The effect of moderate versus severe simulated altitude on appetite, gut hormones, energy intake and substrate oxidation in men

Acute exposure to high altitude (>3500m) is associated with marked changes in appetite regulation and substrate oxidation but the effects of lower altitudes are unclear. This study examined appetite, gut hormone, energy intake and substrate oxidation responses to breakfast ingestion and exercise at simulated moderate and severe altitudes compared with sea-level. Twelve healthy males (mean±SD; age 30±9years, body mass index 24.4±2.7kg.m-2) completed in a randomised crossover order three, 305 minute experimental trials at a simulated altitude of 0m, 2150m (~15.8% O2) and 4300m (~11.7% O2) in a normobaric chamber. Participants entered the chamber at 8am following a 12h fast. A standardised breakfast was consumed inside the chamber at 1h. One hour after breakfast, participants performed a 60 minute treadmill walk at 50% of relative V̇O2max. An ad-libitum buffet meal was consumed 1.5h after exercise. Blood samples were collected prior to altitude exposure and at 60, 135, 195, 240 and 285 minutes. No trial based differences were observed in any appetite related measure before exercise. Post-exercise area under the curve values for acylated ghrelin, pancreatic polypeptide and composite appetite score were lower (all P<0.05) at 4300m compared with sea-level and 2150m. There were no differences in glucagon-like peptide-1 between conditions (P=0.895). Mean energy intake was lower at 4300m (3728±3179kJ) compared with sea-level (7358±1789kJ; P=0.007) and 2150m (7390±1226kJ; P=0.004). Proportional reliance on carbohydrate as a fuel was higher (P=0.01) before breakfast but lower during (P=0.02) and after exercise (P=0.01) at 4300m compared with sea-level. This study suggests that altitude-induced anorexia and a subsequent reduction in energy intake occurs after exercise during exposure to severe but not moderate simulated altitude. Acylated ghrelin concentrations may contribute to this effect.