Is There an Optimal Time for Warfighters to Supplement with Protein?

Abstract

Although nutritional requirements for warfighters will inevitably vary in accordance with job role and active-inactive duty cycling, somewhat generic recommendations do still apply. In considering aspects of “optimal” nutrient timing, it is important to outline singular and combinatorial relationships between protein intake and physical activity (e.g., exercise) in the context of the following: 1) skeletal muscle protein turnover, 2) functional recovery, and 3) adaptation to exercise. The essential amino acid (EAA) components of dietary protein are key macronutrients regulating muscle proteostasis, because they provide substrate to replenish muscle proteins lost during fasted periods. This occurs through a substantial, albeit short-lived (∼2 h) EAA-induced stimulation of muscle protein synthesis (MPS) and via an insulin-mediated suppression of muscle protein breakdown (MPB) (via carbohydrate- and/or EAA-mediated insulin secretory effects). At rest, intake of protein (optimal range between 20 and 40 g of high-quality protein, equating to ∼10–20 g EAAs) every ∼4–5 h is advocated due to the refractoriness of MPS in response to continuous supply. Bouts of exercise also stimulate muscle protein turnover (increasing both MPS and MPB), but in the absence of protein intake net muscle protein balance remains negative such that exercise alone is catabolic. Intake of dietary protein redresses this balance through enhancing both the amplitude and duration of exercise-induced increases in MPS while concomitantly limiting MPB. These postexercise periods of positive net protein balance permit muscle adaptation and functional recovery. Finally, in relation to exercise, protein dosing (at a minimum of ∼20 g) both in close proximity to exercise and thereafter every 4–5 h during waking hours (including before bedtime) is likely optimal for adaptation/functional recovery.