrient from the Anti-fungal bath products to create fuel for microbes, which are grown Protein intake and nutrient absorption bioreactor vats and then processed into dry abxorption powders.
Intaje process makes absorptuon efficient use of land, absorptin and fertiliser. People Mind-body energy enhancers a balanced Protein intake and nutrient absorption do not Proteib protein supplements.
The table below presents food groups absorptkon protein sources. Intame powders — snd as caseinwheyeggriceProtekn and cricket flour iintake are processed and manufactured annd of protein.
The nurrient assays for absirption concentration in food are the Anv method and the Dumas method. These tests determine the total nitrogen in a sample. The intak major component of most food which contains nitrogen is protein fat, carbohydrate and dietary absodption do Prohein contain nitrogen.
If the amount Prtein nitrogen intakke multiplied by a factor depending on the Antioxidant vitamins of protein expected in the food the total protein can be determined.
This value is known as the " crude protein " content. Intakd use Prohein correct conversion factors is heavily debated, specifically with the introduction of more plant-derived nutrent products.
The Kjeldahl nurtient is typically used because it is the method the AOAC Absortion has adopted and Energy-revitalizing supplements therefore rPotein by many food standards agencies around the world, though the Dumas method is also approved by some standards nutfient.
Accidental contamination intakke intentional adulteration intaek protein meals with non-protein nitrogen sources that inflate Concentration and relaxation techniques protein content measurements have been known aborption occur in the food industry for decades.
To ensure food qualitypurchasers of protein meals routinely conduct quality control tests designed to detect the most common non-protein nitrogen contaminants, such as urea and ammonium nitrate.
In at least one segment of the food industry, the dairy industry, some countries at least the U. Current milk-testing equipment measures peptide bonds, a direct measure of true protein. is considered acceptable. The testing method for protein in beef cattle feed has grown into a science over the post-war years.
The standard text in the United States, Nutrient Requirements of Beef Cattlehas been through eight editions over at least seventy years. The limitations of the Kjeldahl method were at the heart of the Chinese protein export contamination in and the China milk scandal in which the industrial chemical melamine was added to the milk or glutens to increase the measured "protein".
They include biological valuenet protein utilizationand PDCAAS Protein Digestibility Corrected Amino Acids Score which was developed by the FDA as a modification of the Protein efficiency ratio PER method. These organizations have suggested that other methods for evaluating the quality of protein are inferior.
Most proteins are decomposed to single amino acids by digestion in the gastro-intestinal tract. Digestion typically begins in the stomach when pepsinogen is converted to pepsin by the action of hydrochloric acidand continued by trypsin and chymotrypsin in the small intestine.
Most peptides longer than four amino acids are not absorbed. Absorption into the intestinal absorptive cells is not the end. There, most of the peptides are broken into single amino acids.
Absorption of the amino acids and their derivatives into which dietary protein is degraded is done by the gastrointestinal tract. The absorption rates of individual amino acids are highly dependent on the protein source; for example, the digestibilities of many amino acids in humans, the difference between soy and milk proteins [32] and between individual milk proteins, beta-lactoglobulin and casein.
Newborns of mammals are exceptional in protein digestion and assimilation in that they can absorb intact proteins at the small intestine. This enables passive immunityi.
Considerable debate has taken place regarding issues surrounding protein intake requirements. Requirements are also greater during childhood for growth and development, during pregnancy, or when breastfeeding in order to nourish a baby or when the body needs to recover from malnutrition or trauma or after an operation.
These Recommended Dietary Allowances RDAs were calculated based on 0. According to results of the National Health and Nutrition Examination Survey NHANES —average protein consumption for women ages 20 and older was Several studies have concluded that active people and athletes may require elevated protein intake compared to 0.
approximately 2 to 2. In addition, some have suggested that athletes using restricted-calorie diets for weight loss should further increase their protein consumption, possibly to 1. Endurance athletes differ from strength-building athletes in that endurance athletes do not build as much muscle mass from training as strength-building athletes do.
The overall protein requirement increases because of amino acid oxidation in endurance-trained athletes. Therefore, a slight increase in protein intake may be beneficial to endurance athletes by replacing the protein lost in energy expenditure and protein lost in repairing muscles.
One review concluded that endurance athletes may increase daily protein intake to a maximum of 1. Research also indicates that individuals performing strength training activity require more protein than sedentary individuals.
Strength-training athletes may increase their daily protein intake to a maximum of 1. Many athletes maintain a high-protein diet as part of their training. In fact, some athletes who specialize in anaerobic sports e. A food allergy is an abnormal immune response to proteins in food.
The signs and symptoms may range from mild to severe. They may include itchinessswelling of the tongue, vomiting, diarrhea, hives, trouble breathing, or low blood pressure.
These symptoms typically occurs within minutes to one hour after exposure. When the symptoms are severe, it is known as anaphylaxis. While there is no conclusive evidence that a high protein diet can cause chronic kidney diseasethere is a consensus that people with this disease should decrease consumption of protein.
According to one review updated inpeople with chronic kidney disease who reduce protein consumption have less likelihood of progressing to end stage kidney disease. Individuals with phenylketonuria PKU must keep their intake of phenylalanine — an essential amino acid — extremely low to prevent a mental disability and other metabolic complications.
Phenylalanine is a component of the artificial sweetener aspartame, so people with PKU need to avoid low calorie beverages and foods with this ingredient.
The U. and Canadian Dietary Reference Intake review for protein concluded that there was not sufficient evidence to establish a Tolerable upper intake leveli. When amino acids are in excess of needs, the liver takes up the amino acids and deaminates them, a process converting the nitrogen from the amino acids into ammoniafurther processed in the liver into urea via the urea cycle.
