On hot summer days, you probably noticed that you are not so hungry – you want to eat less often than in cold weather, and the amount of food consumed becomes smaller. At the same time, there is less desire to consume heavy and fatty dishes, and more desire for vegetable salads and fruits. Scientists have long been studying the relationship between ambient temperature and appetite. In their opinion, a dulled feeling of hunger in hot weather is a normal phenomenon caused by our biological needs.
Most people want to eat less in hot weather. Photo source: kp.ru
Why temperature affects appetite
In cold weather, the human body requires many more calories than in hot weather to maintain normal body temperature. Let us recall that a calorie is a unit of energy. Burning energy allows us to generate heat, and thus prevents the body from cooling down. Accordingly, when we are cold in winter, there is a need to replenish the calories spent in greater quantities, so we want to eat more often and more food. Moreover, the choice often falls on high-calorie foods.
As the ambient temperature rises in spring and summer, the need for a large number of calories decreases, as other mechanisms for maintaining body temperature begin to turn on. During hot weather, for example, a person begins to sweat actively, resulting in an increased need for liquids, as well as salt and microelements that are washed out with sweat. Digesting food only takes away excess energy in the heat. Therefore, appetite gradually decreases.
In hot weather, the need for calories decreases, but more liquid is required. Photo source: unews24.ru
However, the mechanisms of this process are still not exactly clear. According to Matt Carter, a neurobiologist from Williams College in Massachusetts, calorie consumption is influenced by various factors – hormones, certain proteins, and environmental factors. They affect how and why we feel hungry.
As scientists explain, our body always strives to maintain stability of internal conditions, and this is called homeostasis. Body temperature and hunger are also homeostatic processes, so we feel hungry when the body is low on calories and feel full when we replenish our energy reserves.
How temperature affects hunger
Homeostatic processes in the body are usually supported by hormones. As we have already said, the feeling of hunger and satiety largely depend on two hormones – ghrelin and leptin. The first is produced when a person's stomach is empty, and the second is generated by fat cells and tells the body that it has enough food to consume.
The hypothalamus is responsible for the feeling of hunger. Photo source: eda.show
Hormones themselves, of course, cannot cause any feelings in our body, nor can they influence our behavior, but they serve as signals to the brain, or more precisely, to certain parts of it, such as the hypothalamus. As is known, it is responsible for hunger, maintaining temperature and thirst.
It has long been known that the lower part of the hypothalamus contains many specialized neurons responsible for feelings of hunger and satiety. As a result, the hormone ghrelin stimulates neurons that cause hunger (AgRP neurons), and at this moment we feel like we want to eat. Leptin suppresses hunger neurons and stimulates other neurons called POMC, which provide a feeling of fullness.
The brain has «temperature sensors» which influence feelings of satiety and hunger. Photo source: shkolazhizni.ru
However, it is not entirely clear how temperature affects the functioning of this system. It is now known that the brain has its own temperature sensors – these are certain proteins that change shape when the body temperature reaches a certain value. A study published in 2020 showed that in mice, certain brain cells activate hunger neurons when the ambient temperature is low, causing them to develop a strong appetite.
If the ambient temperature is too high, a certain protein is activated in satiety neurons (POMS), causing the feeling of hunger to disappear, according to another study published in 2018 in PLOS Biology. It would seem simple, but according to scientists, there are other mechanisms that work together.
During hot weather, you need to eat more light, low-calorie food. Photo source: lifehacker.ru
For example, sometimes these biological mechanisms may not work, and then a person experiences excessive hunger regardless of the ambient temperature. Sometimes, due to “failures”, a person may feel hungry even after his body is full. All this suggests that appetite is a complex balance influenced by a large number of factors, including the environment. Although it seems to us that the need for food and drink arises on its own, in fact, the brain takes into account the need for calories, fluids, takes into account body temperature and much more.
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But regardless of the feeling of satiety or hunger, in extreme heat we recommend eating a certain set of foods that we talked about earlier, and also drinking more water. This will allow you to reduce the load on your body and avoid negative consequences.