Effectiveness of nutritional countermeasures in microgravity and its ground-based analogues to ameliorate musculoskeletal and cardiopulmonary deconditioning-A Systematic Review


Abstract

A systematic review was performed to evaluate the effectiveness of nutrition as a standalone countermeasure to ameliorate the physiological adaptations of the musculoskeletal and cardiopulmonary systems associated with prolonged exposure to microgravity. A search strategy was developed to find all astronaut or human space flight bed rest simulation studies that compared individual nutritional countermeasures with non-intervention control groups. This systematic review followed the guidelines of the Cochrane Handbook for Systematic Reviews and tools created by the Aerospace Medicine Systematic Review Group for data extraction, quality assessment of studies and effect size. To ensure adequate reporting this systematic review followed the guidelines of the Preferred Reporting Items for Systematic Review and Meta-Analyses. A structured search was performed to screen for relevant articles. The initial search yielded 4031 studies of which 10 studies were eligible for final inclusion. Overall, the effect of nutritional countermeasure interventions on the investigated outcomes revealed that only one outcome was in favor of the intervention group, whereas six outcomes were in favor of the control group, and 43 outcomes showed no meaningful effect of nutritional countermeasure interventions at all. The main findings of this study were: (1) the heterogeneity of reported outcomes across studies, (2) the inconsistency of the methodology of the included studies (3) an absence of meaningful effects of standalone nutritional countermeasure interventions on musculoskeletal and cardiovascular outcomes, with a tendency towards detrimental effects on specific muscle outcomes associated with power in the lower extremities. This systematic review highlights the limited amount of studies investigating the effect of nutrition as a standalone countermeasure on operationally relevant outcome parameters. Therefore, based on the data available from the included studies in this systematic review, it cannot be expected that nutrition alone will be effective in maintaining musculoskeletal and cardiopulmonary integrity during space flight and bed rest.

Conflict of interest statement

The funder (KBR GmbH) provided support in the form of salaries for authors [DAG, TW] but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. This does not alter our adherence to PLOS ONE policies on sharing data and materials.

Figures

Fig 1
Fig 1. PRISMA flow diagram.
Summary of literature search and screening process. This figure was adapted and modified from Fiebig et al. [35]. CM = countermeasure.
Fig 2
Fig 2. Effect size plot of operationally relevant muscle outcomes.
Effect size plot of operationally relevant muscle outcomes categorized into ‘muscle volume’, ‘muscle power’ and ‘muscle force’. Effect sizes were calculated by the mean differences between the control and intervention group of pre and post bed rest values with Hedges’ G and bias corrected for sample size with a confidence interval of 95%. All calculated effect sizes were defined as small (0.2), medium (0.5), large (0.8) or very large (1.3). The right direction on the x-axis indicates a positive effect of the intervention and the left direction on the x-axis indicates a negative effect of the intervention. CSA = cross sectional area; LPD = leucine protein diet; max = maximum; MHC = myosin heavy chain; Po = peak force.
Fig 3
Fig 3. Effect size plot of operationally relevant bone outcomes.
Effect sizes were calculated by the mean differences between the control and intervention group of pre and post bed rest values with Hedges’ G and bias corrected for sample size with a confidence interval of 95%. All calculated effect sizes were defined as small (0.2), medium (0.5), large (0.8) or very large (1.3) The right direction on the x-axis indicates a positive effect of the intervention and the left direction on the x-axis indicates a negative effect of the intervention. BMC = bone mineral content; BMD = bone mineral density; LPD = leucine protein diet.
Fig 4
Fig 4. Effect size plot of operationally relevant cardiopulmonary outcomes.
Effect sizes were calculated by the mean differences between the control and intervention group of pre and post bed rest values with Hedges’ G and bias corrected for sample size with a confidence interval of 95%. All calculated effect sizes were defined as small (0.2), medium (0.5), large (0.8) or very large (1.3). The right direction on the x-axis indicates a positive effect of the intervention and the left direction on the x-axis indicates a negative effect of the intervention. HR = heart rate; LPD = leucine protein diet; VO2max = volume oxygen maximum.
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