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All You Need to Know about Weight Loss, NO Exercise needed - Andrew Huberman - #weightloss #fatlossFat oxidation and weight loss -
For the most part, adipocytes are located just under the skin throughout the body as well as in regions surrounding vital organs for protection called visceral fat.
Most of the fat inside the adipocytes is in the form of a triacylglycerol TAG or triglyceride. TAGs are composed of a backbone glycerol with 3 fatty acid tails. Depending on energy supply and demand, adipocytes can take up and store fat from the blood or release fat back to the blood.
After eating, when energy supply is high, the hormone insulin keeps the fatty acids inside the adipocyte Duncan et al. After a few hours of fasting, or especially during exercise, insulin levels tend to drop while other hormones such as epinephrine otherwise called adrenaline increase.
When epinephrine binds to the adipocyte it causes lipolysis of the TAG stores in the adipocyte Duncan et al. Lipolysis is the separation of the fatty acids from the glycerol backbone. After lipolysis, the fatty acids and glycerol can leave the adipocyte and enter the blood.
Fatty Acids In the Blood The blood is an aqueous water based environment. Because fat is not water-soluble i. The primary protein carrier for fat in the blood is albumin Holloway et. One albumin protein can carry multiple fatty acids through the blood to the muscle cell Horowitz and Klein, In the very small blood vessels capillaries surrounding the muscle, fatty acids can be removed from albumin and taken into the muscle Holloway et al.
Fatty Acids From the Blood into the Muscle In order for fatty acids to get from the blood into the muscle they must cross two barriers. The first is the cell lining that makes up the capillary called the endothelium and the second is the muscle cell membrane known as the sarcolemma.
Fatty acid movement across these barriers was once thought to be extremely rapid and unregulated Holloway et al. More recent research shows that this process is not nearly as rapid as once thought and that it requires special binding proteins present at the endothelium and sarcolemma to take in fatty acids Holloway et al.
The Two Fates of Fat Inside the Muscle Once inside the muscle, a molecule called Coenzyme A CoA is added to the fatty acid Holloway et al. CoA is a transport protein which maintains the inward flow of fatty acids entering into the muscle and prepares the fatty acid for two fates: 1 oxidation a process in which electrons are removed from a molecule to produce energy or, 2 storage within the muscle Holloway et al.
Fat that is stored inside the muscle is called intramyocellular triacylglycerol IMTAG or intramuscular fat. The amount of IMTAG in slow twitch muscles the slow oxidative fibers is two to three times greater than the IMTAG stored in fast twitch muscles fibers Shaw, Clark and Wagenmakers.
This is because it is a metabolically active fatty acid substrate especially used during periods of increased energy expenditure, such as endurance exercise. Fatty Acids Burned for Energy Fatty acids burned for energy oxidized in the muscle can either come directly from the blood or from the IMTAG stores.
In order for fatty acids to be oxidized, they must be transported into the cell's mitochondria. The mitochondrion is an organelle that functions like a cellular power plant.
The mitochondrion processes fatty acids and other fuels to create a readily usable energy currency ATP to meet the energy needs of the muscle cell. Most fatty acids are transported into the mitochondria using a shuttle system called the carnitine shuttle Holloway et al.
The carnitine shuttle works by using two enzymes and carnitine an amino acid-like molecule to bring the fatty acids into the mitochondria. One of these enzymes is called carnitine palmitoyl transferase I CPTI. Once inside the mitochondria, fatty acids are broken down through several enzymatic pathways including beta-oxidation, tricarboxylic acid cycle TCA , and the electron transport chain to produce ATP.
Focus Paragraph: An Overview of Fat Metabolism in the Mitochondrion Fatty acids are transported into the muscle where they are either stored as IMTAG or transported into the mitochondrion, which can be referred to as the fat-burning furnace in a person's body cells as this is the only place TAG are completely broken down.
