Numerous factors, including hormones, proteins, and the environment, influence how and why people feel less hungry when it’s hot outside.
Scientists have long studied the effects of temperature on appetite. “What we know is that people in colder environments tend to consume more calories,” says Allison Childress, a nutrition expert and associate professor at Texas Tech University. There is a biological reason for this: calories are a unit of energy, and burning calories can release heat, helping people maintain their body temperature in cold weather.
But as winter fades and the weather warms up, people often find themselves feeling significantly less hungry. The scientific community still doesn’t fully understand the exact mechanisms behind this phenomenon. According to Childress, multiple factors influence calorie intake.
Matt Carter, a neuroscientist at Williams College in Massachusetts, concurs. He explains that many variables—ranging from hormones and proteins to environmental factors—affect how and why people experience hunger, as well as why this sensation diminishes in the heat.
The human body constantly strives to maintain internal stability, known as homeostasis. This is why we sweat under the scorching Sun or drink water after strenuous exercise. Hunger is also a form of homeostasis. We feel hungry when our bodies are low on calories and full after eating.
Many homeostatic processes are maintained by hormones, which act as the body’s chemical messengers. Two key hormones, ghrelin and leptin, play significant roles in hunger and satiety. Ghrelin is released by the stomach when you’re hungry, while leptin is secreted by fat cells to signal the brain that you’re full.
These hormones influence human emotions and behaviors by signaling the hypothalamus, a brain region responsible for regulating aspects like body temperature, hunger, and thirst. According to Carter, a specialized cluster of neurons at the base of the hypothalamus orchestrates feelings of hunger and fullness. Here, ghrelin stimulates hunger-associated neurons called AgRP, whereas leptin inhibits them and activates POMC neurons, inducing satiety.
However, the impact of temperature on this complex system remains a topic for further research. The brain has temperature sensors, proteins that change shape when the body reaches certain warmth levels. A 2020 study in the journal eLife found that in mice, some brain cells relay information to AgRP neurons at lower temperatures, increasing hunger.
Another study published in PLOS Biology in 2018 discovered that POMC neurons possess a type of temperature-sensing protein activated by rising body temperature. Yet, Carter notes that other neural circuits might also coordinate to affect the amount of food people consume.
“Humans have biological mechanisms and temperature effects, but it’s crucial to understand that we can override these mechanisms,” Childress says. Sometimes, people lose the ability to heed their body’s signals, such as overeating past satiety or not eating when hungry.
Childress emphasizes the importance of staying hydrated during summer, either by consuming water-rich foods like fruits and vegetables or drinking water directly. Contrary to what one might think, frozen treats like ice cream can actually raise body temperature due to their high calorie content.
