Research

Energy balance

Three weeks of 40% caloric restriction in normal-weight young men suppresses leucine flux and oxidation during exercise, yet preserves whole-body aerobic performance despite significant lean mass loss.

If you are a fit young male restricting calories by 40% for three weeks, expect to lose about 2kg of lean mass. However, your ability to perform aerobic exercise (like cycling endurance) will likely remain unchanged because your body adapts by reducing protein breakdown during activity. Do not assume performance will drop just because you are in a deficit.

GoodQualifiesHIGH confidence
In conclusion, 3 wk of caloric restriction reduced leucine flux and Rox during exercise in normal-weight young men. However, despite negative nitrogen balance and loss of lean mass, whole body exercise performance was well maintained in response to CR.
Anne L. Friedlander et al. · American Journal of Physiology-Endocrinology and Metabolism · 2005

Why this rating

Randomized controlled trial with stable isotope tracing in a controlled environment, though small sample size (n=9).

Source

Three weeks of caloric restriction alters protein metabolism in normal-weight, young men

Anne L. Friedlander et al. · American Journal of Physiology-Endocrinology and Metabolism · 2005

DOI 10.1152/ajpendo.00001.2005

crossover · n=9Cited 57×
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DOI resolved against Crossref · corpus check 2026-06-10

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