The electron transporters take the electrons to the electron transport chain for further oxidation, which leads to a liberation of energy that is used to produce adenosine triphosphate ATP. Unused energy becomes heat energy to sustain the body's core temperature.
This ATP synthesizing process depends upon a steady supply of oxygen, which is why this process is aptly nicknamed aerobic metabolism or aerobic respiration. Fatty Aid Oxidation During a Single Bout of Exercise At the start of exercise blood flow increases to adipose tissue and muscle Horowitz and Klein, This allows for increased fatty acid release from adipose tissue and fatty acid delivery to the muscle.
Exercise intensity has a great impact on fat oxidation. This counterintuitive drop in fat utilization during high intensity exercise is caused by several factors. One factor is related to blood flow to adipose tissue and thus reduced fatty acid supply to the muscle.
At high exercise intensity, blood flow is shunted or directed away from adipose tissue so that fatty acids released from adipose tissue become trapped in the adipose capillary beds, and are not carried to the muscle to be used Horowitz and Klein, Another reason for reduced fat usage at high exercise intensities is related to the enzyme CPT1.
CPT1 is important in the carnitine shuttle that moves fatty acids into the mitochondria for oxidation. The activity of CPT1 can be reduced under conditions of high intensity exercise. Two mechanisms are thought to reduce CPT1 activity during intense exercise.
As stated above, with increasing exercise intensity fatty acid oxidation drops while carbohydrate oxidation increases. The increased usage of carbohydrate leads to increased levels of a molecule called malonyl CoA inside the cell Horowitz and Klein, Malonyl CoA can bind to and inhibit the activity of CPT1 Achten and Jeukendrup, Another way intense exercise may reduce CPT1 activity is by changes in cellular pH.
The cellular pH is the measure of the acidity in the cell's cytoplasm fluid in terms of the activity of hydrogen ions. As exercise intensity increases the muscle becomes more acidic. Increased acidity which means the pH is lowering can also inhibit CPT1 Achten and Jeukendrup, The reason for the increased acidity during high intensity exercise is not because of lactic acid formation as once thought.
Instead, acidosis increases because the muscle is using more ATP at the contracting muscle fibers just outside of the mitochondria , and the splitting of ATP releases many hydrogen ions into the cellular fluid sarcoplasm leading to the acidosis in the cell Robergs, Ghiasvand and Parker, Too much emphasis is often placed on percent of fatty acid contribution of Calories burned during a single bout of exercise.
Recovery from a bout of exercise as well as training adaptations to repeated bouts are important to consider when working with clients with fat loss goals. Focus Paragraph.
The Splitting of Adenosine Triphosphate ATP ATP is split by water called hydrolysis with the aid of the ATPase enzyme. During intense exercise there is a high level of hydrolysis of ATP by the muscles fibers.
Each ATP molecule that is split releases a hydrogen ion, which is the cause of acidosis in the cell Robergs, Ghiasvand and Parker, This acidosis can slow the carnitine shuttle that moves fatty acids into the mitochondria for oxidation.
This elevated metabolic rate is termed excess post exercise oxygen consumption EPOC. EPOC appears to be greatest when exercise intensity is high Sedlock, Fissinger and Melby, For example, EPOC is higher after high intensity interval training HIIT compared to exercise for a longer duration at lower intensity Zuhl and Kravitz, EPOC is also notably observed after resistance training Ormsbee et al.
EPOC is particularly elevated for a longer period of time after eccentric exercise due to additional cellular repair and protein synthesis needs of the muscle cells Hackney, Engels, and Gretebeck, Many studies also show that during the period of EPOC, fat oxidation rates are increased Achten and Jeukendrup, , Jamurtas et al.
Comparatively, fatty acid use during high intensity bouts of exercise such as HIIT and resistance training may be lower as compared to moderate intensity endurance training; however, high intensity exercise and weight training may make up for this deficit with the increased fatty acid oxidation through EPOC.
