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1 Department of Surgery, School of Osteopathic Medicine, University of Medicine and Dentistry of New Jersey, Stratford, New Jersey 08084; and 2 Institute for Biomedical Problems, Moscow 123007, Russia
Human spaceflight
is associated with a loss of body protein. Bed rest studies suggest
that the reduction in the whole body protein synthesis (PS) rate should
be ~15%. The objectives of this experiment were to test two
hypotheses on astronauts and cosmonauts during long-duration (>3 mo)
flights on MIR: that 1) the whole
body PS rate will be reduced and 2)
dietary intake and the PS rate should be increased postflight because
protein accretion is occurring. The
15N glycine method was used for
measuring whole body PS rate before, during, and after long-duration
spaceflight on the Russian space station MIR. Dietary intake was
measured together with the protein kinetics. Results show that subjects
lost weight during flight (4.64 ± 1.0 kg,
P < 0.05). Energy intake was
decreased inflight (2,854 ± 268 vs. 2,145 ± 190 kcal/day,
n = 6, P < 0.05), as was the PS rate (226 ± 24 vs. 97 ± 11 g protein/day, n = 6, P < 0.01). The reduction in PS
correlated with the reduction in energy intake (r2 = 0.86, P < 0.01, n = 6). Postflight energy intake and
PS returned to, but were not increased over, the preflight levels. We
conclude that the reduction in PS found was greater than predicted from ground-based bed rest experiments because of the shortfall in dietary
intake. The expected postflight anabolic state with increases in
dietary intake and PS did not occur during the first 2 wk after landing.
energy
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