During the sweltering summer months, we often notice that hunger strikes much less frequently than in cooler weather.
Researchers have long studied the impact of temperature on appetite. “We know that in colder conditions, people consume more calories,” said Allison Childress, a registered dietitian and assistant professor at Texas Tech University. She says there’s a basic biological reason for this.
What Is Hunger For?
Calories are a unit of energy; burning them generates heat, helping people endure cold weather. However, as winter transitions into warmer seasons, people notice that they feel less hungry, Childress told Live Science in an interview. The mechanisms behind this phenomenon are not fully understood. Childress says many factors influence calorie consumption.
Matt Carter, a neurobiologist at Williams College in Massachusetts, agrees. Hormones, proteins, and environmental factors all affect hunger and why it fades on hot days, he explained.
Our bodies are constantly striving to maintain stable internal conditions, a process known as homeostasis. This is why we sweat under the blazing sun or drink water after an intense workout. Hunger is also homeostatic: it signals when our bodies are low on calories. When we are full, hunger indicates that we have enough calories. Thus, our internal physiological state is balanced.
Many homeostatic processes are supported by hormones that act as chemical messengers in the body. Two key hormones for appetite and satiety are ghrelin, released by the stomach when it’s empty, and leptin, secreted by fat cells to inform the brain about fullness.
These hormones send signals to the hypothalamus, a part of the brain that regulates aspects such as body temperature, hunger, and thirst. In the lower hypothalamus there’s a mass of specialized neurons responsible for feelings of hunger and fullness, Carter noted. There, ghrelin stimulates AgRP neurons associated with hunger, making us feel hungry. Conversely, leptin suppresses these neurons and activates POMC neurons, which signal satiety.
Proteins as Temperature Sensors
Still, how temperature influences this complex system remains an open area of research, Carter said. The brain contains temperature sensors—proteins that change shape when the body reaches a certain level of heat. A study published in the journal eLife in 2020 showed that specific brain cells in mice provide information to AgRP neurons when temperatures are low, enhancing the feeling of hunger.
On the flip side, when the heat is on outside and our body temperature rises, a heat-sensitive protein in POMC neurons gets activated, which then stimulates neurons associated with the sensation of fullness. This mechanism was uncovered in a 2018 study published in PLOS Biology.
Childress says that, regardless of the body’s signals, it’s crucial to stay hydrated during the summer. Drink enough water and eat water-rich foods like fruits and vegetables. Frozen treats can raise body temperature because they often contain a lot of calories.
Overall, appetite is a complex tool that helps our bodies sync with the environment, Carter concluded.
