Higher Protein during an Energy Deficit

In this issue of the journal, Pikosky and colleagues (5) present a study in which an exercise-induced energy deficit of 1000 kcal·d−1 was accompanied by consumption of diets differing in macronutrient composition. Specifically, protein was manipulated to be consumed at either 1.0 g·kg−1·d−1 (DEF), which is about 25% greater than the current protein RDA (1) or at 1.75 g·kg−1·d−1 (DEF-HP), which is about 2.2 times the RDA. The increased dietary protein came at the expense of dietary fat, so carbohydrate formed 55% of energy intake in all groups. In a control group, subjects were kept in energy balance (BAL) despite induction of a 1000 kcal·d−1 energy deficit through exercise. One of the most impressive aspects of this study was the tight control that the investigators maintained over the dietary composition and daily energy expenditure. This allowed for some very important trends to be seen even with only 12 d of energy deficit. Measurements of nitrogen balance showed that the BAL group maintained nitrogen balance throughout the study, as did the DEF-HP group. By contrast, the DEF group subjects were in negative nitrogen balance at both 5 and 12 d, indicating that insufficient dietary protein was being consumed to balance losses during the exercise-induced energy deficit. This is an interesting finding because it resurrects an age-old argument over whether exercise (particularly with dietary energy insufficiency) increases, does not change, or even reduces requirements for dietary protein. One can actually find support for all three positions; for recent reviews, see Phillips (3) and Phillips et al. (4). Clearly, while the subjects were in energy deficit, the nitrogen balance results show that extra dietary protein was of benefit in terms of preserving protein mass. How, then, did these findings translate to changes in body composition? Naturally, the BAL group lost only a small amount of lean mass, versus mean declines in fat-bone-free mass of 1.6 ± 0.4 kg in the DEF group and 1.3 ± 0.3 kg in the DEF-HP group. Interestingly, the loss of fat was about 0.4 kg greater in the DEF-HP group, a difference that failed to reach statistical significance but that was attributable, almost certainly, to a type 2 statistical error. Nonetheless, the data are still worthy of further consideration because the changes in body composition occurred in only 12 d. In that period, the seven males in the DEF-HP group, consuming more than twice the RDA for protein, lost 0.3 kg less lean mass and 0.4 kg more fat when placed in a 1000 kcal·d−1 exercise-induced energy deficit. An interesting question is what relative role the exercise and higher protein had in the changes in body composition; others have shown that diet-induced energy deficits in combination with exercise and higher protein shift changes in body composition toward fat and away from lean mass loss (2). It would be interesting to see what might have happened had Pikosky et al. (5) included even a small amount of a potent anabolic stimulus such as resistance exercise, which would likely have provided an additional push to preserve lean mass to an even greater extent. It is unfortunate that Pikosky et al. (5) chose to study their subjects in the fasted state to make their isotopic measures of protein turnover, because it is in the fed state that most changes are likely to occur. Inclusion of these data would have provided some very important mechanistic information regarding the nature of the observed changes in nitrogen balance and body composition. One would predict that if such measures were made that the DEF-HP group would have shown a greater net retention of ingested protein. These data have implications for the design of weight loss programs that are targeted toward loss of stored energy as fat mass and retention of metabolically active muscle mass. Such a pattern of change in body composition obviously represents the most desirable change in the situation of energy deficit, whether induced by dietary or exercise means. Further work in this area should yield some interesting data; however, the study by Pikosky et al. (5) provides some very provocative and intriguing data from which to begin pondering further studies. Stuart M. Phillips Department of Kinesiology Exercise Metabolism Research Group McMaster University Hamilton, Ontario Canada

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