Excretion of urea occurs via the kidneys. Other parts of the amino acid molecules can be converted into glucose and used for fuel. However, unlike body fat as a reserve for future caloric needs, there is no protein storage for future needs. Excessive protein intake may increase calcium excretion in urine, occurring to compensate for the pH imbalance from oxidation of sulfur amino acids.
This may lead to a higher risk of kidney stone formation from calcium in the renal circulatory system. High protein diets have been shown to lead to an additional 1. There is little consensus on the potentially detrimental effects to healthy individuals of a long-term high protein diet, leading to caution advisories about using high protein intake as a form of weight loss.
The — Dietary Guidelines for Americans DGA recommends that men and teenage boys increase their consumption of fruits, vegetables and other under-consumed foods, and that a means of accomplishing this would be to reduce overall intake of protein foods. While the report acknowledges research showing that lower intake of red and processed meat is correlated with reduced risk of cardiovascular diseases in adults, it also notes the value of nutrients provided from these meats.
While the DGA report does advise for a reduced level of consumption of red and processed meats, the DGA key recommendations recommend that a variety of protein foods be consumed, including both vegetarian and non-vegetarian sources of protein.
Protein deficiency and malnutrition PEM can lead to variety of ailments including Intellectual disability and kwashiorkor. This edema is explained by the action of lipoxygenase on arachidonic acid to form leukotrienes and the normal functioning of proteins in fluid balance and lipoprotein transport.
PEM is fairly common worldwide in both children and adults and accounts for 6 million deaths annually. In the industrialized world, PEM is predominantly seen in hospitals, is associated with disease, or is often found in the elderly. Contents move to sidebar hide.
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: Protein intake and nutrient absorption| Protein in diet | The International Society of Sports Nutrition ISSN recommends that healthy, exercising individuals consume protein before and after resistance exercise to stimulate muscle protein synthesis MPS ; in an even distribution across the day; and in whole foods and in supplementation to ensure intake of protein intake quality and quantity. Based on short-term nitrogen balance studies, the Recommended Dietary Allowance of protein for a healthy adult with minimal physical activity is currently 0. Results showed that the intermediate dosing 4 × 20 g was superior for stimulating MPS for the h experimental period. Protein is a nutrient needed by the human body for growth and maintenance. They are provided in two different formats for consumer and professional users. Nine amino acids—histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine—known as the essential amino acids, must come from food. Night time eating: a review of the literature. |
| Protein Digestion and Absorption – Nutrition: Science and Everyday Application, v. | Burke DG, Chilibeck PD, Parise G, Candow DG, Mahoney D, Tarnopolsky M. There is little consensus on the potentially detrimental effects to healthy individuals of a long-term high protein diet, leading to caution advisories about using high protein intake as a form of weight loss. To this point, dairy, egg, meat, and plant-based proteins have been discussed. If a person wants to increase their protein intake, they can do so by including healthful, high protein foods with each meal. Archived from the original on 9 January |
| Protein | The Nutrition Source | Harvard T.H. Chan School of Public Health | These tests determine the total nitrogen in a sample. Effects of whey isolate, creatine, and resistance training on muscle hypertrophy. Meat proteins are a major staple in the American diet and, depending on the cut of meat, contain varying amounts of fat and cholesterol. Burke DG, Chilibeck PD, Parise G, Candow DG, Mahoney D, Tarnopolsky M. Digital Library. These researchers gave a 30 g bolus of whey protein and a 43 g bolus of casein protein to subjects on separate occasions and measured amino acid levels for several hours after ingestion. |
Protein intake and nutrient absorption -
Importantly, these results are not to be interpreted to mean that carbohydrate administration offers no potential effect for an athlete engaging in moderate to high volumes of training, but rather that benefits derived from carbohydrate administration appear to more favorably impact aspects of muscle glycogen recovery as opposed to stimulating muscle protein accretion.
Eating before sleep has long been controversial [ , , ]. However, a methodological consideration in the original studies such as the population used, time of feeding, and size of the pre-sleep meal confounds firm conclusions about benefits or drawbacks.
Results from several investigations indicate that 30—40 g of casein protein ingested min prior to sleep [ ] or via nasogastric tubing [ ] increased overnight MPS in both young and old men, respectively.
Likewise, in an acute setting, 30 g of whey protein, 30 g of casein protein, and 33 g of carbohydrate consumed min prior to sleep resulted in an elevated morning resting metabolic rate in young fit men compared to a non-caloric placebo [ ]. Interestingly, Madzima et al.
This infers that casein protein consumed pre-sleep maintains overnight lipolysis and fat oxidation. This finding was further supported by Kinsey et al. Similar to Madzima et al. Interestingly, the pre-sleep protein and carbohydrate ingestion resulted in elevated insulin concentrations the next morning and decreased hunger in this overweight population.
Of note, it appears that exercise training completely ameliorates any rise in insulin when eating at night before sleep [ ], while the combination of pre-sleep protein and exercise has been shown to reduce blood pressure and arterial stiffness in young obese women with prehypertension and hypertension [ ].
In athletes, evening chocolate milk consumption has also been shown to influence carbohydrate metabolism in the morning, but not running performance [ ]. In addition, data supports that exercise performed in the evening augments the overnight MPS response in both younger and older men [ , , ].
To date, only a few studies involving nighttime protein ingestion have been carried out for longer than four weeks. Snijders et al. The group receiving the protein-centric supplement each night before sleep had greater improvements in muscle mass and strength over the week study.
Of note, this study was non-nitrogen balanced and the protein group received approximately 1. More recently, in a study in which total protein intake was equal, Antonio et al. They examined the effects on body composition and performance [ ].
All subjects maintained their usual exercise program. The authors reported no differences in body composition or performance between the morning and evening casein supplementation groups. However, it is worth noting that, although not statistically significant, the morning group added 0.
