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Energy, protein, and substrate metabolism in simulated microgravity
K J Acheson1, J Décombaz, C Piguet-Welsch
1Nestec Limited, Nestlé Research Centre, Lausanne, Switzerland.
The American Journal of Physiology
|August 1, 1995
Summary
Simulated microgravity via head-down tilt (HDT) increases energy expenditure and resting metabolic rate in healthy men. These changes may be due to fluid shifts, impacting metabolic responses to glucose.
Area of Science:
- Human Physiology
- Metabolic Studies
- Space Medicine
Background:
- Understanding metabolic and energetic changes during simulated microgravity is crucial for astronaut health.
- The head-down tilt (HDT) model mimics fluid shifts experienced in microgravity.
Purpose of the Study:
- To investigate whole-body protein turnover and energy expenditure during simulated microgravity.
- To assess metabolic responses to an oral glucose tolerance test under HDT conditions.
Main Methods:
- Six healthy young men underwent a 6-degree head-down tilt (HDT) for 42-47 hours.
- Whole-body protein turnover and energy expenditure were measured before and during HDT.
- An oral glucose tolerance test was administered to assess metabolic responses.
Main Results:
- HDT significantly increased basal insulin concentrations and resting metabolic rate (8%).
- Lipid oxidation increased significantly (33%) during HDT.
- No significant changes in glycemia or free fatty acids were observed post-glucose load, though the thermic effect of glucose showed a non-significant increase.
Conclusions:
- Simulated microgravity (HDT) elevates energy requirements through increased basal metabolic rate and thermic response to food.
- Observed metabolic changes may be attributed to cephalic fluid shifts, similar to actual microgravity.
- Protein turnover remained largely unchanged, with minor variations depending on measurement method.