A flatlay of a salad, tortilla wrap and a glass of water on a table.

Hungry or thirsty? Here’s why your body can’t mistake the two

Posted by for Wellbeing

You’ve been told you’re confusing thirst with hunger, but how true is that? In her latest Head Strong column, psychologist Kimberley Wilson debunks the myth that you can drink away hunger. 

Raise your hand if you’ve ever been told that you’re not hungry, you’re just thirsty.  * Sigh * This kind of ‘advice’ suggests that hunger is bad and that we all need to work harder to avoid and control it. Aside from the obvious issues of demonising food and the natural urge to fuel our bodies, the problem with this advice is that there’s no evidence to support it.

Hunger and thirst are different biological mechanisms so it’s actually very unlikely that they will be mistaken for one another. While a 2010 study found that we are actually more motivated to drink when we are thirsty than we are to eat when we are hungry – perhaps because of the more immediate risk to health from dehydration than hunger – the truth is that most of us aren’t even eating and drinking in response to hunger and thirst cues in the first place. Rather we tend to eat to time (eg eating because it’s ‘lunchtime’ even if you’re not yet hungry enough to eat), because food is available, or for psychosocial reasons like boredom, tiredness or to relieve stress.

It may be true is that some people are underhydrated, particularly the elderly. However, for most of us this is easily remedied. So the idea that your hunger signals are actually just dehydration, and that you can trick your body into thinking that you have eaten enough with water, is misguided.

Your stomach is, essentially, a stretchy bag full of acid and as you eat this bag expands. Nerves in the lining of the stomach recognise this expansion and send signals to the brain that the stomach is filling up. On receiving these messages the brain turns off the hunger signals and you feel satisfied. Now, there is some truth to this, but in reality, stretch receptors in your stomach are only a small part of the intricate story of how your body monitors and regulates hunger and satiety.

Eating to live

Your body evolved to carefully manage your overall energy balance for lots of very important reasons. First up, your brain has the highest energy consumption of any organ in the body. Much of your basal metabolic rate (BMR), the amount of energy that your body uses while at rest, is down to the brain. 

Secondly, the amount of energy available (and for women, especially glucose) indicates to the body whether the environmental conditions are safe to reproduce. Whether you want to have a child or not, what this means is that stress hormones, bone health and fertility are linked to energy availability. Additionally, unlike the rest of the body, the brain is unable to store energy. This makes the brain sensitive to information about the energy status of the body. To minimise the risk of life-threatening undernutrition, as well as stretch receptors in the stomach the body also has:

  • Texture and nutrient receptors in the mouth
  • Stretch receptors in the intestines
  • Nerves that sense nutrients (especially protein and fat) in the gut
  • Glucose-sensing cells in the pancreas
  • Satiety hormones produced by fat cells
  • Nutrient-sensing pathways – enzymes that respond to low glucose and protein levels
  • Hunger hormones that are released when your stomach is empty
  • Osmolarity monitoring – assessing the concentration of nutrients in the blood
A woman sat in her bed with a glass of water in her hand.
Are you hungry or thirsty? Here's why there's a big difference

Your brain coordinates all of this information (and more) with data on how much energy is being expended to dial up or down your hunger, satiety and metabolism.

Going back to our fabled glass of water; yes, drinking a big glass of water will activate the stretch receptors in your stomach, and this can dampen hunger at that moment. However, this water will be very quickly absorbed so it will not trigger stretch receptors in the intestines. It won’t set off the nutrients sensors in the mouth and gastrointestinal tract either, or turn on nutrient-sensing pathways. Before long your brain will realise that all it had was water and your hunger will come right back to previous levels, if not higher. In short, water won’t stop you from feeling hungry, but food will.

Can you drink hunger away?

All of these processes have evolved from history, when famine was a serious threat to life and the body adapted to do everything it can to help you to survive. In evolutionary terms, your body is much older and much smarter than you are. So maybe we need to have some respect. Why think that you could outsmart millions of years of scientific adaptation with a glass of water?

The wish to simply suppress hunger is often a sign of other concerns, such as body dissatisfaction or an attempt to maintain an overly restrictive diet (or both). You might be trying to adhere to external rules rather than respond to internal cues. If so, it may be more helpful to seek appropriate psychological or nutritional support.

That said, modern life presents the hunger-satiety system with some significant challenges. If you are struggling to regulate your food intake, it is more likely to be a problem of inputs into the system, rather than the system itself. For example, the type of food we eat has an effect on hunger and satiety cues, and there is growing evidence that ultra-processed foods are particularly unsatisfying (compared to fibre-rich whole foods) and easy to routinely overconsume.

It’s important to stay hydrated but there is no evidence that we confuse hunger and thirst and your body is not easily duped. It’s also important to remember that your brain and body need a constant supply of nutrients, especially during periods of physical or emotional stress. Therefore, most of us would be much better off focusing on overall diet quality than simple restriction.

Interested in picking up more simple and nutritious recipes? Make sure you check out the rest of our meal ideas in the SWTC library.

Images: Getty / Pexels

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Kimberley Wilson

Chartered psychologist Kimberley Wilson is our Head Strong columnist, one of our resident experts from the Strong Women Collective and author of How to Build a Healthy Brain. She’s passionate about caring for our mental health through evidence-based nutrition and psychological therapy – and loves discussing how you can train your mindset to become stronger in body and mind.

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