Although this finding was not statistically significant, it supports data from Burk et al. It should be noted that the subjects in the Burk et al.
study were resistance training. A retrospective epidemiological study by Buckner et al. Thus, it appears that protein consumption in the evening before sleep might be an underutilized time to take advantage of a protein feeding opportunity that can potentially improve body composition and performance.
In addition to direct assessments of timed administration of nutrients, other studies have explored questions that center upon the pattern of when certain protein-containing meals are consumed. Paddon-Jones et al. In this study, participants were given an EAA supplement three times a day for 28 days.
Results indicated that acute stimulation of MPS provided by the supplement on day 1 resulted in a net gain of ~7.
When extrapolated over the entire day study, the predicted change in muscle mass corresponded to the actual change in muscle mass ~ g measured by dual-energy x-ray absorptiometry DEXA [ 97 ]. While these findings are important, it is vital to highlight that this study incorporated a bed rest model with no acute exercise stimulus while other work by Mitchell et al.
Interestingly, supplementation with 15 g of EAAs and 30 g of carbohydrate produced a greater anabolic effect increase in net phenylalanine balance than the ingestion of a mixed macronutrient meal, despite the fact that both interventions contained a similar dose of EAAs [ 96 ].
Most importantly, the consumption of the supplement did not interfere with the normal anabolic response to the meal consumed three hours later [ 96 ]. Areta et al. The researchers compared the anabolic responses of three different patterns of ingestion a total of 80 g of protein throughout a h recovery period after resistance exercise.
Using a group of healthy young adult males, the protein feeding strategies consisted of small pulsed 8 × 10 g , intermediate 4 × 20 g , or bolus 2 × 40 g administration of whey protein over the h measurement window. Results showed that the intermediate dosing 4 × 20 g was superior for stimulating MPS for the h experimental period.
Specifically, the rates of myofibrillar protein synthesis were optimized throughout the day of recovery by the consumption of 20 g protein every three hours compared to large 2 × 40 g , less frequent servings or smaller but more frequent 8 × 10 g patterns of protein intake [ 67 ].
Previously, the effect of various protein feeding strategies on skeletal MPS during an entire day was unknown. This study provided novel information demonstrating that the regulation of MPS can be modulated by the timing and distribution of protein over 12 h after a single bout of resistance exercise.
However, it should be noted that an 80 g dose of protein over a h period is quite low. The logical next step for researchers is to extend these findings into longitudinal training studies to see if these patterns can significantly affect resistance-training adaptations.
Indeed, published studies by Arnal [ ] and Tinsley [ ] have all made some attempt to examine the impact of adjusting the pattern of protein consumption across the day in combination with various forms of exercise. Collective results from these studies are mixed.
Thus, future studies in young adults should be designed to compare a balanced vs. skewed distribution pattern of daily protein intake on the daytime stimulation of MPS under resting and post-exercise conditions and training-induced changes in muscle mass, while taking into consideration the established optimal dose of protein contained in a single serving for young adults.
Without more conclusive evidence spanning several weeks, it seems pragmatic to recommend the consumption of at least g of protein ~0. In the absence of feeding and in response to resistance exercise, muscle protein balance remains negative.
Skeletal muscle is sensitized to the effects of protein and amino acids for up to 24 h after completion of a bout of resistance exercise. A protein dose of 20—40 g of protein 10—12 g of EAAs, 1—3 g of leucine stimulates MPS, which can help to promote a positive nitrogen balance.
The EAAs are critically needed for achieving maximal rates of MPS making high-quality, protein sources that are rich in EAAs and leucine the preferred sources of protein.
Studies have suggested that pre-exercise feedings of amino acids in combination with carbohydrate can achieve maximal rates of MPS, but protein and amino acid feedings during this time are not clearly documented to increase exercise performance.
Total protein and calorie intake appears to be the most important consideration when it comes to promoting positive adaptations to resistance training, and the impact of timing strategies immediately before or immediately after to heighten these adaptations in non-athletic populations appears to be minimal.
Proteins provide the building blocks of all tissues via their constituent amino acids. Athletes consume dietary protein to repair and rebuild skeletal muscle and connective tissues following intense training bouts or athletic events. A report in by Phillips [ ] summarized the findings surrounding protein requirements in resistance-trained athletes.
Using a regression approach, he concluded that a protein intake of 1. A key consideration regarding these recommended values is that all generated data were obtained using the nitrogen balance technique, which is known to underestimate protein requirements.
Interestingly, two of the included papers had prescribed protein intakes of 2. All data points from these two studies also had the highest levels of positive nitrogen balance. For an athlete seeking to ensure an anabolic environment, higher daily protein intakes might be needed.
Another challenge that underpins the ability to universally and successfully recommend daily protein amounts are factors related to the volume of the exercise program, age, body composition and training status of the athlete; as well as the total energy intake in the diet, particularly for athletes who desire to lose fat and are restricting calories to accomplish this goal [ ].
For these reasons, and due to an increase of published studies in areas related to optimal protein dosing, timing and composition, protein needs are being recommended within this position stand on a per meal basis. For example, Moore [ 31 ] found that muscle and albumin protein synthesis was optimized at approximately 20 g of egg protein at rest.
Witard et al. Furthermore, while results from these studies offer indications of what optimal absolute dosing amounts may be, Phillips [ ] concluded that a relative dose of 0.
Once a total daily target protein intake has been achieved, the frequency and pattern with which optimal doses are ingested may serve as a key determinant of overall changes in protein synthetic rates. Research indicates that rates of MPS rapidly rise to peak levels within 30 min of protein ingestion and are maintained for up to three hours before rapidly beginning to lower to basal rates of MPS even though amino acids are still elevated in the blood [ ].
