A growing number of people are experimenting with alternate-day fasting (ADF) as a flexible alternative to traditional calorie restriction.
But new research published in Nutrients indicates that the strategy may have drawbacks that merit closer scrutiny.
While participants lost weight rapidly, they also lost lean tissue, a finding that could reshape how ADF is viewed in weight-management circles.
Four weeks of ADF
The research team examined how four weeks of ADF affected young Asian men with overweight or obesity.
Also read: Why cold weather might complicates weight loss goals
Participants alternated between unrestricted eating days and fasting days limited to water, calorie-free drinks, and a single small meal at midday.
Body composition, fasting glucose, blood pressure, and reported physical activity were monitored each week.
A second group followed the same fasting pattern but received an additional 25-gram whey protein supplement on fasting days.
The aim was to test whether a modest protein boost could counteract the muscle loss often associated with dieting.
Also read: Research shows bedtime stability may help lower blood pressure
Muscle decline
According to the study’s findings, the fasting protocol produced significant reductions in both body weight and fat mass.
These rapid changes support previous observations that ADF places the body in a sustained energy deficit.
However, the researchers also documented a decline in fat-free mass, a category largely made up of muscle.
Metabolic indicators such as diastolic blood pressure and fasting glucose showed only temporary shifts during individual weeks, with no lasting improvements by the end of the trial.
Also read: Scientists explain how much water a healthy body can process safely
Physical activity levels dropped mid-study, which may have contributed to the observed muscle loss.
Protein supplement falls short
The added whey protein had little impact. The study authors note that the dose was relatively small and did not bring fasting-day protein intake up to recommended levels.
Without data on protein consumption on non-fasting days, the researchers could not determine whether participants met daily overall requirements.
The findings suggest that although ADF may deliver fast weight-loss results, it may not be appropriate for individuals hoping to maintain muscle mass.
Also read: Researchers identify unexpected age effects in cancer formation
The authors recommend future trials combining higher protein intake with resistance training to determine whether muscle loss can be reduced.
Sources: News-Medical, and Nutrients.
Also read: She drank olive oil for two weeks – here’s what happened