Calorie restriction

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Calorie restriction (CR) means eating fewer calories while still getting all the nutrients you need. People study CR to see if it helps with weight control, aging, and diseases that come with getting older. For many overweight people, CR combined with exercise is recommended to lose weight and improve health. In diabetes and prediabetes, CR may help when paired with activity, with typical goals of about 5-15% weight loss for diabetes and 7-10% for prediabetes to slow or prevent progression.

Pregnant people should only use mild calorie restriction to limit weight gain, not to lose weight.

What the science says about health and aging
- CR can improve health when it leads to weight loss, but many people may regain weight over time.
- Dropping calories too much or not getting enough nutrients can cause malnutrition and serious problems. A famous study during World War II showed severe restriction led to weakness, anemia, swelling, and mental distress.
- Low-calorie plans must still provide essential vitamins and minerals; otherwise people may experience cold intolerance, menstrual changes, or fertility issues.
- Reducing calories by about 20-30% while ensuring nutrient needs are met has shown some promise for aging-related diseases and can lead to significant weight loss. But there is no conclusive evidence that CR extends human lifespan, and results vary.
- People who are very lean or have little body fat may be harmed by too much restriction.

Intermittent fasting and other patterns
- Intermittent fasting—periods with little or no food, such as an 8–12 hour daily eating window—is being studied. It may help heart health and aging, but long-term safety and benefits are not yet clear.
- Some research combines intermittent fasting with a Mediterranean-style diet; more evidence is needed to confirm long-term effects.

What happens in animal and human studies
- In monkeys, results have varied. Some studies showed longer life with restriction, others did not. Factors like age, sex, body weight, and diet quality influence outcomes.
- In older animals, restricting calories with good nutrition often shows more health benefits than in younger ones.
- Researchers think fasting might activate energy-sensing pathways in the body, such as sirtuins, which could influence aging, but the exact effects in humans are not fully understood.

Bottom line
- Calorie restriction can help with weight loss and some health measures, but it must be balanced with good nutrition. It is not a guaranteed way to extend life, and long-term effects in people are still being studied.
- If you’re considering CR, seek medical advice—especially if you are pregnant, very lean, have health conditions, or are at risk for nutrient deficiencies. Focus on gradual, sustainable weight loss with a nutrient-rich diet.