If you pay attention to news about nutrition, you’ve probably heard or read that people often mistake thirst for hunger–eating instead of drinking when they’re thirsty. Just do an online search using the words “mistake thirst hunger” and you will be directed to dozens of articles containing passages like this one:
Thirst occurs when your body needs water. When you do not drink enough water, your body receives mixed signals on hunger. Dehydration causes you to believe you need to eat when you really need liquid intake.
As a society, we have become so accustomed to being exposed to scientific findings that surprise us and contradict our experience that it is easy to just accept the idea that humans don’t know the difference between their two most fundamental and important perceptions with a shrug. But think about it for a moment: Does hunger (rumbling stomach, etc.) feel even remotely similar to thirst (parched throat, etc.)? Could the evolutionary process that developed these perceptions possibly be so flawed that all animals that possess them — not just humans but also, say, wild prairie dogs — are wandering around utterly confused about when to eat and when to drink?
Let’s Go to The Science
One thing that is clearly missing from the many articles telling us that people commonly mistake thirst for hunger is any kind of reference to published science proving that this is in fact that case. And there’s a reason. “I’m not aware of any evidence that’s the case,” says Stephen Guyenet, an obesity researcher who studies how the brain controls appetite.
However, the absence of proof that people eat instead of drinking when they’re hungry does not constitute proof that people drink when they are thirsty, or that they drink when they’re dehydrated and truly need fluid. There is, in fact, a big difference between humans today and wild prairie dogs, and it has to do with environment. Whereas prairie dogs still live in environments that are more or less the same as the ones they evolved in, we do not. This is important, because thirst and hunger are not completely innate — they are also influenced by environment — and there is evidence that our modern environment has weakened the links between hunger and eating and between thirst and drinking in ways that aren’t good for us.
In a study published in the Journal of the American Dietetics Association in 2009, scientists at Purdue University asked volunteers to rate their hunger and thirst levels every hour and to record their eating and drinking schedules for an entire week. The researchers found that the volunteers seldom ate when they were hungry or drank when they were thirsty. Instead they simply ate when they normally ate and also drank when they ate. Seventy-five percent of their fluid consumption occurred during meals.
The authors of this study speculated that, in primitive times, hunger and eating and drinking and thirst were much more tightly coupled, but that modern environmental factors such as cheap and plentiful food and calorie-counting beverages (the subjects got the majority of their fluid from such beverages) have weakened these connections.
There is also evidence that the types of foods we tend to eat today affect our thirst mechanism, making it less reliable as a cue to drink. A 2009 study by Australian scientists reported that subjects who included more high-fat and high-sugar foods in their diet exhibited weaker thirst sensitivity than did those who ate fewer of these foods.
So, what does all of this science mean on a practical level? Your goal, as it relates to fluid consumption, is to drink enough to stay consistently well hydrated day in and day out. Eating fewer high-fat and high-sugar foods and drinking fewer calorie-containing beverages may help you achieve this goal by making your thirst a more reliable indicator of your fluid needs.
But there’s only so much you can do to alter your environment. So it’s a good idea to get in the habit of drinking water fairly regularly throughout the day. Consumer products that enable people to accurately track their hydration status in real time may also be part of the solution.
Harshaw C. Alimentary Epigenetics: A Developmental Psychobiological Systems View of the Perception of Hunger, Thirst and Satiety. Dev Rev. 2008 Dec 1;28(4):541–569.
McKiernan F, Hollis JH, McCabe GP, Mattes RD. Thirst-drinking, hunger-eating; tight coupling? J Am Diet Assoc. 2009 Mar;109(3):486–90. doi: 10.1016/j.jada.2008.11.027.
Brannigan M, Stevenson RJ, Francis H. Thirst interoception and its relationship to a Western-style diet. Physiol Behav. 2015 Feb;139:423–9. doi: 10.1016/j.physbeh.2014.11.050. Epub 2014 Nov 20.