Do female competitors lose more muscle during contest prep?

Short answer

Not in contest-prep studies. In 27 female competitors who dieted for 4 months, body fat was cut in half while lean mass did not drop. Studies comparing men and women found men lost more, or there was no difference. The bigger change for women was irregular periods.

Do female competitors lose more muscle during contest prep?
'Women have less muscle, so they lose more when dieting' — true?
Women have less muscle and lower testosterone than men, so the story goes that dieting for a contest costs them more muscle. We checked studies that measured the bodies of women preparing for physique contests.
27 female competitors who dieted for 4 months
Body weight fell 12%, body fat by half
27 women preparing for a contest lost 11.9% of their body weight over 4 months, and body fat measured by DXA (an X-ray body composition scan) fell 50.4%. They kept up strength training and ate about 200 g of protein a day (average body weight 64 kg).
So how much muscle did they lose?
Lean mass did not drop
In the same 27 women, lean mass (muscle and everything except fat) measured by DXA went from 47.6 kg to 48.0 kg: no drop. A bioimpedance body composition scale (InBody) showed a 3.0% drop, which came back during recovery. Compared with 23 weight-stable women, the DXA values showed no difference.
Side by side with men?
The men lost more lean mass
A study comparing 10 women and 13 men over 23 weeks of contest prep found both lost fat, but the men lost more lean mass. A review of 15 contest-prep case studies also found women kept or slightly increased lean mass, while men tended to lose it.
A 2026 study of 19 men and women
No sign that women lost more
Over about 20 weeks of contest prep, 19 people (8 men, 11 women) lost 7.1 kg on average, 5.8 kg of it fat. Lean mass fell 1.7 kg, with no difference between men and women. 12 weeks after the contest, lean mass was 1.6 kg higher than at the start.
But women did see a different change
Irregular periods became more common
In the 27 women who dieted for 4 months, estrogen and testosterone fell and irregular periods became more common. Among 12 women followed through the last 7 weeks of prep, only 2 still had regular cycles at the end. In the 27 women, hormones returned during a 3 to 4 month recovery, except testosterone and thyroid hormone.
Bottom line: women did not lose more muscle
The bigger change was periods, not muscle
The 27 women who dieted for 4 months did not lose lean mass, and when men and women were compared, men lost more or there was no difference. The women in these studies ate plenty of protein and kept strength training. During prep, what women competitors need to watch is changes in their cycle more than muscle.