Observations in energy and macronutrient intake during prolonged bed-rest in a head-down tilt position

Objective: to report observations in energy and macronutrient intakes, and body weight duringprolonged bed-rest in a head down tilt (HDT) position. Design: open study, each subject was his own control, and was studied during 14 days of baseline, 42 days of −6° HDT bed-rest, and 12 days of recovery. Subjects: eight healthy young man were recruited, one dropped out. Methods: energy and macronutrientcontent of the diet were calculated from weighed amounts of food consumed and French food composition tables. Results: body weight declined during HDT (74.0±3.2 to 71.8±3.2 kg, P< 0.001) andincreased during recovery (72.7±3.2 kg, P< 0.001). Energy intake decreased during HDT (by 17% after 4–5 weeks) and increased during recovery but remained lower than during baseline (P< 0.001). During HDT fat intake, expressed by a percentage of energy, decreased (P< 0.01) while carbohydrate increased (P = 0.04); protein intake did not change (P = 0.08). The reverse trends were observed during recovery. Conclusions: the present study reports a spontaneous reduction in energy and relative fat intake duringprolonged HDT bed rest. We believe that these findings have implications for the clinical setting.