Calorie Restrictive Diet

Rodent experiments in the 1930s

A 2017 review by Ingram and de Cabo credits McCay and colleagues in 1935 with describing the prolongevity effects of restricting the food available to rats and so retarding their growth. The review says this work became one of the most widely used tools of biogerontologists over the following eight decades. It also describes a 1941 follow-up in older rats, whose data were later reanalyzed and read as showing longer lifespan when restriction began at mature ages.

A 2011 review by Speakman and Mitchell states that restricting intake has been practiced as a method of increasing the length and quality of life for over 500 years, and that experimental work in animals has accumulated over the last 100 years. Only the abstract of that review was open for this record, so the 500-year statement is the authors' own and was not traced to primary sources here.

Primate studies at Wisconsin and the National Institute on Aging

Two long-running rhesus monkey studies began in the late 1980s, one at the Wisconsin National Primate Research Center and one at the National Institute on Aging (NIA). The Wisconsin group reported in 2009 that, at the time point reported, 50% of control animals had survived against 80% of animals on moderate restriction, and that restriction delayed several age-associated diseases. The NIA group reported in 2012 that its restriction regimen had not improved survival, although it documented health effects.

A 2014 Wisconsin paper argued that the NIA control monkeys were effectively undergoing restriction because their body weights were lower than those of Wisconsin controls. A 2017 joint comparison by both groups described differences in study design that could contribute to the different survival results, including onset age, diet and feeding of controls. The two studies are therefore not simple repeats of one another.

Human studies and the Calorie Restriction Society

Most and colleagues describe members of the Calorie Restriction Society as people who follow a self-imposed, severe form of restriction with what they call optimal nutrition, abbreviated CRON. A 2004 study compared 18 such individuals, who had restricted for an average of about 6 years, with 18 age-matched people eating typical American diets. The restricted group was leaner and had lower values for several cardiovascular risk markers.

The CALERIE program, a US multicenter series of trials, tested sustained reduction of energy intake in healthy adults. Dorling and colleagues describe its second phase as the largest study to date of sustained restriction in healthy humans without obesity, with outcomes centered on aging biomarkers and not on survival.

Two senses of the term

The sources reviewed use calorie restriction, caloric restriction and dietary energy restriction for a reduction in energy intake. In aging research the review literature defines it as a nutritional intervention of reduced energy intake but with adequate nutrition. Cava and Fontana write that excessive dietary restriction and overnutrition are different forms of malnutrition, which marks the line between the research sense and simple under-eating.

In clinical weight-management guidance the same idea appears as an energy deficit, meaning total energy intake kept below energy expenditure. NICE guideline NG246 separates ordinary dietary approaches from low-energy and very-low-energy diets, which are defined, time-limited programs run within specialist services. This page treats the aging-research sense and the weight-management sense separately because their populations, aims and time frames differ.

Related Machipedia pages

CRON stands for calorie restriction with optimal nutrition, a label used by self-practicing groups in the sources. The Dietary Approaches page covers the wider family of eating patterns to which this entry belongs and is not repeated here. Intermittent Fasting, Mediterranean Diet, Mindful Eating Therapy, Dietetics and Nutritional Therapy have their own pages. NICE lists intermittent fasting in adults as a topic for research and makes no recommendation on it.

Long-term restriction in research

In CALERIE phase 2, 218 healthy adults aged 21 to 50 started the study and were assigned in a 2 to 1 ratio to a prescribed reduction in energy intake or to eating as usual for two years. This describes trial design and is not guidance. Participants in the restriction group achieved an average reduction of 11.9%, well below the prescribed level, and lost an average of 7.5 kg.

Short-term restriction in weight management

NICE guideline NG246 (published January 2025, last updated January 2026) says dietary approaches for adults should keep total energy intake below energy expenditure, by lowering specific macronutrient content or by other methods of limiting intake. It asks for a flexible, individualized approach that keeps nutritional balance, with support from an appropriately trained professional such as a registered dietitian or registered nutritionist.

The 2022 Academy of Nutrition and Dietetics guideline for dietitians says interventions should include a nutritionally adequate diet with adjusted energy intake, behavioral strategies such as self-monitoring, and appropriate physical activity. It states that many dietary patterns can be adapted for weight management and does not prescribe one diet.

Low-energy and very-low-energy diets

NICE says low-energy diets may be considered only within a multicomponent strategy in a specialist service, for people with obesity or with overweight and type 2 diabetes. Very-low-energy diets may be considered only for people with obesity and a clinically assessed need to lose weight rapidly. Both must be nutritionally complete, last no more than 12 weeks and include clinical supervision, and neither is a long-term strategy.

Dietitians and professional bodies

The British Dietetic Association says dietitians complete an approved degree route, with supervised practice, and must be on the register of the Health and Care Professions Council, which it describes as protecting the title. It says other nutrition titles such as nutritionist are not protected in the same way. Training and registration of dietitians in the United States were not checked for this record.

