Requirements for protein for the general population are defined by various agencies but generally appear in the range of 0.8–0.9 g protein/kg/day. In Canada and the US the recommended dietary allowance (RDA) defines the RDA as “… the average daily intake level that is sufficient to meet the nutrient requirement of nearly all [98 %] healthy individuals …”. The panel also states that “… no additional dietary protein is suggested for healthy adults undertaking resistance or endurance exercise” [1, 2]. It may be true that the basal ‘requirement’ for protein, even for the most intensely training athlete, is satisfied by the protein RDA. That is, 0.8 g protein/kg/day can satisfy the needs for all amino acid-requiring processes and that most athletes could likely even achieve nitrogen balance when consuming this intake; however, a pertinent question is whether such a state would result due to some adaptive change in an amino acid-requiring process and whether this adaptive change would compromise some goal in an athlete? Nevertheless, this is not a question that is easy to answer as a number of reviews [3, 4] and position stands [5] have concluded higher protein is required for athletes. The problem then of the discrepancy between population estimates of protein requirements [1, 2] and position stands on protein requirements for athletes [3–5] is more than likely that minimal intakes of protein can sustain normal function for the general population, but athletes are trying to optimize their adaptation to training. Thus, protein ‘requirements’ is the wrong term to use when referring to an athlete, and a more precise term to use is that of defining an optimal protein intake for an athletic population versus a protein intake to achieve nitrogen balance [1, 2]. This sentiment may be particularly true during an energy deficit when the choice of which macronutrients to consume may be even more critical, at least from an athlete’s perspective.

A thermodynamic reality of weight loss in humans (i.e. a net oxidation of stored substrates) is that total ingested energy needs to be less than total energy expenditure over some defined period of time. The result is a net loss of body weight that is usually comprised, from a tissue standpoint, of stored lipid and lean tissues in a ratio of about 3:1 [6]. A more rapid weight loss can shift this ratio toward greater lean tissue loss [7] even in athletes [8]. From an athlete’s standpoint it may be more important to favor weight loss that emphasizes fat loss and muscle preservation, which may be more conducive to preservation or increases in performance. In addition, in a number of sports it is generally recognized that a high strength, power, or endurance to body weight ratio is desirable. We have referred previously to weight loss that has a high fat:lean ratio as higher quality weight loss [9]. In fact, in certain circumstances it is desirable for athletes to increase their lean mass while losing weight [10].

The aim of this article is to provide a brief review of the evidence examining why protein might be considered the macronutrient around which to base a hypocaloric weight loss diet owing to its role in satiety, thermogenesis, maintenance of lean mass, and utility in supporting adaptation to training.