The Influence of Training on New Army Recruits’ Energy and Macronutrient Intakes and Performance: A Systematic Literature Review

Abstract

Background: New army recruits undertake initial training to develop their skillset and physical and mental preparedness for military service. Recruits experience a range of stressors both physical and psychological, often at extremes, and in combination. These stressors place recruits at risk of suboptimal energy and macronutrient intakes, which may negatively influence their performance. Objective: The objectives of this systematic literature review are to examine, against the Military Recommended Dietary Intakes (MRDIs), the energy, carbohydrate, protein, and fat intakes of army recruits and trainees undertaking initial training internationally, and identify any associated influence on their performance. Design: A systematic literature review was conducted in accordance with the preferred reporting items for systematic reviews and meta-analyses guidelines. Information sources were searched from their inception until May 2019. Main outcome measures: Outcome data included dietary intakes of energy, carbohydrate, protein, and fat before, during, and/or after army initial training, as well as measures of physical fitness and performance. A custom tool was used to assess the quality of included studies. Results: The results of 14 studies were synthesized. Six were conducted in the United States and four in each of Australia and Israel. Average energy intake represented 69% to 120% of the MRDIs before training commencement, 69% to 106% of the MRDIs in the early weeks of training and 56% to 77% of the MRDIs in the later weeks of training. Average carbohydrate and protein intakes represented 49% to 121% and 64% to 143% of the MRDIs, respectively, across the various time points. Three studies measured physical fitness and/or performance outcomes, with one showing a significant improvement in push-up performance when extra protein was provided. Conclusions: The novel findings of this systematic literature review are that army recruits, internationally, are likely to be underconsuming energy for extended periods of their initial training, with greater deficits in carbohydrate intake compared with other macronutrients. Only a handful of studies investigated the subsequent influents on performance, with no definitive conclusions drawn in most instances. Further research is needed to understand the influence of suboptimal dietary intake on military relevant performance indicators to help better inform key stakeholders when devising nutrition guidance and strategies for army recruits in the future.