Why Eat Hot Soup on the Hottest Day? The Science of Fighting Heat with Heat

On the hottest day of the year, imagine two things set in front of you: a tall glass of iced drink, and a bowl of steaming-hot ginseng chicken soup. Which one does your hand reach for? Common sense says the cold one, obviously — yet across Korea and much of East Asia there’s an old wisdom that says the opposite. On the hottest days, eat the hottest thing. It’s called 以熱治熱 — “fight heat with heat.”

This seemingly backwards custom turns out to have read the body’s thermoregulation with surprising accuracy. Modern science is now explaining, piece by piece, exactly why.

The Dog Days and “Fighting Heat with Heat”

Korea has a seasonal tradition called 三伏 (Sambok) that divides the hottest stretch of summer into three markers: early, mid, and late “bok” days. Falling across the solar terms of Minor Heat (小暑) and Major Heat (大暑), this is the most sweltering period of the year — and it was precisely then that people made a point of eating not cold food, but hot ginseng chicken soup and other restorative dishes.

The reasoning comes from an old view in traditional Korean medicine. It held that in summer the body’s surface runs hot while its core actually turns cold. Heavy sweating drains your energy, and constantly eating cold things chills the stomach further, weakening digestion. So the logic of “fighting heat with heat” was to warm and nourish the core with hot, nutritious food.

Of course, “a cold core” isn’t the language of modern physiology. But the observation beneath it — that chasing only cold things in high summer can actually harm you, and that warm food aids recovery — holds up remarkably well under modern science.

The Science Behind “the Coolness of Hot Things”

The first key is sweat. Capsaicin in spicy food, or a bowl of hot broth, warms the body momentarily and makes you sweat. And the body’s single most powerful cooling system is precisely the evaporation of that sweat. As sweat evaporates off the skin, it carries away body heat and genuinely lowers your temperature. You make yourself briefly hotter by eating something hot, and the sweat it draws then cools you as it evaporates. There’s a reason so many hot-climate cultures developed spicy cuisines.

The second key is how digestion changes in the heat. Recent research shows that when the temperature rises, the body prioritizes shedding heat and reduces blood flow to the gut. Digestive activity slows and appetite drops — the heat-sensing proteins in the brain’s hypothalamus can even manufacture a feeling of fullness on their own. With digestion running weak like this, loading up on cold, heavy food burdens the stomach. Warm, easily digestible protein-based food, by contrast, goes down far more gently on a weakened summer gut.

The third is replacing what sweat takes away. In high summer, water, electrolytes, and energy keep draining out through sweat. A warm, protein-rich broth like ginseng chicken soup acts as a recovery meal, restoring what was lost.

So It Was Never Superstition

Put together, “fighting heat with heat” was a wisdom aimed at two things at once: cooling the body by drawing out sweat that then evaporates, and protecting and restoring a heat-weakened digestive system with warm, gentle nourishment. Our ancestors didn’t know words like capsaicin or hypothalamus, but through long experience they had read precisely how the body responds to heat.

Summer Heat Care You Can Practice This Year

Applied in modern terms, the principle looks like this.

• Don’t live on cold things alone: Trying to get through the heat on nothing but iced water and ice cream tends to leave digestion sluggish. Balance the cold with the warm.
• Warm, easily digestible protein: It doesn’t have to be ginseng chicken soup — any warm broth dish or gentle protein food suits a weakened summer gut well.
• Small and frequent: In the heat, eating small amounts several times a day burdens the body less than one large meal.
• Mind your water and electrolytes: What sweat takes out isn’t fully replaced by water alone. Broth-based foods and electrolyte-rich foods help.
• Use a little heat from spice: Spicy food that draws a light sweat can aid temperature regulation — but go easy if your stomach is sensitive.

Frequently Asked Questions

Does hot food really cool you better than cold food in summer?
Not “instantly cooler,” but through evaporative cooling from sweat it can lower your body temperature a little while later. Cold food feels refreshing in the moment but can burden digestion or leave you more sluggish on the rebound. The balance between the two is what matters.

Do you have to eat restorative dishes like ginseng chicken soup specifically in summer?
Not only in summer, but it’s clear that a warm, protein-rich restorative meal helps recovery in summer, when sweat drains so much of your stamina. There’s real experiential reason behind the tradition of eating it on the dog days.

Is it scientifically true that spicy food is good in the heat?
There’s a basis for it: capsaicin induces sweating, which aids evaporative cooling. That said, individual tolerance varies widely and it can burden a weak stomach, so enjoy it in moderation.

Is losing your appetite in summer normal?
Yes, it’s a normal physiological response. As the body prioritizes shedding heat, blood flow to digestion and appetite both decline. So rather than forcing large meals, it’s better to eat easily digestible food in small, frequent portions.

Closing Thought

The sight of someone sitting down to a steaming bowl of soup on the hottest day of the year might look, at a glance, like the stubbornness of a person too worn out by the heat to think straight. But inside that single bowl sat the body’s own principles — sweat and evaporation, digestion and recovery — held together whole. Our ancestors knew it through the senses rather than the language of science, and science is only now nodding along. On the hottest day this summer, try meeting that hot bowl not as superstition, but as one of the oldest prescriptions there is.