When temperatures soar, many people find their appetite suddenly plummets. The idea of eating a hot meal becomes the last thing our minds when the heat becomes too much to bear.
This doesn’t happen because the body is being fussy. The key reason why the simple act of eating becomes so unappealing to us in the heat largely has to do with the body working to keep running, and avoid overheating.
In order for our metabolism and many other physiological functions to perform correctly, the body needs to maintain an average internal body temperature of 37°C. Body temperature is tightly controlled by the brain’s temperature control centre, the hypothalamus.
If our internal temperature ever gets too low or too high, the action of enzymes and other biochemical reactions will stall or stop working properly. This is why it’s integral that average internal temperature is closely regulated.
Numerous factors can impact core temperature. These can include infections, exercise and exertion, hormones, alcohol and drugs.
The ambient temperature of the environment matters, too. So during hot weather, the body deploys several cooling mechanisms to prevent the outside heat from making core temperatures rise.
Sweating, for instance, helps us cool down. The body also flattens the hairs on the skin to prevent them from retaining heat.
Blood flow is paramount, too. When trying to cool down, warm blood is directed towards the skin so that heat can radiate from it and into the outside surroundings. This also means that blood flow is subsequently directed away from other areas of the body – including the gut.
After eating, blood is normally diverted to the gut, where it would be used in digesting, absorbing and transporting nutrients. But in hot conditions, the body is trying to shed warmth – not conserve it. Digestion adds to the workload, as well. The absorption, transportation and storage of nutrients all consume energy and generate heat.
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As such, the body suppresses gut blood flow and activity to dampen down these processes. This is one reason as to why appetite often plummets in the heat.
Heat and the gut
Our appetite is a balance between two opposing factors: hunger and satiety (the feeling of being full).
Part of this balance is driven by hormones – namely ghrelin (which makes you feel hungry) and leptin, PYY and GLP-1 (which make you feel full).
Some studies suggest that heat exposure can reduce ghrelin levels, while boosting satiety hormones – though results are inconsistent. It’s therefore unlikely that hormones are the sole contributors here.
There’s also an overlap between hunger and thirst. One can easily be mistaken for the other, as both are driven by the hypothalamus.
When it’s hot out and our body temperature rises, we sweat more to cool ourselves off. This means we lose more fluid and the mineral levels in our bloodstream fluctuate. To compensate and avoid dehydration, our brain triggers a feeling of thirst so we take on more fluids.
This thirst response also explains why we aren’t necessarily hungry when it’s hot, since we prioritise hydration over food. Although this helps to cool us down, drinking too much in one go we make us feel bloated, which can further discourage appetite.
This is why it’s better to prioritise lighter, low-temperature foods which are full of water – such as fruit, salad vegetables and light dairy products, including milk and yoghurt. High protein and carbohydrate-rich foods typically generate more metabolic heat when digested, which is precisely what the body is trying to avoid.
Heat stress also tends to cause the stomach to empty more slowly, which means we remain fuller for longer. The gut sends a message back to the brain as well, telling it that we’re full. This is another reason why you might feel bloated or full during the hot weather.
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The balance between heat and hunger is a dynamic one. In a heatwave, your body shifts its priorities – and cooling you down becomes much more important than digesting and absorbing a big meal.
But even when the heat is on, it’s good to remember that fuelling your body is still important. You may just need to shift your approach to top yourself up, and stay cool.
Cooling yourself down should help with appetite. Drinking plenty of water, avoiding excess physical activity, wearing loose-fitting clothes and applying cold packs can help you to cool down.
When approaching eating, try and have small, frequent meals with nutrient-dense components – particularly those which are rich in water and electrolytes to replenish what may have been lost in sweat.
Protein is still important to eat, too. Splitting it into smaller doses to consume throughout the day can help. Foods such as nuts, dairy, vegetables, pulses, avocados, olives and grains are all good energy-dense options – and feature heavily in many Mediterranean diets. They can help provide balanced nutrition, even when appetite is low and the heat is high.
Dan Baumgardt does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.