Moreover, in the calorie-restricted individuals, no adverse effects and some favorable ones were found on quality of life, mood, sexual function , and sleep. The calorie-restriction intervention did cause slight declines in bone density, lean body mass, and aerobic capacity the ability of the body to use oxygen during exercise.

However, these declines were generally no more than expected based on participants' weight loss. Other short-term studies have found that combining physical activity with calorie restriction protects against losses of bone, muscle mass, and aerobic capacity.

Some CALERIE participants also experienced brief episodes of anemia diminished number of circulating red blood cells that carry oxygen through the body. Overall, these findings indicate that while the degree of calorie restriction in CALERIE is safe for normal-weight or moderately obese people, clinical monitoring is recommended.

Most research to date has focused on the weight-loss aspect of fasting, primarily in obese people, and only a few small clinical trials have been conducted. More work is needed to determine which, if any, types of fasting diets have long-term benefits.

Observational studies have been conducted in people who practice fasting in one form or another. In an observational study, the investigator does not determine the treatment to offer and does not randomize subjects into a control group or experimental group.

Instead, the investigator records data from real-life situations. For example, one observational study compared people who routinely fasted as part of a religious practice or for another reason to those who did not fast.

It found that those who routinely fasted were less likely to have clogged arteries or coronary artery disease.

However, the study did not control for other factors that could have affected the results, such as the kind of diet, quality of food consumed, or use of nutritional supplements. After decades of research, scientists still don't know why calorie restriction extends lifespan and delays age-related diseases in laboratory animals.

Do these results come from consuming fewer calories or eating within a certain timeframe? Are the results affected by the diet's mix of nutrients? Several studies have focused on what occurs inside the body when caloric intake is restricted.

In laboratory animals, calorie restriction affects many processes that have been proposed to regulate the rate of aging. These include inflammation, sugar metabolism, maintenance of protein structures, the capacity to provide energy for cellular processes, and modifications to DNA. Another process that is affected by calorie restriction is oxidative stress, which is the production of toxic byproducts of oxygen metabolism that can damage cells and tissues.

Several of these processes were similarly affected by calorie restriction in the human CALERIE trial. However, we do not yet know which factors are responsible for calorie restriction's effects on aging or whether other factors contribute. Research supported by NIA has also focused on the effects of intermittent fasting.

During fasting, the body uses up glucose and glycogen, then turns to energy reserves stored in fat. This stored energy is released in the form of chemicals called ketones.

These chemicals help cells—especially brain cells—keep working at full capacity. Some researchers think that because ketones are a more efficient energy source than glucose, they may protect against aging-related decline in the central nervous system that might cause dementia and other disorders.

Ketones also may inhibit the development of cancer because malignant cells cannot effectively obtain energy from ketones. In addition, studies show that ketones may help protect against inflammatory diseases such as arthritis. Ketones also reduce the level of insulin in the blood, which could protect against type 2 diabetes.

But too many ketones in the blood can have harmful health effects. This is one of the reasons researchers want to understand more about how calorie restriction diets work before recommending them.

Most calorie-restriction and fasting-diet studies have been in younger people, but researchers are beginning to study older adults. A clinical trial conducted by NIA is testing the diet in obese people, age 55 to 70, with insulin resistance. This is a condition in which cells do not respond normally to the hormone insulin.

This can lead to serious diseases such as diabetes. People in the experimental group can eat at will for 5 days, and then for 2 consecutive days are restricted to to calories per day. The experiment is designed to find out how 8 weeks of the diet, compared to a regular diet, affects insulin resistance and the brain chemicals that play a role in Alzheimer's disease.

In the coming years, researchers will continue to explore many unresolved questions. What are the long-term benefits and risks of the various eating patterns?

Which diets are feasible as a long-term practice? What specific biological effects on aging and disease are triggered by a particular eating pattern? If a specific way of eating is recommended, at what age is it best to start, and is it safe to continue as you get older?

