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Abstract

The aim of the present thesis was to examine the effect of normobaric hypoxic
confinement on selected metabolic responses. This was investigated in two separate
studies:
Study I investigated the effect of normobaric hypoxia, as frequently used by athletes
for altitude training, on metabolism. The metabolic responses were assessed in eleven
normal weight aerobically well-trained healthy males after a 10-day hypoxic confinement.
Study II tested the hypothesis that altitude exposure initiates body weight loss in
overweight individuals. Therefore, we evaluated the effects of 10-day normobaric
hypoxic confinement on metabolism in eight overweight males.
Subjects were confined to a normobaric hypoxic environment (HYPOXIA; simulated
altitude ranging from 2800 m to 3400 m) for 10 days, and the responses in the hypoxic
confinement trial compared to those observed in a normoxic confinement trial
(NORMOXIA) of similar duration. The studies were conducted in a facility situated at an
altitude of 940 m and were designed as randomized cross-over studies. The wash-out
period between trials was 3 weeks. During each 10-day period, participants were
restricted from any strenuous physical activity to eliminate the confounding factor of
exercise, and were under continuous nutritional control. Before, and at the end of each
(NORMOXIA and HYPOXIA) confinement, participants completed a meal tolerance test
(MTT) to investigate the postprandial metabolic responses. Resting energy expenditure
(REE), metabolic factors (circulating glucose, GLP-1, insulin, catecholamines, ghrelin,
peptide-YY (PYY), leptin), gastro-intestinal blood flow and appetite sensations were
measured in the fasted and postprandial (2 hrs) states.
Study I: In normal weight individuals (73.0±7.7 kg; 23.7±4.0 yrs, BMI 22.2±2.4 kg·m-
2) body weight was significantly reduced by both confinements (NORMOXIA: -0.7±0.2
kg; HYPOXIA: -0.9±0.2 kg). There was an increase in body fat mass in the NORMOXIA
(0.23±0.45 kg) trial, but no change in fat mass in the HYPOXIA (0.08±0.08 kg) trial.
Hypoxic confinement increased REE and minute ventilation (!") during rest. Decreased
energy intake was attributable to an increased fasting level of leptin in normal weight
aerobically trained individuals. A trend for increased values of blood glucose and insulin
as a response to a test meal were observed after HYPOXIA.
Study II: In overweight individuals (125.0±17.7 kg; 30.5±11.1 yrs, BMI 37.6±6.2
kg·m-2) body weight loss was observed in the HYPOXIA trial in overweight individuals.
After the continuous 10-day hypoxic confinement, REE increased significantly.
Furthermore, concomitant with a tendency for decreased energy intake, there was a
significant increase in PYY at the end of the HYPOXIC trial.
The present studies demonstrate that 10-day normobaric HYPOXIC confinement
increased REE of both normal weight aerobically trained, and overweight individuals.
Although there were no significant differences in subjective satiety scores after
HYPOXIA, we speculate that increased leptin (Study I) and the trend for increased PYY
values (Study II) could be partly responsible for the observed decrease in energy intake
during HYPOXIA. With the exception of the increased postprandial blood glucose
response, 10-day hypoxic confinement did not affect any of the measured blood
parameters and gut blood flow. To conclude, 10-day normobaric hypoxia per se has an
effect on body weight in normal weight and overweight individuals. This is most likely
due to increased REE and increased work of the respiratory muscles associated with the
elevated ventilation during HYPOXIA.