Energy expenditure and balance during spaceflight on the space shuttle

Abstract

The objectives of this study were as follows: 1) to measure human energy expenditure (EE) during spaceflight on a shuttle mission by using the doubly labeled water (DLW) method; 2) to determine whether the astronauts were in negative energy balance during spaceflight; 3) to use the comparison of change in body fat as measured by the intake DLW EE,18O dilution, and dual energy X-ray absorptiometry (DEXA) to validate the DLW method for spaceflight; and 4) to compare EE during spaceflight against that found with bed rest. Two experiments were conducted: a flight experiment ( n = 4) on the 16-day 1996 life and microgravity sciences shuttle mission and a 6° head-down tilt bed rest study with controlled dietary intake ( n = 8). The bed rest study was designed to simulate the flight experiment and included exercise. Two EE determinations were done before flight (bed rest), during flight (bed rest), and after flight (recovery). Energy intake and N balance were monitored for the entire period. Results were that body weight, water, fat, and energy balance were unchanged with bed rest. For the flight experiment, decreases in weight (2.6 ± 0.4 kg, P < 0.05) and N retention (−2.37 ± 0.45 g N/day, P < 0.05) were found. Dietary intake for the four astronauts was reduced in flight (3,025 ± 180 vs. 1,943 ± 179 kcal/day, P < 0.05). EE in flight was 3,320 ± 155 kcal/day, resulting in a negative energy balance of 1,355 ± 80 kcal/day (−15.7 ± 1.0 kcal ⋅ kg−1 ⋅ day−1, P < 0.05). This corresponded to a loss of 2.1 ± 0.4 kg body fat, which was within experimental error of the fat loss determined by18O dilution (−1.4 ± 0.5 kg) and DEXA (−2.4 ± 0.4 kg). All three methods showed no change in body fat with bed rest. In conclusion, 1) the DLW method for measuring EE during spaceflight is valid, 2) the astronauts were in severe negative energy balance and oxidized body fat, and 3) in-flight energy (E) requirements can be predicted from the equation: E = 1.40 × resting metabolic rate + exercise.

Calorie restriction accelerates the catabolism of lean body mass during 2 wk of bed rest

“…Anorexia in space can lead to food intakes Ȃ20 -30% lower than preflight and postflight intakes (8,11,22), which can result in an average weight loss of Ȃ0.5 kg for each week spent in space (8). Potential causes for this weight loss may include alterations in circadian rhythms, gastrointestinal function, and neuroendocrine mediators and cytokines and space motion sickness, exposure to radiation energy, and busy work schedules (11).…”

Large-scale mRNA analysis of female skeletal muscles during 60 days of bed rest with and without exercise or dietary protein supplementation as countermeasures

“…Skylab space missions were the first to include a countermeasure program involving astronaut exercises ranging from 30 to 90 min/day with a clear emphasis on aerobic metabolism (25). Both space and ground experiments have already demonstrated that maximal resistance exercise is effective in preserving muscle structure and function (3,79,80) and that nutritional aid is key in the maintenance of the muscle mass, well-being and performance of the astronauts (70,72). However, there is a scarcity of information concerning the impact of different countermeasures on the molecular processes and signaling pathways involved in skeletal muscle disuse atrophy.…”

The deleterious effects of bed rest on human skeletal muscle fibers are exacerbated by hypercortisolemia and ameliorated by dietary supplementation

“…Ferrando et al (4) observed a 50% drop in protein synthesis with no change in protein breakdown in the vastus lateralis (VL) of subjects following a 14-day BR. In many space crew members and patients confined to BR, the extent of muscle protein breakdown was exacerbated by an inadequate energy intake, which resulted in a negative caloric balance (14,16,17). In patients, the incidence of undernutrition during hospitalization has been estimated to be as high as 50% (1).…”