Acute exposure to a hot ambient temperature reduces energy intake but does not affect gut hormones in men during rest.

This study examined the effect of ambient temperature on energy intake, perceived appetite and gut hormone responses during rest in men. Thirteen men (age 21·5 (sd 1·4) years; BMI 24·7 (sd 2·2) kg/m2) completed three, 5·5 h conditions in different ambient temperatures: (i) cold (10°C), (ii) thermoneutral (20°C) and (iii) hot (30°C). A standardised breakfast was consumed after fasting measures, and an ad libitum lunch provided at 4-4·5 h. Blood samples (analysed for plasma acylated ghrelin, total peptide tyrosine-tyrosine (PYY) and total glucagon-like peptide 1 (GLP-1) concentrations), perceived appetite and thermoregulatory responses were collected throughout. Linear mixed models were used for statistical analyses. Ad libitum energy intake was 1243 (sd 1342) kJ higher in 10°C and 1189 (sd 1219) kJ higher in 20 v. 30°C (P = 0·002). Plasma acylated ghrelin, total PYY and GLP-1 concentrations did not differ significantly between the conditions (P ≥ 0·303). Sensitivity analyses for the 4 h pre-lunch period showed that perceived overall appetite was lower in both 30 and 10°C when compared with 20°C (P ≤ 0·019). In conclusion, acutely resting in a hot compared with a thermoneutral and cold ambient temperature reduced lunchtime ad libitum energy intake in healthy men. Suppressed perceived appetite may have contributed to the reduced energy intake in the hot compared with thermoneutral ambient temperature, whereas gut hormones did not appear to play an important role.