Evidence suggests that calorie restriction is not effective at causing long term body composition improvements because weight lost initially is nearly always regained. According to research, only 20% of people who undergo weight loss programmes are successful and most individuals who lose weight regain ≈30% within 1 year and ≈95% within 5 years. The main problem with weight loss programmes is that they do not differentiate between body fat and lean mass, and therefore lost weight can be accounted for by decreased bone density and losses of muscle tissue, both of with are detrimental to health. Loss of lean mass is particularly problematic in older individuals, with skeletal muscle loss being associated with an increased risk of all cause mortality. In fact, evidence suggests that lean mass is lost during energy restriction along with body fat, but that subsequent weight regain is made up predominately of just fat.
For example, researchers1 followed up a randomised controlled trial in weight loss involving 78 postmenopausal women in order to assess body composition changes from baseline for up to 12 months following the study. Weight loss was achieved via caloric restriction of roughly 400kcal/d for 5 months, alone, with moderate aerobic exercise or with intense exercise. Whole body fat and lean mass were measured by dual-energy X-ray absorptiometry. The mean weight loss for the women in the study was 11.55kg (12.9%) but there was no difference in weight loss between the groups, suggesting that forced exercise is ineffective at causing weight loss. Fat mass lost was 8.19kg (20.7%) and lean mass lost was 3.65kg (7.0%). Weight regain in the follow up period did not differ between groups. Lost bodyweight regained within 6 months was 4.77kg and within 12 months was 8.42kg (11 and 9% lower than baseline levels).
In this study, there was a great deal of variability between the subjects. For example, 11 of the women weighed more at the 12 month follow up than at baseline, whereas 16 women continued losing weight. Over the course of the follow up, lean mass showed no significant changes between groups, and was still lower than baseline at 12 months. The data showed that as time from the intervention proceeds, in those women who regained ≥2kg weight, the fat mass accretion rate was much higher than the lean mass accretion rate. For these women the weight lost during intervention was 67% fat and 33% lean tissue. But of the weight regained, 79% was fat and 21% was lean tissue. On average 26% of the fat was regained in the follow up period, but only 6% of the lean mass. Therefore the lean-mass to fat mass ration had decreased significantly in the subjects.
This research is not alone in its findings that calorie restriction results in weight regain and a lowering of the lean mass to fat mass in the study participants. Interestingly, data suggests that female participants are more successful at maintaining weight loss than male counterparts, which is why the data from this study is more encouraging than some other published research. The problems associated with the loss of muscle tissue are known to compound the difficulty of subsequent efforts at weight loss because reduced levels of skeletal muscle tissue decrease resting energy expenditure due to the high metabolic activity of muscle tissue. These results highlight further the failure of energy restriction or exercise to cause meaningful long-term improvements in body composition in healthy subjects. Higher intakes of protein and improvements to diet quality, without calorie restriction, may offer a better long term solution to reversing unwanted weight gain.
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