Back in the 90s, I devised a fat loss program for women that involved using a meal replacement drink of my own design and a then-novel portion control system for the other, non-protein drink meals that were also part of the plan. We had TV commercials and a full-page ad in USA Today, the works.
What made the diet especially appealing to women, though, was the inclusion of a weekend "cheat day" or two. This was a fairly novel concept back then. In fact, I'm not sure if any other diets of the day prescribed them.
Anyhow, my rationale was that the day(s) off would prevent muscle wasting and that it might "reset" the dieter's metabolism, but I secretly feared I was full of shit because there wasn't any pertinent research back then to back it up.
What I was sure of, though, was that women loved getting the weekends off from the drudgery of their diets so they wouldn't have to watch their friends and family members gorge on carb-heavy meals and be tempted to Lizzie Borden them with a heavy lasagna knife or pizza spatula.
It turns out, though, that I might have been right (even a blind squirrel, etc., etc.) about the validity of cheat days, though, because a recent study – apparently the first of its kind – showed that stopping a weight loss diet over the weekends and doing a carb "refeed" not only prevents muscle wasting, but also increases fat loss.
Sports scientist Bill Campbell of the University of South Florida recruited 58 weight-trained men and women and divvied them up into two groups. Both groups went on a 7-week diet where they averaged 25% fewer weekly calories than needed to maintain body weight. Both groups also participated in equivalent weight-lifting programs that were matched for total volume of work.
All participants were fed 1.8 grams of protein per kg of body mass and the remaining calories were split evenly between fat and carbohydrate.
One of the two groups, however, stopped their diet on weekends to "refeed." This didn't involve pigging out, though. Instead, they just upped their caloric intake to match what they'd normally eat before the diet started, i.e., their weight-maintenance calories. But here's the fun part: All of the extra energy came from carbs.
There was a small but important difference in the protocols of the two groups, though. The continuous dieting group ate 25% fewer calories than required for maintenance every day for 7 continuous weeks.
The refeed group, though, consumed 35% fewer calories than needed for maintenance of body weight for 5 days and then ingested 100% of their maintenance calories during the weekend.
Even so, both groups averaged exactly 25% fewer calories than needed for maintenance every week.
Unfortunately, a lot of the initial group of 58 wussed out and only 27 completed the study. Of the remaining 27, those in the refeed group lost an average of 2.8 kg of body fat while the people in the continuous dieting group lost an average of 2.3 kg body fat. The subjects in the refeed group also lost less muscle mass than the continuous dieting group, 0.4 kg to 0.7 kg.
Campbell, in the discussion section of his paper, wrote:
"...a consecutive two-day carbohydrate refeed preserves fat-free mass during an energy restricted diet as compared to continuous energy restriction in a population (lifters and bodybuilders) that prioritizes the maintenance of muscle mass when dieting. A secondary finding was that resting metabolic rate was better maintained, albeit slightly, with the two-day carbohydrate refeed."
Campbell wasn't sure why the results panned out the way they did, but he theorizes that maybe not being in a caloric deficit for two days per week could have "blunted the catabolic environment for skeletal muscle" that you often see when diets go on for extended periods without any breaks.
Alternately, he guessed that the weekend refeeds might have increased glycogen stores in the refeed group, which might have led to less fatigue and allowed the subjects to train harder, thus leading to greater fat loss and less muscle loss.
In what's pretty rare these days, Campbell et al., rather than just throw the results out into the ether for us to make our own assumptions, actually dared to suggest some practical applications for their findings:
"If a lean, resistance-trained individual seeks to reduce caloric intake for the purpose of fat loss, this should be undertaken with relatively high protein intakes, a slow rate of weight loss, and periodic carbohydrate refeeding."
- Campbell BI et al. Intermittent Energy Restriction Attenuates the Loss of Fat Free Mass in Resistance Trained Individuals. A Randomized Controlled Diet. J Funct Morphol Kinesiol. 2020 Mar 8;5(1):19. PubMed.