Comparison of Effect of Light Exercise versus Heavy Exercise on EPOC Some key factors that contribute to the elevated post-exercise oxygen consumption during high intensity exercise include the replenishment of creatine phosphate, the metabolism of lactate, temperature recovery, heart rate recovery, ventilation recovery, and hormones recovery Sedlock, Fissinger and Melby, Interestingly, lipolysis breakdown of fats to release fatty acids and fat release from adipocytes is not different between untrained and trained people Horowitz and Klein, This suggests that the improved ability to burn fat in trained people is attributed to differences in the muscle's ability to take up and use fatty acids and not the adipocyte's ability to release fatty acids.
The adaptations that enhance fat usage in trained muscle can be divided into two categories: 1 those that improve fatty acid availability to the muscle and mitochondria and 2 those that improve the ability to oxidize fatty acids.
Fatty acid availability One way exercise can improve fatty acid availability is by increasing fatty acid transport into the muscle and mitochondria.
As mentioned above, specific proteins mediate transport of fatty acids into the muscle and mitochondria. Together these proteins will improve fat transport into the muscle and mitochondria to be used for energy. Exercise may also cause changes in the intramuscular lipid droplet that contains IMTAGs.
The intramuscular lipid droplet is mostly found in close proximity to the mitochondria Shaw, Clark and Wagenmakers, Having IMTAGs close to the mitochondria makes sense for efficient IMTAG usage so that fatty acids released from the lipid droplet do not have to travel far to reach the mitochondria.
Exercise training can further increase IMTAG availability to the mitochondria by causing the lipid droplet to conform more closely to the mitochondria.
This increases surface area for more rapid fatty acid transport from the lipid droplet into the mitochondria Shaw, Clark and Wagenmakers, Exercise training may also increase the total IMTAG stores Shaw, Clark and Wagenmakers, Another training adaptation that may improve fatty acid availability is increased number of small blood vessels within the muscle Horowitz and Klein, Remember, fatty acids can enter the muscle through the very small blood vessels.
Increasing the number of capillaries around the muscle will allow for increased fatty acid delivery into the muscle. Fatty acid breakdown IMTAGs are a readily available substrate for energy during exercise because they are already located in the muscle.
Trained athletes have an increased ability to use IMTAG efficiently during exercise Shaw, Clark and Wagenmakers, Athletes also tend to have larger IMTAG stores than lean sedentary individuals. Overweight and obese individuals, interestingly, also have high levels of IMTAG but are not able to use IMTAGs during exercise like athletic individuals can Shaw, Clark and Wagenmakers, So what causes the reduced ability to use IMTAGs in obese individuals?
A logical guess would be that they have dysfunctional mitochondria that cannot use fatty acid properly. Research has shown however, that the mitochondria from muscles of obese individuals are not dysfunctional Holloway et al.
Instead, the number of mitochondria per unit of muscle mitochondrial density is reduced in an obese population Holloway et al. Reduced mitochondrial density is a more likely explanation for reduced ability to use fat for energy in obese individuals. An important adaptation to exercise training is increased mitochondrial density Horowitz and Klein ; Zuhl and Kravitz, Increasing mitochondrial density would improve the ability to use fat and benefit individuals with fat loss goals.
Endurance exercise training is an effective way to improve the body's fatty acid usage abilities by improving the availability of fatty acids to the muscle and mitochondria and by increasing fatty acid oxidation Horowitz and Klein, HIIT training has also been shown to result in similar fat burning adaptations while requiring fewer workouts and less total time commitment Zuhl and Kravitz, Practical application Rather than trying to maximize fat oxidation in a single bout of exercise, it is recommended that the personal trainer design a workout program aimed at causing muscle adaptations described above to improve fatty acid oxidation ability.
The exercise professional should include interval and endurance training programs as these have been shown to improve mitochondrial density and fat oxidation Zuhl and Kravitz, In addition, regular progressively increasing programs of resistance training are encouraged as this training will enhance EPOC and post-workout fat oxidation.
