Effects of 21 days of bed rest, with or without artificial gravity, on nutritional status of humans

Spaceflight and bed rest models of microgravity have profound effects on physiological systems, including the cardiovascular, musculoskeletal, and immune systems. These effects can be exacerbated by suboptimal nutrient status, and therefore it is critical to monitor nutritional status when evaluating countermeasures to mitigate negative effects of spaceflight. As part of a larger study to investigate the usefulness of artificial gravity as a countermeasure for musculoskeletal and cardiovascular deficits during bed rest, we tested the hypothesis that artificial gravity would have an effect on some aspects of nutritional status. Dietary intake was recorded daily before, during, and after 21 days of bed rest with artificial gravity (n = 8) or bed rest alone (n = 7). We examined body composition, hematology, general blood chemistry, markers of oxidative damage, and blood levels of selected vitamins and minerals before, during, and after the bed rest period. Several indicators of vitamin status changed in response to diet changes: serum alpha- and gamma-tocopherol and urinary 4-pyridoxic acid decreased (P < 0.001) and plasma beta-carotene increased (P < 0.001) in both groups during bed rest compared with before bed rest. A decrease in hematocrit (P < 0.001) after bed rest was accompanied by a decrease in transferrin (P < 0.001), but transferrin receptors were not changed. These data provide evidence that artificial gravity itself does not negatively affect nutritional status during bed rest. Likewise, artificial gravity has no protective effect on nutritional status during bed rest.

Nutritional status assessment in semiclosed environments: ground-based and space flight studies in humans

Adequate nutrition is critical during long-term spaceflight, as is the ability to easily monitor dietary intake. A comprehensive nutritional status assessment profile was designed for use before, during and after flight. It included assessment of both dietary intake and biochemical markers of nutritional status. A spaceflight food-frequency questionnaire (FFQ) was developed to evaluate intake of key nutrients during spaceflight. The nutritional status assessment protocol was evaluated during two ground-based closed-chamber studies (60 and 91 d; n = 4/study), and was implemented for two astronauts during 4-mo stays on the Mir space station. Ground-based studies indicated that the FFQ, administered daily or weekly, adequately estimated intake of key nutrients. Chamber subjects maintained prechamber energy intake and body weight. Astronauts tended to eat 40--50% of WHO-predicted energy requirements, and lost >10% of preflight body mass. Serum ferritin levels were lower after the chamber stays, despite adequate iron intake. Red blood cell folate concentrations were increased after the chamber studies. Vitamin D stores were decreased by > 40% on chamber egress and after spaceflight. Mir crew members had decreased levels of most nutritional indices, but these are difficult to interpret given the insufficient energy intake and loss of body mass. Spaceflight food systems can provide adequate intake of macronutrients, although, as expected, micronutrient intake is a concern for any closed or semiclosed food system. These data demonstrate the utility and importance of nutritional status assessment during spaceflight and of the FFQ during extended-duration spaceflight.

Physiological and hormonal responses of lambs repeatedly implanted with zeranol and provided two levels of feed intake

Forty crossbred wethers (average weight 30 kg) were implanted with zeranol (12 mg) at 30-d intervals and fed at two levels of intake in a 2 x 2 factorial arrangement of treatments to determine performance, carcass and bone characteristics, blood metabolites, and hormones. Restricted lambs were fed to gain one-half the BW gained by lambs with ad libitum feed access. Lambs with ad libitum and restricted access to feed were slaughtered after 98 and 154 d, respectively. Zeranol increased ADG (P = .047; 20%), gain to feed (P = .023; 17%), metacarpal length (P = .004; 6%) and weight (P = .013; 13%), and tended to increase carcass crude protein gain (P = .106; 63%) while reducing kidney pelvic fat (P = .001; 33%) and dressing percentage (P = .038; 3%). Restricted feed intake increased the percentage of carcass ash and metacarpal length and weight by 27% (P = .048), 5% (P = .006), and 10% (P = .045), respectively, while reducing quality grade scores (P = .022; 5%), gain to feed (P = .001; 49%), longissimus muscle area (P = .001; 28%), the percentage of kidney pelvic fat (P = .033; 13%), and daily fat gain (P = .001; 54%). Zeranol increased pituitary weight (P = .001; 166%), plasma glucose (P = .036; 13%), mean serum growth hormone (GH; P = .011; 52%), baseline GH (P = .048; 34%), GH pulse amplitude (P = .003; 59%), and IGF-I (P = .001; 53%) concentrations. The results indicate that continuous administration of zeranol from 60 d of age to slaughter increases GH release, which directs nutrient utilization such that a carcass with more desirable lean and fat deposition patterns is obtained when nutrient availability is adequate.