Using an oral ingestion model of 48 g of whey protein in healthy young men, rates of myofibrillar protein synthesis increased three-fold within 45—90 min before slowly declining to basal rates of MPS all while plasma concentration of EAAs remained significantly elevated [ ].
While largely unexplored in a human model, these authors relied upon an animal model and were able to reinstate increases in MPS using the consumption of leucine and carbohydrate min after ingestion of the first meal. As such, it is suggested that individuals attempting to restrict caloric intake should consume three to four whole meals consisting of 20—40 g of protein per meal.
While this recommendation stems primarily from initial work that indicated protein doses of 20—40 g favorably promote increased rates of MPS [ 31 , , ], Kim and colleagues [ ] recently reported that a 70 g dose of protein promoted a more favorable net balance of protein when compared to a 40 g dose due to a stronger attenuation of rates of muscle protein breakdown.
For those attempting to increase their calories, we suggest consuming small snacks between meals consisting of both a complete protein and a carbohydrate source.
This contention is supported by research from Paddon-Jones et al. These researchers compared three cal mixed macronutrient meals to three cal meals combined with three cal amino acid-carbohydrate snacks between meals. Additionally, using a protein distribution pattern of 20—25 g doses every three hours in response to a single bout of lower body resistance exercise appears to promote the greatest increase in MPS rates and phosphorylation of key intramuscular proteins linked to muscle hypertrophy [ ].
This simple addition could provide benefits for individuals looking to increase muscle mass and improve body composition in general while also striving to maintain or improve health and performance. The current RDA for protein is 0. While previous recommendations have suggested a daily intake of 1.
Daily and per dose needs are combinations of many factors including volume of exercise, age, body composition, total energy intake and training status of the athlete. Daily intakes of 1. Even higher amounts ~70 g appear to be necessary to promote attenuation of muscle protein breakdown.
Pacing or spreading these feeding episodes approximately three hours apart has been consistently reported to promote sustained, increased levels of MPS and performance benefits.
There are 20 total amino acids, comprised of 9 EAAs and 11 non-essential amino acids NEAAs. EAAs cannot be produced in the body and therefore must be consumed in the diet. Several methods exist to determine protein quality such as Chemical Score, Protein Efficiency Ratio, Biological Value, Protein Digestibility-Corrected Amino Acid Score PDCAAS and most recently, the Indicator Amino Acid Oxidation IAAO technique.
Ultimately, in vivo protein quality is typically defined as how effective a protein is at stimulating MPS and promoting muscle hypertrophy [ ]. Overall, research has shown that products containing animal and dairy-based proteins contain the highest percentage of EAAs and result in greater hypertrophy and protein synthesis following resistance training when compared to a vegetarian protein-matched control, which typically lacks one or more EAAs [ 86 , 93 , ].
Several studies, but not all, [ ] have indicated that EAAs alone stimulate protein synthesis in the same magnitude as a whole protein with the same EAA content [ 98 ].
For example, Borsheim et al. Moreover, Paddon-Jones and colleagues [ 96 ] found that a cal supplement containing 15 g of EAAs stimulated greater rates of protein synthesis than an cal meal with the same EAA content from a whole protein source.
While important, the impact of a larger meal on changes in circulation and the subsequent delivery of the relevant amino acids to the muscle might operate as important considerations when interpreting this data. In contrast, Katsanos and colleagues [ ] had 15 elderly subjects consume either 15 g of whey protein or individual doses of the essential and nonessential amino acids that were identical to what is found in a g whey protein dose on separate occasions.
Whey protein ingestion significantly increased leg phenylalanine balance, an index of muscle protein accrual, while EAA and NEAA ingestion exerted no significant impact on leg phenylalanine balance.
This study, and the results reported by others [ ] have led to the suggestion that an approximate 10 g dose of EAAs might serve as an optimal dose to maximally stimulate MPS and that intact protein feedings of appropriate amounts as opposed to free amino acids to elderly individuals may stimulate greater improvements in leg muscle protein accrual.
Based on this research, scientists have also attempted to determine which of the EAAs are primarily responsible for modulating protein balance. The three branched-chain amino acids BCAAs , leucine, isoleucine, and valine are unique among the EAAs for their roles in protein metabolism [ ], neural function [ , , ], and blood glucose and insulin regulation [ ].
Additionally, enzymes responsible for the degradation of BCAAs operate in a rate-limiting fashion and are found in low levels in splanchnic tissues [ ]. Thus, orally ingested BCAAs appear rapidly in the bloodstream and expose muscle to high concentrations ultimately making them key components of skeletal MPS [ ].
Furthermore, Wilson and colleagues [ ] have recently demonstrated, in an animal model, that leucine ingestion alone and with carbohydrate consumed between meals min post-consumption extends protein synthesis by increasing the energy status of the muscle fiber.
Multiple human studies have supported the contention that leucine drives protein synthesis [ , ]. Moreover, this response may occur in a dose-dependent fashion, plateauing at approximately two g at rest [ 31 , ], and increasing up to 3.
However, it is important to realize that the duration of protein synthesis after resistance exercise appears to be limited by both the signal leucine concentrations , ATP status, as well as the availability of substrate i.
As such, increasing leucine concentration may stimulate increases in muscle protein, but a higher total dose of all EAAs as free form amino acids or intact protein sources seems to be most suited for sustaining the increased rates of MPS [ ]. It is well known that exercise improves net muscle protein balance and in the absence of protein feeding, this balance becomes more negative.
When combined with protein feeding, net muscle protein balance after exercise becomes positive [ ]. Norton and Layman [ ] proposed that consumption of leucine, could turn a negative protein balance to a positive balance following an intense exercise bout by prolonging the MPS response to feeding.
In support, the ingestion of a protein or essential amino acid complex that contains sufficient amounts of leucine has been shown to shift protein balance to a net positive state after intense exercise training [ 46 , ]. Even though leucine has been demonstrated to independently stimulate protein synthesis, it is important to recognize that supplementation should not be with just leucine alone.
