Faster weight loss can sound appealing, especially with alternate-day fasting, which pairs very low-calorie days with days of regular eating. But a new suggests that the quickest results may come with tradeoffs.
About the study
Researchers followed 35 adults with obesity through a 62-day alternate-day fasting program.
During the first 32 days, fasting days became increasingly restrictive, eventually reaching one-quarter of participants’ usual calorie intake.
On nonfasting days, participants could eat freely, though very high-fat meals were discouraged. For the final 30 days, participants ate 500 to 600 calories on fasting days with less supervision.
Researchers measured weight, fat mass, lean mass, blood pressure, and blood markers at the start, day 16, day 32, and day 62. They paid particular attention to uric acid, which is linked to gout and cardiovascular health.
The weight came off, but not all of it was fat
After 62 days, participants lost about 6.8 kilograms, or roughly 7% of their starting weight.
Their waist circumference and visceral fat also decreased. However, during the most restrictive phase, nearly one-quarter of the weight lost came from lean mass, which includes muscle.
Uric acid levels rose almost 9% during that phase. When the diet became less restrictive, some lean mass returned and uric acid levels fell below baseline.
Participants who lost more lean mass also tended to experience larger uric acid increases. This was an association, not proof that muscle loss caused the rise.
Why muscle matters
Weight loss is generally healthier when most of it comes from fat rather than muscle. supports strength, mobility, physical activity, and healthy aging. Losing too much can make it harder to maintain a healthy body composition, even if the scale shows progress.
Uric acid also deserves attention. Higher levels can raise gout risk and are associated with cardiovascular problems, although no participants developed gout during the trial.
The rise during the strictest phase and decline after easing the diet suggest that the intensity of calorie restriction may affect the body’s response.
How to protect muscle
If you use fasting or another calorie-restricted approach, prioritize and Both can help preserve lean mass during weight loss.
The study’s main lesson is about pace: the most aggressive phase produced the fastest weight loss, but also the largest changes in lean mass and uric acid.
A smaller calorie deficit may be slower, but it could better support muscle, nutrition, and long-term sustainability.