Does a carb refeed during a diet protect your muscle?

Short answer

No muscle protection showed up. The 2-day refeed study that claimed it lost the difference on reanalysis, and even 1-week breaks made no difference to muscle. The bigger look after a refeed was a one-day change; what changed was hunger and appetite.

Does a carb refeed during a diet protect your muscle?
'More carbs → body recovers → muscle kept' — does this formula hold?
A common claim is that a 'refeed', a day or two of high carbs during a diet, stops muscle loss. We checked studies that actually measured muscle, covering refeeds and longer 'diet breaks'.
One study said refeeds saved muscle
2 refeed days a week for 7 weeks
27 people trained while cutting calories by about 25% for 7 weeks. Those who raised carbs 2 days each week lost 0.4 kg of lean mass (muscle and everything except fat), while those who dieted straight through lost 1.3 kg. The authors concluded refeeds protected muscle.
A reanalysis told a different story
The muscle difference disappeared
When other researchers reanalyzed the same data, the change in lean mass showed no difference between the groups. The only gap left was in lean mass with body water removed. Of the 54 people first tested, only 27 finished.
What about longer breaks than a refeed?
1-week breaks made no difference to muscle
61 people compared 3 weeks of dieting followed by 1 week at maintenance calories against 12 weeks of straight dieting. At the end, lean mass was 56.7 kg in both groups, and strength showed no difference. A study of 38 people also found no difference in body composition.
Do you train better on a refeed day?
Performance stayed the same
After 4 weeks of dieting, 11 people did the same hard leg workout on a diet day and on a carb refeed day. The refeed did not change performance. Muscle soreness dropped only in the 5 people who had cut calories hard.
Why muscles look bigger after a refeed
Muscle got thicker in a single day
15 people who cut carbs for 3 days and then ate lots of carbs for 24 hours saw arm muscle thickness and body measurements rise, while 9 who skipped the carb load stayed the same. A one-day change is not new muscle growth. 7 of the 15 had diarrhea.
What changed instead was appetite
Less hunger and fewer urges to binge
In the 61-person study, the group with 1-week breaks felt less hungry. In the 38-person study, a score for losing control and overeating rose from 4.91 to 6.17 with straight dieting, but fell from 6.80 to 6.05 with breaks.
Bottom line: a refeed is not a muscle shield
Think of it as a break for appetite
The refeed study that claimed muscle protection lost its difference on reanalysis, and even 1-week breaks made no difference to muscle. The bigger look after a refeed was a one-day change. A refeed is best seen as a break that helps with hunger and appetite, not a way to keep muscle.