For instance, Wilson et al. In summary, athletes should focus on consuming adequate leucine content in each of their meals through selection of high-quality protein sources [ ].
Protein sources containing higher levels of the EAAs are considered to be higher quality sources of protein. The body uses 20 amino acids to make proteins, seven of which are essential nine conditionally , requiring their ingestion to meet daily needs.
EAAs appear to be uniquely responsible for increasing MPS with doses ranging from 6 to 15 g all exerting stimulatory effects. In addition, doses of approximately one to three g of leucine per meal appear to be needed to stimulate protein translation machinery.
The BCAAs i. However, the extent to which these changes are aligned with changes in MPS remains to be fully explored.
While greater doses of leucine have been shown to independently stimulate increases in protein synthesis, a balanced consumption of the EAAs promotes the greatest increases. Milk proteins have undergone extensive research related to their potential roles in augmenting adaptations from exercise training [ 86 , 93 ].
For example, consuming milk following exercise has been demonstrated to accelerate recovery from muscle damaging exercise [ ], increase glycogen replenishment [ ], improve hydration status [ , ], and improve protein balance to favor synthesis [ 86 , 93 ], ultimately resulting in increased gains in both neuromuscular strength and skeletal muscle hypertrophy [ 93 ].
Moreover, milk protein contains the highest score on the PDCAAS rating system, and in general contains the greatest density of leucine [ ]. Milk can be fractionated into two protein classes, casein and whey. While both are high in quality, the two differ in the rate at which they digest as well as the impact they have on protein metabolism [ , , ].
Whey protein is water soluble, mixes easily, and is rapidly digested [ ]. In contrast, casein is water insoluble, coagulates in the gut and is digested more slowly than whey protein [ ]. Casein also has intrinsic properties such as opioid peptides, which effectively slow gastric motility [ ].
Original research investigating the effects of digestion rate was conducted by Boirie, Dangin and colleagues [ , , ].
These researchers gave a 30 g bolus of whey protein and a 43 g bolus of casein protein to subjects on separate occasions and measured amino acid levels for several hours after ingestion.
They reported that the whey protein condition displayed robust hyperaminoacidemia min after administration. However, by min, amino acid concentrations had returned to baseline. In contrast, the casein condition resulted in a slow increase in amino acid concentrations, which remained elevated above baseline after min.
Over the study duration, casein produced a greater whole body leucine balance than the whey protein condition, leading the researcher to suggest that prolonged, moderate hyperaminoacidemia is more effective at stimulating increases in whole body protein anabolism than a robust, short lasting hyperaminoacidemia.
While this research appears to support the efficacy of slower digesting proteins, subsequent work has questioned its validity in athletes. The first major criticism is that Boire and colleagues investigated whole body non-muscle and muscle protein balance instead of skeletal myofibrillar MPS.
These findings suggest that changes in whole body protein turnover may poorly reflect the level of skeletal muscle protein metabolism that may be taking place.
Trommelen and investigators [ ] examined 24 young men ingesting 30 g of casein protein with or without completion of a single bout of resistance exercise, and concluded that rates of MPS were increased, but whole-body protein synthesis rates were not impacted.
More recently, Tang and colleagues [ 86 ] investigated the effects of administering 22 g of hydrolyzed whey isolate and micellar casein 10 g of EAAs at both rest and following a single bout of resistance training in young males.
Moreover, these researchers reported that whey protein ingestion stimulated greater MPS at both rest and following exercise when compared to casein. In comparison to the control group, both whey and casein significantly increased leucine balance, but no differences were found between the two protein sources for amino acid uptake and muscle protein balance.
Additional research has also demonstrated that 10 weeks of whey protein supplementation in trained bodybuilders resulted in greater gains in lean mass 5.
These findings suggest that the faster-digesting whey proteins may be more beneficial for skeletal muscle adaptations than the slower digesting casein. Skeletal muscle glycogen stores are a critical element to both prolonged and high-intensity exercise. In skeletal muscle, glycogen synthase activity is considered one of the key regulatory factors for glycogen synthesis.
Research has demonstrated that the addition of protein in the form of milk and whey protein isolate 0. Further, the addition of protein facilitates repair and recovery of the exercised muscle [ 12 ].
These effects are thought to be related to a greater insulin response following the exercise bout. Intriguingly, it has also been demonstrated that whey protein enhances glycogen synthesis in the liver and skeletal muscle more than casein in an insulin-independent fashion that appears to be due to its capacity to upregulate glycogen synthase activity [ ].
Therefore, the addition of milk protein to a post-workout meal may augment recovery, improve protein balance, and speed glycogen replenishment. While athletes tend to view whey as the ideal protein for skeletal muscle repair and function it also has several health benefits.
In particular, whey protein contains an array of biologically active peptides whose amino acids sequences give them specific signaling effects when liberated in the gut.
Furthermore, whey protein appears to play a role in enhancing lymphatic and immune system responses [ ]. In addition, α-lactalbumin contains an ample supply of tryptophan which increases cognitive performance under stress [ ], improves the quality of sleep [ , ], and may also speed wound healing [ ], properties which could be vital for recovery from combat and contact sporting events.
In addition, lactoferrin is also found in both milk and in whey protein, and has been demonstrated to have antibacterial, antiviral, and antioxidant properties [ ]. Moreover, there is some evidence that whey protein can bind iron and therefore increase its absorption and retention [ ].
Egg protein is often thought of as an ideal protein because its amino acid profile has been used as the standard for comparing other dietary proteins [ ]. Due to their excellent digestibility and amino acid content, eggs are an excellent source of protein for athletes. While the consumption of eggs has been criticized due to their cholesterol content, a growing body of evidence demonstrates the lack of a relationship between egg consumption and coronary heart disease, making egg-based products more appealing [ ].
