Effect of hydration status and fluid availability on ad-libitum energy intake of a semi-solid breakfast

This study investigated the effects of hydration status and fluid availability on appetite and energy intake. Sixteen males completed four 24 h trials, visiting the laboratory overnight fasted on two consecutive days. Standardised foods were provided during the 24 h and on day two an ad-libitum semi-solid porridge breakfast was provided. Water intake during the 24 h (0 or 40 mL·kg^-1) and fluid provision during the ad-libitum breakfast were manipulated so subjects were euhydrated with (EU-F) and without fluid (EU-NF) available at breakfast; and hypohydrated with (HYPO-F) and without fluid (HYPO-NF) available at breakfast. Blood samples (0 and 24 h), urine samples (0-24 h) and subjective responses (0, 24 and 24.5 h) were collected. HYPO trials decreased body mass by ~1.8%. Serum and urine osmolality increased and plasma volume decreased during HYPO trials (P < 0.001). Total urine output was greater during EU than HYPO trials (P < 0.001). Ad-libitum energy intake was not different between trials: 2658 (938) kJ (EU-F), 2353 (643) kJ (EU-NF), 2295 (529) kJ (HYPO-F), 2414 (954) kJ (HYPO-NF), (P = 0.131). Fluid intake was ~200 mL greater during HYPO-F than EU-F (P < 0.01). There was an interaction effect for thirst (P < 0.001), but not hunger or fullness. These results demonstrate that mild hypohydration produced by inadequate fluid intake and fluid availability during eating does not influence ad-libitum energy intake of a semi-solid breakfast, at least in healthy young males.