Stopping a weight loss diet over the weekends increases fat loss and prevents muscle breakdown
If weight-training people follow a weight-loss diet, they will lose more fat and less muscle if they stop dieting on the weekends and consume just enough calories on those two days to maintain their weight. This is the conclusion of a human study published in the Journal of Functional Morphology and Kinesiology by American sports scientist Bill Campbell of the University of South Florida.
Campbell divided 27 young men and women, who had been training with weights for some time and consumed a relatively large amount of protein, into 2 groups. Both groups went on a weight-loss diet for 7 weeks that provided a quarter less energy per day than the subjects needed to maintain their body weight.

The subjects in the control group dieted every day of the study [continuous].
The subjects in the other group halted the diet on the weekends, and consumed as much energy on Saturday and Sunday as their body burned [refeed]. The 'extra' energy that the subjects consumed on these days came entirely from carbohydrates.

On weekdays, the subjects cut their calorie intake a bit further than the subjects in the control group. On those days, their diet provided 35 percent less energy than it needed to maintain weight.
On a weekly basis, there were no statistically significant differences between the diets of the two groups. [Table]
The subjects in the continous group lost an average of 2.3 kg body fat, the subjects in the refeed group 2.8 kg body weight.

At the same time, the subjects in the refeed group seemed to retain more lean body mass [read: their muscle mass] a little better than the subjects in the continuous group. The refeeders lost 0.4 kg of lean body mass, the subjects in the other group 0.7 kg.More information about the anthropomorphic effects of the two weight loss diets can be found here.
Campbell suspects that discontinuing the weight-loss diet on the weekends helped maintain muscle protein metabolism and synthesis.
"This is the first investigation, to our knowledge, to demonstrate a preservation of fat-free mass and resting metabolic rate in response to a 2-day carbohydrate refeed during an energy restricted diet in lean, resistance trained males and females", write the researchers.

"The attenuation of these adverse responses to caloric restriction may have been dependent on the restoration of true energy balance (or the interruption of continued energy restriction) in the carbohydrate refeed group."
"Our findings suggest that, in lean individuals, the inclusion of resistance training, high protein intakes, a slow rate of weight loss, and periodic carbohydrate refeeding may prevent some of the adverse responses to prolonged energy restriction."
"Future work in this area should determine the effects of single intermittent refeed days (i.e., every third day) as opposed to two consecutive days."
J Funct Morphol Kinesiol. 2020 Mar 8;5(1):19.