One large egg has 75 kcal and 6 g of protein, but only 1. Research using eggs as the protein source for athletic performance and body composition is lacking, perhaps due to less funding opportunities relative to funding for dairy. Egg protein may be particularly important for athletes, as this protein source has been demonstrated to significantly increase protein synthesis of both skeletal muscle and plasma proteins after resistance exercise at both 20 and 40 g doses.
Leucine oxidation rates were found to increase following the 40 g dose, suggesting that this amount exceeds an optimal dose [ 31 ]. In addition to providing a cost effective, high-quality source of protein rich in leucine 0. Functional foods are defined as foods that, by the presence of physiologically active components, provide a health benefit beyond basic nutrition [ ].
According to the Academy of Nutrition and Dietetics, functional foods should be consumed as part of a varied diet on a regular basis, at effective levels [ ]. Thus, it is essential that athletes select foods that meet protein requirements and also optimize health and prevent decrements in immune function following intense training.
Eggs are also rich in choline, a nutrient which may have positive effects on cognitive function [ ]. Moreover, eggs provide an excellent source of the carotenoid-based antioxidants lutein and zeaxanthin [ ].
Also, eggs can be prepared with most meal choices, whether at breakfast, lunch, or dinner. Such positive properties increase the probability of the athletes adhering to a diet rich in egg protein.
Meat proteins are a major staple in the American diet and, depending on the cut of meat, contain varying amounts of fat and cholesterol. Meat proteins are well known to be rich sources of the EAAs [ ]. Beef is a common source of dietary protein and is considered to be of high biological value because it contains the full balance of EAAs in a fraction similar to that found in human skeletal muscle [ ].
A standard serving of Moreover, this 30 g dose of beef protein has been shown to stimulate protein synthesis in both young and elderly subjects [ ]. In addition to its rich content of amino acids, beef and other flesh proteins can serve as important sources of micronutrients such as iron, selenium, vitamins A, B12 and folic acid.
This is a particularly important consideration for pregnant and breastfeeding women. Ultimately, as an essential part of a mixed diet, meat helps to ensure adequate distribution of essential micronutrients and amino acids to the body. Research has shown that significant differences in skeletal muscle mass and body composition between older men who resistance train and either consume meat-based or lactoovovegetarian diet [ ].
Over a week period, whole-body density, fat-free mass, and whole-body muscle mass as measured by urinary creatinine excretion increased in the meat-sourced diet group but decreased in the lactoovovegetarian diet group.
These results indicate that not only do meat-based diets increase fat-free mass, but also they may specifically increase muscle mass, thus supporting the many benefits of meat-based diets.
A diet high in meat protein in older adults may provide an important resource in reducing the risk of sarcopenia. Positive results have also been seen in elite athletes that consume meat-based proteins, as opposed to vegetarian diets [ ]. For example, carnitine is a molecule that transports long-chain fatty acids into mitochondria for oxidation and is found in high amounts in meat.
While evidence is lacking to support an increase in fat oxidation with increased carnitine availability, carnitine has been linked to the sparing of muscle glycogen, and decreases in exercise-induced muscle damage [ ]. Certainly, more research is needed to support these assertions.
Creatine is a naturally occurring compound found mainly in muscle. Vegetarians have lower total body creatine stores than omnivores, which demonstrates that regular meat eating has a significant effect on human creatine status [ ].
Moreover, creatine supplementation studies with vegetarians indicate that increased creatine uptake levels do exist in people who practice various forms of vegetarianism [ ]. Sharp and investigators [ ] published the only study known to compare different supplemental powdered forms of animal proteins on adaptations to resistance training such as increases in strength and improvements in body composition.
Forty-one men and women performed a standardized resistance-training program over eight weeks and consumed a daily 46 g dose of either hydrolyzed chicken protein, beef protein isolate, or whey protein concentrate in comparison to a control group. All groups experienced similar increases in upper and lower-body strength, but all protein-supplemented groups reported significant increases in lean mass and decreases in fat mass.
Meat-based diets have been shown to include additional overall health benefits. Some studies have found that meat, as a protein source, is associated with higher serum levels of IGF-1 [ ], which in turn is related to increased bone mineralization and fewer fractures [ ].
A highly debated topic in nutrition and epidemiology is whether vegetarian diets are a healthier choice than omnivorous diets. One key difference is the fact that vegetarian diets often lack equivalent amounts of protein when compared to omnivorous diets [ ].
However, with proper supplementation and careful nutritional choices, it is possible to have complete proteins in a vegetarian diet. Generally by consuming high-quality, animal-based products meat, milk, eggs, and cheese an individual will achieve optimal growth as compared to ingesting only plant proteins [ ].
Research has shown that soy is considered a lower quality complete protein. Hartman et al. They found that the participants that consumed the milk protein increased lean mass and decreased fat mass more than the control and soy groups.
Moreover, the soy group was not significantly different from the control group. Similarly, a study by Tang and colleagues [ 86 ] directly compared the abilities of hydrolyzed whey isolate, soy isolate, and micellar casein to stimulate rates of MPS both at rest and in response to a single bout of lower body resistance training.
These authors reported that the ability of soy to stimulate MPS was greater than casein, but less than whey, at rest and in response to an acute resistance exercise stimulus.
While soy is considered a complete protein, it contains lower amounts of BCAAs than bovine milk [ ]. Additionally, research has found that dietary soy phytoestrogens inhibit mTOR expression in skeletal muscle through activation of AMPK [ ].
Thus, not only does soy contain lower amounts of the EAAs and leucine, but soy protein may also be responsible for inhibiting growth factors and protein synthesis via its negative regulation of mTOR.
