Abstract
Fluid ingestion is necessary for life, and thirst sensations are a prime motivator to drink. There is evidence of the influence of oropharyngeal stimulation on thirst and water intake in both animals and humans, but how those oral sensory cues impact thirst and ultimately the amount of liquid ingested is not well understood. We investigated which sensory trait(s) of a beverage influence the thirst quenching efficacy of ingested liquids and the perceived amount ingested. We deprived healthy individuals of liquid and food overnight (> 12 hours) to make them thirsty. After asking them to drink a fixed volume (400 mL) of an experimental beverage presenting one or two specific sensory traits, we determined the volume ingested of additional plain, 'still', room temperature water to assess their residual thirst and, by extension, the thirst-quenching properties of the experimental beverage. In a second study, participants were asked to drink the experimental beverages from an opaque container through a straw and estimate the volume ingested. We found that among several oro-sensory traits, the perceptions of coldness, induced either by cold water (thermally) or by l-menthol (chemically), and the feeling of oral carbonation, strongly enhance the thirst quenching properties of a beverage in water-deprived humans (additional water intake after the 400 ml experimental beverage was reduced by up to 50%). When blinded to the volume of liquid consumed, individual's estimation of ingested volume is increased (~22%) by perceived oral cold and carbonation, raising the idea that cold and perhaps CO2 induced-irritation sensations are included in how we normally encode water in the mouth and how we estimate the quantity of volume swallowed. These findings have implications for addressing inadequate hydration state in populations such as the elderly.