Thirst, hunger or sweetness? What motivates humans to drink in the modern beverage environment?

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)


Physiological fluid balance is strictly regulated, yet much of our drinking occurs irrespective of fluid balance. The addition of palatable beverages to our diet encourages drinking for the enjoyment of taste. The emphasis on hydration in our society, “Drink at least eight glasses of water a day”, encourages drinking to prevent future thirst. The custom of consuming a beverage with a meal encourages drinking to wash food down or complement the flavours in the meal. The frequency with which drinking occurs irrespective of fluid balance may have led to the disassociation between thirst and drinking. In turn, individuals may believe they are thirsty (i.e., in physiological need of water) when they are simply responding to habit or reward.

It has been suggested that the low satiety of sugar-sweetened beverages leads to increased intake and consequently weight gain. However, evidence of the satiety of beverages is mixed and points to a range of sensory, cognitive, and physiological factors. Previous research has focused on the properties of liquid calories. Therefore, the subsequent experiments shifted the focus from the static properties of beverages to the dynamic motivations of the individual.

A field-based qualitative study generated theories about thirst, drinking, and beverage choice. Two laboratory-based studies measured intake of water, a reduced-sugar sweetened beverage or a sugar-sweetened beverage when participants (Study 1, N = 32; Study 2, N = 66) were both hungry and thirsty (only Study 1), hungry, thirsty, and neither hungry nor thirsty. Two online-based studies measured beverage choice (N = 166) and intake (N = 98) in the context of a meal. Choice and intake of water, a reduced-sugar sweetened beverage, and a sugar-sweetened beverage were assessed with 100 kcal, 300 kcal, 500 kcal, 700 kcal, and 900 kcal portions of food. These experiments raised questions about how drinking behavior may depend on the nature of thirst, and about reward underlying drinking behavior. Therefore, a final laboratory-based study (N = 26) investigated beverage reward and its ability to predict beverage intake, and if intake of water depended on whether the individual simply feels thirsty or undergoes physiological changes to fluid balance.
Date of Award25 Sept 2018
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorDanielle Ferriday (Supervisor) & Peter J Rogers (Supervisor)

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