Also, the personal trainer should encourage the client to engage in low to moderate intensity exercise such as walking and cycling on off hard workout days in order to enhance caloric deficit and support muscle adaptions between training days.
Workout examples High intensity interval training HIT with variable recovery modified from Seiler and Hetlelid, High intensity interval training uses exercise intensity that corresponds to the individual's VO2max. Seiler and Hetlelid exercised subjects at their highest running speeds for 4 minutes with 1, 2 or 4 minutes of recovery and repeated this interval 6 times.
The idea of a systematic variation of the recovery is a very novel approach to interval training and certainly warrants more research. The workout Have the client complete up to 6 sets of 4-minute bouts at a maximal sustained workout effort and vary each recovery period to be 1 min, 2 min or 4 minutes at a light intensity client's self-selected intensity.
Sprint interval training SIT Modified from Burgomaster et al. When training was conducted in the fasted state, the researchers observed a decrease in muscle glycogen use, while the activity of various proteins involved in fat metabolism was increased. However, fat oxidation during exercise was the same in the two groups.
It is possible, though, that there are small but significant changes in fat metabolism after fasted training; but, in this study, changes in fat oxidation might have been masked by the fact that these subjects received carbohydrate during their experimental trials. It must also be noted that training after an overnight fast may reduce your exercise capacity and may therefore only be suitable for low- to moderate- intensity exercise sessions.
The efficacy of such training for weight reduction is also not known. Duration of exercise — It has long been established that oxidation becomes increasingly important as exercise progresses.
During ultra-endurance exercise, fat oxidation can reach peaks of 1 gram per minute, although as noted in Dietary effects fat oxidation may be reduced if carbohydrate is ingested before or during exercise. In terms of weight loss, the duration of exercise may be one of the key factors as it is also the most effective way to increase energy expenditure.
Mode of exercise — The exercise modality also has an effect on fat oxidation. Fat oxidation has been shown to be higher for a given oxygen uptake during walking and running, compared with cycling 7.
The reason for this is not known, but it has been suggested that it is related to the greater power output per muscle fibre in cycling compared to that in running.
Gender differences — Although some studies in the literature have found no gender differences in metabolism, the majority of studies now indicate higher rates of fat oxidation in women. In a study that compared men and women over a wide range of exercise intensities, it was shown that the women had higher rates of fat oxidation over the entire range of intensities, and that their fat oxidation peaked at a slightly higher intensity 8.
The differences, however, are small and may not be of any physiological significance. There are many nutrition supplements on the market that claim to increase fat oxidation.
These supplements include caffeine, carnitine, hydroxycitric acid HCA , chromium, conjugated linoleic acid CLA , guarana, citrus aurantium, Asian ginseng, cayenne pepper, coleus forskholii, glucomannan, green tea, psyllium and pyruvate.
With few exceptions, there is little evidence that these supplements, which are marketed as fat burners, actually increase fat oxidation during exercise see table 1. One of the few exceptions however may be green tea extracts. The mechanisms of this are not well understood but it is likely that the active ingredient in green tea, called epigallocatechin gallate EGCG — a powerful polyphenol with antioxidant properties inhibits the enzyme catechol O-methyltransferase COMT , which is responsible for the breakdown of noradrenaline.
This in turn may result in higher concentrations of noradrenaline and stimulation of lipolysis, making more fatty acids available for oxidation. Environment — Environmental conditions can also influence the type of fuel used. It is known that exercise in a hot environment will increase glycogen use and reduce fat oxidation, and something similar can be observed at high altitude.
Similarly, when it is extremely cold, and especially when shivering, carbohydrate metabolism appears to be stimulated at the expense of fat metabolism.
At present, the only proven way to increase fat oxidation during exercise is to perform regular physical activity. Exercise training will up-regulate the enzymes of the fat oxidation pathways, increase mitochondrial mass, increase blood flow, etc.