There's insufficient evidence to recommend any type of calorie-restriction or fasting diet. A lot more needs to be learned about their effectiveness and safety, especially in older adults. You may be tempted to try one of these eating patterns. It's important to make sure that whatever you try provides you with a safe level of nutrition.

Talk with your healthcare provider about the benefits and risks before making any significant changes to your eating pattern. An official website of the National Institutes of Health. Share: Print page Facebook share Linkedin share X social media share.

Research Highlights Calorie restriction and fasting diets: What do we know? August 14, On this page: What Are the Different Forms of Calorie Restriction and Fasting?

What's the Evidence from Animal Studies? What's the Evidence from Human Studies of Calorie Restriction? What's the Evidence from Human Studies of Fasting? For those who need fewer calories, a 1,calorie diet may be safe and effective for weight loss. A person may need more calories than others if they are male, very active, pregnant or nursing, or have a certain medical condition.

This article explains the safety and effectiveness of a 1,calorie diet for weight loss, including meal ideas and frequently asked questions. The average adult needs 1,—3, calories daily to sustain their body weight. When someone consumes fewer calories than they need, the body begins to shed weight.

It does this first by burning fat and eventually other tissue, including muscle. Most people need significantly more than 1, calories a day. Therefore, individuals who cut their daily intake to 1, calories can expect to lose some weight. This can be beneficial for people with overweight or obesity.

The National Institute on Aging highlights research that suggests that low calorie diets may offer additional health benefits. In animal studies, lower-calorie diets helped animals live longer and reduced the risk of diseases such as cancer.

However, further studies are necessary. Not all research on animals applies to humans. Other factors may also be responsible for improved health, such as the specific foods people eat when following a low calorie diet.

A review suggests that other factors contribute to weight management, such as meal timing and the type of food a person eats. Some research also notes that weight loss is about more than the calories a person consumes and burns. The body may change the rate at which it burns calories depending on how many calories a person eats.

Therefore, an individual on a 1,calorie diet may burn fewer of them. This can slow weight loss. It is possible that some people might not lose any weight or will need to remain on a restricted calorie diet for a significant time before experiencing results.

Weight loss will also vary between people. For some people, an alternative approach, such as getting more exercise or consuming less sugar , might be a more suitable option. It is more difficult to get essential macronutrients , such as proteins and fats , and micronutrients, including vitamins and minerals, on a low calorie diet.

Therefore, it is important to read nutritional labels and talk with a healthcare professional before trying this method of eating. A dietitian can help people create a personalized eating plan.

A 1,calorie diet can potentially be unhealthy for some people. For example, someone who receives all their calories from sweetened cereal, potato chips, or cookies may experience malnourishment.

A major risk of long-term calorie restriction is malnutrition. This can affect the body in the following ways:.

People on a 1,calorie diet need to eat nutrient-dense food to avoid feeling hungry and prevent malnourishment. Lean proteins tend to be very dense in nutrients and low in calories. By contrast, white carbohydrates , such as white bread, contain more calories and fewer nutrients.

The National Heart, Lung, and Blood Institute provides menu plans and other information about which foods to choose when following a 1,calorie diet. Following a 1,calorie diet does not necessarily mean a person has to avoid any specific foods entirely. Allowing an occasional small treat may make it easier to stick to this restrictive diet.

However, very high calorie foods, such as large muffins or slices of cake, can make it difficult to stay under 1, calories for the day while maintaining nutritional needs. Eliminating empty calories from the diet can free up more space for treats.

Some sources of empty calories include:. A calorie deficit is one of the most important factors for weight loss. However, other factors, such as meal timing and the type of food someone eats, will also contribute to weight loss. Weight loss may not happen the same way for every person.

Some people may lose weight faster than others or benefit from different methods. It may also be difficult to consume all necessary nutrients on very low calorie diets.

People can work with a healthcare professional to ensure they are eating a balanced diet while still achieving a safe calorie deficit.

Reducing the number of calories a person consumes can help them lose weight.