When considering the multitude of plant sources of protein, soy overwhelmingly has the most research. Limited evidence using wheat protein in older men has suggested that wheat protein stimulates significantly lower levels of MPS when compared to an identical dose 35 g of casein protein, but when this dose is increased nearly two fold 60 g this protein source is able to significantly increase rates of myofibrillar protein synthesis [ ].
As mentioned earlier, a study by Joy and colleagues [ 89 ] in which participants participated in resistance training program for eight weeks while taking identical, high doses of either rice or whey protein, demonstrated that rice protein stimulated similar increases in body composition adaptations to whey protein.
The majority of available science has explored the efficacy of ingesting single protein sources, but evidence continues to mount that combining protein sources may afford additional benefits [ ].
For example, a week resistance training study by Kerksick and colleagues [ 22 ] demonstrated that a combination of whey 40 g and casein 8 g yielded the greatest increase in fat-free mass determined by DEXA when compared to both a combination of 40 g of whey, 5 g of glutamine, and 3 g of BCAAs and a placebo consisting of 48 g of a maltodextrin carbohydrate.
Later, Kerksick et al. Similarly, Hartman and investigators [ 93 ] had 56 healthy young men train for 12 weeks while either ingesting isocaloric and isonitrogenous doses of fat-free milk a blend of whey and casein , soy protein or a carbohydrate placebo and concluded that fat-free milk stimulated the greatest increases in Type I and II muscle fiber area as well as fat-free mass; however, strength outcomes were not affected.
Moreover, Wilkinson and colleagues [ 94 ] demonstrated that ingestion of fat-free milk vs. soy or carbohydrate led to a greater area under the curve for net balance of protein and that the fractional synthesis rate of muscle protein was greatest after milk ingestion.
In , Reidy et al. However, when the entire four-hour measurement period was considered, no difference in MPS rates were found. A follow-up publication from the same clinical trial also reported that ingestion of the protein blend resulted in a positive and prolonged amino acid balance when compared to ingestion of whey protein alone, while post-exercise rates of myofibrillar protein synthesis were similar between the two conditions [ ].
Reidy et al. No differences were found between whey and the whey and soy blend. Some valid criteria exist to compare protein sources and provide an objective method of how to include them in a diet. As previously mentioned, common means of assessing protein quality include Biological Value, Protein Efficiency Ratio, PDCAAS and IAAO.
The derivation of each technique is different with all having distinct advantages and disadvantages. For nearly all populations, ideal methods should be linked to the capacity of the protein to positively affect protein balance in the short term, and facilitate increases and decreases in lean and fat-mass, respectively, over the long term.
To this point, dairy, egg, meat, and plant-based proteins have been discussed. As mentioned previously, initial research by Boirie and Dangin has highlighted the impact of protein digestion rate on net protein balance with the two milk proteins: whey and casein [ , , ].
Subsequent follow-up work has used this premise as a reference point for the digestion rates of other protein sources. Using the criteria of leucine content, Norton and Wilson et al.
Wheat and soy did not stimulate MPS above fasted levels, whereas egg and whey proteins significantly increased MPS rates, with MPS for whey protein being greater than egg protein.
MPS responses were closely related to changes in plasma leucine and phosphorylation of 4E—BP1 and S6 K protein signaling molecules. More importantly, following 2- and weeks of ingestion, it was demonstrated that the leucine content of the meals increased muscle mass and was inversely correlated with body fat.
Tang et al. These findings lead us to conclude that athletes should seek protein sources that are both fast-digesting and high in leucine content to maximally stimulate rates of MPS at rest and following training. Moreover, in consideration of the various additional attributes that high-quality protein sources deliver, it may be advantageous to consume a combination of higher quality protein sources dairy, egg, and meat sources.
Multiple protein sources are available for an athlete to consider, and each has their own advantages and disadvantages. Protein sources are commonly evaluated based upon the content of amino acids, particularly the EAAs, they provide. Blends of protein sources might afford a favorable combination of key nutrients such as leucine, EAAs, bioactive peptides, and antioxidants, but more research is needed to determine their ideal composition.
Nutrient density is defined as the amount of a particular nutrient carbohydrate, protein, fat, etc. per unit of energy in a given food.
In many situations, the commercial preparation method of foods can affect the actual nutrient density of the resulting food. When producing milk protein supplements, special preparations must be made to separate the protein sources from the lactose and fat calories in milk. For example, the addition of acid to milk causes the casein to coagulate or collect at the bottom, while the whey is left on the top [ ].
These proteins are then filtered to increase their purity. Filtration methods differ, and there are both benefits and disadvantages to each. Ion exchange exposes a given protein source, such as whey, to hydrochloric acid and sodium hydroxide, thereby producing an electric charge on the proteins that can be used to separate them from lactose and fat [ ].
The advantage of this method is that it is relatively cheap and produces the highest protein concentration [ ]. The disadvantage is that ion exchange filtration typically denatures some of the valuable immune-boosting, anti-carcinogenic peptides found in whey [ ]. Cross-flow microfiltration, and ultra-micro filtration are based on the premise that the molecular weight of whey protein is greater than lactose, and use 1 and 0.
As a result, whey protein is trapped in the membranes but the lactose and other components pass through. The advantage is that these processes do not denature valuable proteins and peptides found in whey, so the protein itself is deemed to be of higher quality [ ]. The main disadvantage is that this filtration process is typically costlier than the ion exchange method.
When consumed whole, proteins are digested through a series of steps beginning with homogenization by chewing, followed by partial digestion by pepsin in the stomach [ ].
Following this, a combination of peptides, proteins, and negligible amounts of single amino acids are released into the small intestine and from there are either partially hydrolyzed into oligopeptides, 2—8 amino acids in length or are fully hydrolyzed into individual amino acids [ ].
