Need to Know
  1. Americans frequently mistake dehydration for hunger
  2. Thirst and hunger send similar signals to your brain
  3. Stay hydrated throughout the day to avoid false hunger pangs

Do you feel like you’re always hungry? Or do you frequently want something to eat right after eating a full meal? You may be dehydrated, and your body may be misinterpreting those feelings of thirst as hunger.

Hunger and thirst seem like they should be two very distinct motivators that drive you to either eat or drink. Hunger = food = acquiring nutrients/energy, while thirst = water = hydration. But surprisingly, hunger and thirst trigger the same types of signals in your brain. Your hypothalamus, the portion of your brain responsible for controlling feelings of hunger and thirst, responds similarly whether you’re thirsty or you haven’t had enough to eat.

Both internal and external factors tell the hypothalamus when your body is hungry or thirsty. Those factors account for what we eat as well as how our diet is influenced by social context. For example, our brains are constantly accounting for things like what sort of containers food is served in or the amount of liquid that we expect in a traditional version of a dish. Then there’s the actual internal fact of what food is made of. Most foods contain some amount of water, and when they are metabolized by our bodies, they release their water content, mimicking how we process water when we’re drinking it.

It gets complicated fast. Think about what happens when we drink a beverage like a shake or a yogurt smoothie. Our bodies harvest nutrients from those foods and converts them into energy, mirroring how our body processes solid foods. Since the nutrients came in liquid form, however the hypothalamus can get confused. How does it know for sure if that smoothie satisfied thirst or hunger?

Here’s another example: imagine you had soup for lunch. Your brain could perceive that soup as a liquid meant to address your thirst. But it might not get enough water out of it to actually satisfy your thirst, so your brain keeps sending signals saying “I’m thirsty!” This might feel to you like hunger, even though it’s really a request for hydration. Or, maybe your brain processes this the other way around, seeing the soup as a hydration source but not a nutrient/energy producer. Not confused yet? Just wait: if you wanted to make things even more complicated, you could drink the soup out of a cup instead of eating it with a spoon. With so much influencing your brain both inside and out, you can see how signals might get crossed.

It’s easy to interpret all of the signals your hypothalamus sends as hunger; people often assume that hunger is the most powerful survival motivator. But studies have found that thirst motivations are more intense and constant throughout the day compared to hunger. Your body can only survive for about a week without water — which makes sense considering water makes up over 75 percent of the human body and is vital to healthy cell, tissue, and organ function — but it can last for almost a month with water but no food. Given that, it’s no surprise that feelings of thirst are typically much more urgent and intense than feelings of hunger. Plus, our bodies process water so efficiently that under normal circumstances the consequences of overdrinking are less bad than the consequences of overeating.

So, there’s the key danger of mistaking thirst for hunger. Your body’s drive to stay hydrated may actually push you to eat, and eat more than you need to, when really you should be drinking.

dehydration infographic

How can you tell if you’re truly hungry or if your brain is confusing its signals and you’re actually dehydrated? The best way to prevent signal misinterpretation is to drink water consistently throughout the day. At the very least, adults should be aiming for eight eight-ounce glasses of water (or just under two liters) per day — more if you’re above average height, moderately to highly active, or sweating due to heat/working out. Many recommendations are even higher. For example, the Institute of Medicine recommends a total fluid intake of three liters for men and 2.2 liters for women — a substantial portion of which should be water.

Still not sure whether that feeling is hunger or thirst? Here are three easy tests:

  1. Drink an eight-ounce glass of water, then wait 15 minutes for your nervous system to relay the message from your stomach to your brain that it has been satisfied. Still feel hungry? You’re more likely to actually need food.
  2. Note the last time you had something to drink that would keep you hydrated — things like coffee, soda, and energy drinks do not count. If it’s been a few hours, or you can’t remember when you last had water or a comparable hydrating beverage, try the drink-a-glass-of-water test before making a snack.
  3. Keep track of how much water you’ve had throughout the day (you can use an app like Waterlogged to do the counting). Imagine you’re shooting for 64 ounces a day. If it’s three p.m. and you’ve only had 24 ounces of water so far, there’s a good chance you’re thirsty, not hungry.

In the end, there’s generally no harm in reaching for a glass of water before you reach for a snack. Your body will thank you for the water and it won’t unintentionally trick you into consuming excess calories.