Jun 18, 2022
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Is it better to get a diet over with as quickly as possible, dropping as much fat as possible to enable you to get back to muscle building or is a more gradual approach preferred so that there is less risk of lean body mass? Is the loss of lean mass when dieting related to the severity or the length of the diet? These are the kinds of questions we have to ask ourselves when it comes to dieting to determine what the optimal approach is.

The Study​

A recent study conducted by a Norwegian group (1) investigated the effects of dieting approaches, comparing a slow reduction (SR) weight loss of 0.7% of bodyweight/wk to a fast reduction (FR) 1.4% of bodyweight/wk to help answer which is better for preserving lean body mass and performance. The study group measured changes in body composition, strength and power performance across both groups. The study used elite athletes eliminating the possibility that untrained subjects might present a confound in the way they respond.

Skeletal Muscle

24 athletes were randomly assigned to either the SR or FR groups and followed calorie restricted diets for the duration of the study based on the weekly weight loss goals for each group. 4 weight training sessions were performed per week following their usual training routines.

The SR groups spent an average of 8.5 weeks dieting while the FR group got to their target bodyweights in an average of 5.3 weeks. Bodyweight, body composition (DEXA), 1RM tests, 40m sprint time, and counter-movement jumps were tested before and after the diets ended. On average energy intake was reduced in the SR group by 19% while the FR group reduced calories by an average of 30%.


Fat Loss Study

Bodyweight decreased in both SR and FR by 5.6% ± 0.8% and 5.5% ± 0.7% (0.7% of BW/wk on average versus 1.0% of BW/wk). Fat mass reduced by 31% ± 3% in the SR group and 21 ± 4% in the FR group. Lean body mass increased in the SR by 2.1% on average while it decreased slightly by 0.2% in FR.


The Norwegians concluded that if athletes wish to increase LBM and 1RM strength while dieting they should aim for a weekly BW loss of 0.7%.

Our Comments​

This study examined something which previously has not received much research. Within the sport of bodybuilding we have seen a rise in the adoption of rapid fat loss diets aimed at stripping off fat quickly. Examples of this such as the protein sparing modified fast (PSMF) are proclaimed by advocates as avoiding muscle loss compared to normal diets due to the speed with which the diets end, not allowing you to lose significant muscle mass.

This study provides evidence to suggest that these arguments in favour of rapid fat loss diet protocols are not founded on evidence. Having said this, there are some issues with the study which perhaps limits its application.

First, the weight loss was not standardised across the different groups, with differing timeframes for dieting even for some in the same study group. It is possible for instance, if you took two groups and made one diet for 8 weeks (SR) and one diet for 6 weeks (FR) but then follow up for two further weeks of bulking that the results may be different, with the FR group regaining much of the strength and muscle mass they lost. Indeed, this point is one which rapid fat loss diet advocates typically say is a strength of their diet by allowing time spent in a catabolic phase (dieting) to be reduced and more time spent on muscle building.

A second confound with this study is that the athletes were provided a new strength training program and they were due to enter into competition shortly after the conclusion of the study. The introduction of a novel strength program makes it hard to measure the effects of the program in isolation from the diet. A better approach would have been to ensure all participants kept a consistent training regimen both leading into and during the diet as that way the diet’s effects on the body could be measured much more accurately. Some would go further and argue that training volumes for the fast dieting group would ideally be reduced compared to the SR group to more closely resemble the real world training approaches used by rapid dieting proponents to help preserve muscle mass.

Finally, the fact these athletes were from a mish mash of sports and that strength training was not a core activity in any of these sports raises the issue once again that experienced, elite weight trainers would respond differently to how the athletes in this study did. The fact that the SR group got an extra three weeks of strength training time could be a bigger reason for their gain in LBM (which only occurred in the female members in the trial) as opposed to their lower caloric deficits.

It is hard to say unequivocally that the use of a slow reduction diet is superior to a fast reduction diet based purely on this research but, at the very least, it provides some support to those who popularise the slow dieting approach.