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Research

Caloric Restriction

Sustained energy reduction without malnutrition that improves several cardiometabolic markers in non-obese adults but has not been shown to extend human lifespan.

Moderate
Evidence rating
Evidence review

What the evidence says

Caloric restriction means sustained energy intake below usual needs while preserving adequate protein, micronutrients, and clinical safety. It is not synonymous with fasting, crash dieting, or pursuing the lowest possible body weight.[1]

In CALERIE, 218 healthy non-obese adults were assigned to a 25% restriction target or an ad-libitum control for two years. Participants achieved about 12% average restriction and roughly 10% weight loss, with improvements in blood pressure, lipids, insulin sensitivity, and inflammatory or cardiometabolic measures.[1][2]

Trial analyses found no overall deterioration in quality of life and reported improvements in several mood, sleep, and sexual-function measures. A biological-aging analysis found a small slowing signal in one composite algorithm, but surrogate clocks are not evidence of longer life or less disability.[3][4]

Restriction reduced both fat and lean mass and raises practical concerns about bone density, fertility, cold intolerance, food preoccupation, and undernutrition. A meta-analysis found bone-mineral-density loss with calorie restriction, making resistance exercise, protein, nutrients, and individual risk assessment important.[2][5]

Potential benefits

  • Improves several cardiometabolic risk markers over two years in healthy non-obese adults.[1]
  • Can reduce fat mass and body weight while preserving acceptable self-reported quality of life under intensive monitoring.[2][3]

Side effects and cautions

  • Lean-mass and bone-density loss, fatigue, cold sensitivity, hunger, and nutrient inadequacy are plausible or observed tradeoffs.[2][5]
  • It is inappropriate without specialist oversight for eating disorders, pregnancy, frailty, underweight, growth, or many chronic diseases.[3]
How we scored it

Evidence breakdown

The two-year CALERIE randomized trial demonstrates feasible partial restriction and biomarker changes, while longevity, long-term safety, and generalizability remain unresolved.

Clinical relevanceModerate

Human trials measure risk factors, body composition, quality of life, and biological-aging algorithms, not lifespan.

Study qualityHigh

CALERIE was a two-year multicenter randomized controlled trial with detailed phenotyping.

Safety dataModerate

Two-year monitoring exists, but lifelong restriction and vulnerable populations remain poorly characterized.

References

Full source list

  1. Effect of 2 years of calorie restriction on cardiometabolic risk factors in non-obese humans

    The Lancet Diabetes & Endocrinology · 2019

  2. Body-composition changes in the CALERIE-2 study: a 2-year randomized controlled trial of calorie restriction in nonobese humans

    American Journal of Clinical Nutrition · 2017

  3. Effects of calorie restriction on quality of life, mood, sexual function, and sleep in nonobese healthy adults

    JAMA Internal Medicine · 2016

  4. Caloric restriction decreases biological aging in healthy, nonobese adults

    Journals of Gerontology: Biological Sciences · 2018

  5. The effects of weight loss approaches on bone mineral density in adults: a systematic review and meta-analysis of randomized controlled trials

    Osteoporosis International · 2016