Aging and longevity research

Researchers studying long-term restriction hold that it may slow aspects of aging. Waziry and colleagues frame their analysis around the geroscience hypothesis, the idea that slowing the molecular changes of aging could delay or prevent several chronic diseases. These are research hypotheses. None of the sources reviewed reports that restriction extends human lifespan.

Weight and cardiometabolic goals

In clinical weight management, energy restriction is used to lower body weight. The Academy guideline says weight loss of about 3 to 5% may bring cardiometabolic benefits and that a larger loss may suit people with obesity or related conditions. NICE adds that people should be encouraged to improve their diet even without weight loss, because other health benefits such as an improved lipid profile can follow.

Animal studies

In rhesus monkeys, the Wisconsin study reported better survival with restriction and the NIA study did not, although both documented health effects. The joint 2017 comparison concluded that health benefits were conserved in monkeys and pointed to differences in onset and diet. For rodents, Ingram and de Cabo describe results that depend on age at onset, strain, sex, diet composition and schedule, with some studies finding no benefit. Rodent findings do not establish effects in humans.

CALERIE trial results in healthy adults

In the exploratory analysis of CALERIE phase 2, restriction relative to control produced lower LDL cholesterol and blood pressure, lower C-reactive protein and improved insulin sensitivity and metabolic syndrome score at two years. Mean weight fell 7.5 kg, of which 71% was fat mass. Participants were healthy, lean or slightly overweight adults aged 21 to 50, and the outcomes were exploratory.

A post hoc analysis found that restriction slowed the pace of aging measured by the DunedinPACE DNA methylation algorithm but produced no significant change in biological age estimated by other clocks, including PhenoAge and GrimAge. The authors describe the effect sizes as small and say a conclusive test needs long-term trials with chronic disease and mortality endpoints. A separate analysis found improved mood and reduced tension at 24 months.

Human lifespan and mortality

Cava and Fontana write that whether restriction extends human lifespan is not yet known, and that randomized long-term survival studies in humans are unlikely to be performed because of problems with long-term compliance. Most and colleagues state that data on longevity and mortality were not yet available for Calorie Restriction Society members. The CALERIE trials measured biomarkers and did not report lifespan.

Weight-management guidance and trials

The Academy guideline drew on 67 randomized and 3 non-randomized trials. It reports that weight regain is common without extended care, that follow-up beyond two years has not been studied, and that evidence on quality of life and mental health is limited. NICE notes that weight regain may happen and advises against restrictive diets that are nutritionally unbalanced, saying they are ineffective in the long term and can be harmful.

Selected populations and short follow-up

CALERIE enrolled healthy adults and screened out people with eating disorders, depression and several medical conditions, so its results do not describe the general population. The Calorie Restriction Society comparison involved 18 self-selected people against 18 controls and cannot separate the diet from other differences between groups. Both bodies of evidence examine markers, not disease outcomes or survival.

Different settings, different evidence

Animal results, human trials of long-term restriction and guidelines on short-term weight-management diets answer different questions in different populations. Findings from one setting should not be carried to another: rodent and primate survival data do not show a human lifespan effect, and guideline evidence in people with overweight or obesity does not show that restriction is useful for healthy people seeking longevity.

Bone and lean mass

In CALERIE phase 2, bone mineral density fell at the lumbar spine, total hip and femoral neck relative to control at 24 months, and fat-free mass fell by 2.2 kg against 0.2 kg. The authors called bone loss at fracture-prone sites a potential limitation of prolonged restriction. Three participants were withdrawn for safety reasons, two for low hematocrit and one for bone loss, and the authors advised close monitoring for bone loss and anemia.

Menstrual function, cold and libido

In CALERIE reproductive-system disorders were reported by 24.5% of the restriction group and 14.7% of controls, a difference that was not statistically significant. No amenorrhea was reported, though most women used oral contraceptives. Most and colleagues list impaired menstrual cycles and cold sensitivity among side effects that deter severe restriction, without citing a source for them, and Speakman and Mitchell report that long-term practitioners describe hunger, feeling cold and reduced libido.

Mood and eating-disorder risk

In the screened CALERIE sample mood did not worsen, and no participants were removed by the eating-disorder screening. Some eating-behavior scores shifted, including avoidance of forbidden foods. Most and colleagues cite the 1940s Minnesota study of severe restriction, where emotional distress developed. NICE notes that people can be affected by an eating disorder at any weight and says to offer assessment before low-energy diets, and the NHS advises seeking medical advice first with a current or past eating disorder.

Who it is not suited to

Cava and Fontana write that severe restriction could be detrimental for children, older adults and pregnant women. The Academy guideline says energy-reduced approaches may not suit people with active eating disorders, and weight loss may be inappropriate in pregnancy, during chemotherapy and for some older adults. NICE advises avoiding overly restrictive diets for children and young people. A conventional clinician should be consulted and care for any medical condition should not be delayed or replaced.