Absorption of individual amino acids and various small peptides di, tri, and tetra into the blood occurs inside the small intestine through separate transport mechanisms [ ]. Oftentimes, products contain proteins that have been pre-exposed to specific digestive enzymes causing hydrolysis of the proteins into di, tri, and tetrapeptides.
A plethora of studies have investigated the effects of the degree of protein fractionation or degree of hydrolysis on the absorption of amino acids and the subsequent hormonal response [ , , , , , ]. Further, the rate of absorption may lead to a more favorable anabolic hormonal environment [ , , ].
Calbet et al. Each of the nitrogen containing solutions contained 15 g of glucose and 30 g of protein. Results indicated that peptide hydrolysates produced a faster increase in venous plasma amino acids compared to milk proteins.
Further, the peptide hydrolysates produced peak plasma insulin levels that were two- and four-times greater than that evoked by the milk and glucose solutions, respectively, with a correlation of 0.
In a more appropriate comparison, Morifuji et al. However, Calbet et al. The hydrolyzed casein, however, did result in a greater amino acid response than the nonhydrolyzed casein. Finally, both hydrolyzed groups resulted in greater gastric secretions, as well as greater plasma increases, in glucose-dependent insulinotropic polypeptides [ ].
Buckley and colleagues [ ] found that a ~ 30 g dose of a hydrolyzed whey protein isolate resulted in a more rapid recovery of muscle force-generating capacity following eccentric exercise, compared with a flavored water placebo or a non-hydrolyzed form of the same whey protein isolate.
In agreement with these findings, Cooke et al. Three and seven days after completing the damaging exercise bout, maximal strength levels were higher in the hydrolyzed whey protein group compared to carbohydrate supplementation.
Additionally, blood concentrations of muscle damage markers tended to be lower when four ~g doses of a hydrolyzed whey protein isolate were ingested for two weeks following the damaging bout.
Beyond influencing strength recovery after damaging exercise, other benefits of hydrolyzed proteins have been suggested. For example, Morifuji et al. Furthermore, Lockwood et al. Results indicated that strength and lean body mass LBM increased equally in all groups.
However, fat mass decreased only in the hydrolyzed whey protein group. While more work needs to be completed to fully determine the potential impact of hydrolyzed proteins on strength and body composition changes, this initial study suggests that hydrolyzed whey may be efficacious for decreasing body fat.
Finally, Saunders et al. The authors reported that co-ingestion of a carbohydrate and protein hydrolysate improved time-trial performance late in the exercise protocol and significantly reduced soreness and markers of muscle damage.
Two excellent reviews on the topic of hydrolyzed proteins and their impact on performance and recovery have been published by Van Loon et al. The prevalence of digestive enzymes in sports nutrition products has increased during recent years with many products now containing a combination of proteases and lipases, with the addition of carbohydrates in plant proteins.
Proteases can hydrolyze proteins into various peptide configurations and potentially single amino acids. It appears that digestive enzyme capabilities and production decrease with age [ ], thus increasing the difficulty with which the body can break down and digest large meals.
Digestive enzymes could potentially work to promote optimal digestion by allowing up-regulation of various metabolic enzymes that may be needed to allow for efficient bodily operation.
Further, digestive enzymes have been shown to minimize quality differences between varying protein sources [ ]. Individuals looking to increase plasma peak amino acid concentrations may benefit from hydrolyzed protein sources or protein supplemented with digestive enzymes.
However, more work is needed before definitive conclusions can be drawn regarding the efficacy of digestive enzymes. Despite a plethora of studies demonstrating safety, much concern still exists surrounding the clinical implications of consuming increased amounts of protein, particularly on renal and hepatic health.
The majority of these concerns stem from renal failure patients and educational dogma that has not been rewritten as evidence mounts to the contrary. Certainly, it is clear that people in renal failure benefit from protein-restricted diets [ ], but extending this pathophysiology to otherwise healthy exercise-trained individuals who are not clinically compromised is inappropriate.
Published reviews on this topic consistently report that an increased intake of protein by competitive athletes and active individuals provides no indication of hepato-renal harm or damage [ , ]. This is supported by a recent commentary [ ] which referenced recent reports from the World Health Organization [ ] where they indicated a lack of evidence linking a high protein diet to renal disease.
Likewise, the panel charged with establishing reference nutrient values for Australia and New Zealand also stated there was no published evidence that elevated intakes of protein exerted any negative impact on kidney function in athletes or in general [ ].
Recently, Antonio and colleagues published a series of original investigations that prescribed extremely high amounts of protein ~3. The first study in had resistance-trained individuals consume an extremely high protein diet 4. A protein consists of amino acids AA linked by peptide bonds.
Dietary protein is hydrolyzed by proteases and peptidases to generate AA, dipeptides, and tripeptides in the lumen of the gastrointestinal tract. These digestion products are utilized by bacteria in the small intestine or absorbed into enterocytes.
AA that are not degraded by the small intestine enter the portal vein for protein synthesis in skeletal muscle and other tissues.
AA are also used for cell-specific production of low-molecular-weight metabolites with enormous physiological importance.
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Search Search. Facebook Twitter Email SMS Print Whatsapp Reddit Pocket Flipboard Pinterest Linkedin. By Amy Gorin, RDN. VITAMIN C AND PLANT-BASED IRON To best absorb non-heme iron, aka plant-based iron, you need to give it a little boost by pairing it with a source of vitamin C.
They are provided in two different formats for Proteni and professional Protekn. These resources Protein intake and nutrient absorption produced Organic Dr. Rachel Scherr abslrption her research staff. Produced by Kristen James, BS, Anna M. Jones, PhD, and Rachel E. Scherr, PhD. Protein is a nutrient found in animal and plant foods that provides the body with amino acid building blocks used for many biological roles.
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