The influence of angiotensin converting enzyme and bradykinin receptor B2 gene variants on voluntary fluid intake and fluid balance in healthy men during moderate-intensity exercise in the heat.

Angiotensin converting enzyme (ACE) and bradykinin receptor B2 (B2R) genetic variation may affect thirst because of effects on angiotensin II production and bradykinin activity, respectively. To examine this, 45 healthy Caucasian men completed 60 min of cycle exercise at 62% ± 5% peak oxygen uptake in a room heated to 30.5 ± 0.3 °C with ad libitum fluid intake. Blood samples were collected pre-, mid-, and immediately post-cycle. Fluid intake, body mass loss (BML), sweat loss (determined via changes in body mass and fluid intake), and thirst sensation were recorded. All participants were genotyped for the ACE insert fragment (I) and the B2R insert sequence (P). Participants were homozygous for the wild-type allele (WW or MM), heterozygous (WI or MP) or homozygous for the insert (II or PP). No differences between genotype groups were found in mean (±SD) voluntary fluid intake (WW: 613 ± 388, WI: 753 ± 385, II: 862 ± 421 mL, p = 0.31; MM: 599 ± 322, MP: 745 ± 374, PP: 870 ± 459 mL, p = 0.20), percentage BML or any other fluid balance variables for both the ACE and B2R genes, respectively. Mean thirst perception in the B2R PP group, however, was higher (p < 0.05) than both MM and MP at 30, 45, and 60 min. In conclusion, the results of this study suggest that voluntary fluid intake and fluid balance in healthy men performing 60 min of moderate-intensity exercise in the heat are not predominantly influenced by ACE or B2R genetic variation.

The effect of hydration status on appetite and energy intake.

This study investigated the effect of hypohydration produced by exercise and sub-optimal rehydration on appetite and energy intake. Ten males lost ~2% body mass through evening exercise in the heat (35°C). Over the next 13 h, participants were re-fed and either rehydrated (RE: water equal to 175% of body mass loss (BML)) or remained hypohydrated (HYPO: 200 ml water), until the following morning. Urine samples, blood samples and subjective feelings were collected pre-exercise, post-exercise and 13 h post-exercise, with an ad libitum breakfast provided 13 h post-exercise. Total BML at 13 h post-exercise was greater during HYPO (2.8 (0.5)%) than RE (0.5 (0.5)%). Energy intake at the ad libitum breakfast was similar between trials (RE: 4237 (1459) kJ; HYPO: 4612 (1487) kJ; P = 0.436), with no difference in energy consumed in foods (P = 0.600) or drinks (P = 0.147). Total water ingestion at the ad libitum breakfast meal was greater during HYPO (1641 (367) ml) than RE (797 (275) ml) (P < 0.001), with this being explained by increased water intake through fluids (P < 0.001). Thirteen hours post-exercise, participants reported greater thirst (P < 0.001) and lower fullness (P < 0.01) during HYPO. Alterations in hydration status produced by exercise are unlikely to influence post-exercise food intake and consequently other aspects of recovery or adaptation.