Increasing water intake influences hunger and food preference, but does not reliably suppress energy intake in adults.

Increasing water intake is often purported to reduce energy intake, and is recommended as a weight loss strategy. The few experimental studies that have been conducted to verify these claims have examined the impact of a single pre-load of water before a meal. Although correlational data indicate a relationship between hydration, energy intake, and weight status, there is very little experimental research in this area. The current studies examined the hypothesis that elevated hydration, through increased water intake, would suppress energy intake. In Experiment 1, participants (n = 49) were asked to consume either one, two, or three 500 ml bottles of water throughout the morning before a lunch buffet in the laboratory. When participants categorized as normal weight drank three bottles of water they consumed less energy at lunch, but there was no effect on participants categorized as overweight or obese. In addition, increased water intake suppressed liking of food items in all participants and hunger in females. A follow-up study (n = 45) was conducted to test if four bottles of water throughout the morning would result in a similar energy suppression in participants categorized as overweight or obese. Surprisingly, in the second experiment, there was no effect of water intake on energy intake at lunch in any of the conditions. There was, however, a similar suppression of hunger and food liking. In conclusion, increasing water intake throughout the morning only suppressed energy intake in individuals categorized as normal weight under certain circumstances, and had no effect on individuals categorized as overweight/obese.