Research has shown that as little as four weeks of regular exercise three times per week for minutes can increase fat oxidation rates and cause favourable enzymatic changes However, too little information is available to draw any conclusions about the optimal training programme to achieve these effects.
In one study we investigated maximal rates of fat oxidation in subjects with varying fitness levels. In this study, we had obese and sedentary individuals, as well as professional cyclists 9.
VO2max ranged from Interestingly, although there was a correlation between maximal fat oxidation and maximal oxygen uptake, at an individual level, fitness cannot be used to predict fat oxidation.
What this means is that there are some obese individuals that have similar fat oxidation rates to professional cyclists see figure 2! The large inter-individual variation is related to factors such as diet and gender, but remains in large part unexplained.
Fat burning is often associated with weight loss, decreases in body fat and increases in lean body mass. However, it must be noted that such changes in body weight and body composition can only be achieved with a negative energy balance: you have to eat fewer calories than you expend, independent of the fuels you use!
The optimal exercise type, intensity, and duration for weight loss are still unclear. Current recommendations are mostly focused on increasing energy expenditure and increasing exercise volumes.
Finding the optimal intensity for fat oxidation might aid in losing weight fat loss and in weight maintenance, but evidence for this is currently lacking. It is also important to realise that the amount of fat oxidised during exercise is only small.
Fat oxidation rates are on average 0. So in order to oxidise 1kg of fat mass, more than 33 hours of exercise is required! The duration of exercise, however, plays a crucial role, with an increasing importance of fat oxidation with longer exercise.
Of course, this also has the potential to increase daily energy expenditure. If exercise is the only intervention used, the main goal is usually to increase energy expenditure and reduce body fat. When combined with a diet programme, however, it is mainly used to counteract the decrease in fat oxidation often seen after weight loss Higher fat oxidation rates during exercise are generally reflective of good training status, whereas low fat oxidation rates might be related to obesity and insulin resistance.
The vast majority of nutrition supplements do not have the desired effects. Currently, the only highly effective way to increase fat oxidation is through exercise training, although it is still unclear what the best training regimen is to get the largest improvements.
Finally, it is important to note that there is a very large inter-individual variation in fat oxidation that is only partly explained by the factors mentioned above. This means that although the factors mentioned above can influence fat oxidation, they cannot predict fat oxidation rates in an individual.
Asker Jeukendrup is professor of exercise metabolism at the University of Birmingham. He has published more than research papers and books on exercise metabolism and nutrition and is also consultant to many elite athletes. They use the latest research to improve performance for themselves and their clients - both athletes and sports teams - with help from global specialists in the fields of sports science, sports medicine and sports psychology.
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Fat Burning: using body fat instead of carbohydrates as fuel Base endurance training by Asker Jeukendrup. Fat oxidation during exercise Fats are stored mostly in subcutaneous adipose tissue, but we also have small stores in the muscle itself intramuscular triglycerides. Factors affecting fat oxidation Exercise intensity — One of the most important factors that determines the rate of fat oxidation during exercise is the intensity.
Nutrition supplements There are many nutrition supplements on the market that claim to increase fat oxidation. Exercise training At present, the only proven way to increase fat oxidation during exercise is to perform regular physical activity. Weight loss exercise programmes Fat burning is often associated with weight loss, decreases in body fat and increases in lean body mass.
Summary Higher fat oxidation rates during exercise are generally reflective of good training status, whereas low fat oxidation rates might be related to obesity and insulin resistance.
References J Appl Physiol , Int J Sports Med , Int J Sports Med 26 Suppl 1: S, Am J Clin Nutr , J Sports Sci , J Appl Physiol , Metabolism , J Appl Physiol , Nutrition , J Appl Physiol , Int J Obes Relat Metab Disord 17 Suppl 3: S; discussion S, Read More If the pounds come off deceptively easily, beware!
It's not fat that you're losing.
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