When It’s This Hot, What Should You Eat?

As temperatures continue to climb, summertime is all about finding any way to stay cool. And that includes turning to foods that will hopefully provide a little relief. While not a panacea for the heat, body-cooling foods and no-cook diets could help to lower body temperature and make heat waves a little more bearable.

Living safely in consistently hot climates means staying hydrated, especially with chilled drinks or fruits. But there are other, more physiologically based—and even surprising—ways to make your diet more heat friendly. While the science behind diets, nutrition, and climate is still growing, changing global temperatures makes understanding the link between food and metabolism increasingly critical.

The contradictory cooling effect of spicy foods

One place to start is to explore how heat influences diets in warmer parts of the world. Why, for example, do the spiciest foods come from the hottest places on the planet? Think southeast Asian curries and peppers, and South American chilis. If spicy foods make you sweat and feel even hotter, why are they such a staple in warmer regions?

There’s a biological reason for that, says Dr. William Li, a former Harvard Medical School faculty member who has written a book about finding the right diet for your metabolism. What happens when you dig into a spicy dish? Your heart beats a little faster, you breathe a little harder, you start to perspire, and not just your mouth but your whole body can feel as if it’s on fire. And if you’re eating this dish and it’s above 90°F outside, you’re really feeling the heat.

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But sweating is the body’s physiological response to being too hot. “Our sole means of cooling is to sweat,” says Dr. Linda Shiue, an internist and chef who is director of culinary and lifestyle medicine at Kaiser Permanente San Francisco. Once you sweat, the perspiration evaporating moisture cools the skin. We’re not talking tens of degrees here—it’s fractions of single digits of change in temperature—but it’s still something. If the body’s core temperature starts climbing—which it does if you’re exposed to extreme heat for too long—sweating cools off the skin in an attempt to bring that core temperature down. Eating spicy foods jumpstarts that process, which is why they’re so popular in hotter regions of the world.

“Cultures in these parts of the world have known this for thousands of years,” says Li. “Their culinary culture triggers a hard-wired system that opens your pores and releases heat from the body. You feel temporarily hotter but that’s part of the package of cooling down.”

That hard-wired system involves a protein on our cells called TRPV1, which acts as a receptor for the active agents in spicy foods, such as capsaicin and capsinoids. The cells that have the highest concentration of TRPV1 receptors are on the tongue and the front of the roof of the mouth. Those spice agents trigger the receptors to send signals to the brain to release norepinephrine, a neurotransmitter primarily responsible for launching the fight-or-flight response. When this hyper-alert response is triggered, the body releases heat by triggering the sweats. That was helpful to human ancestors trying to outrun potential predators thousands of years ago…and also turns out to be useful in adapting to climate change today.

There are a bunch of foods and spices that can activate TRPV1. In addition to hot peppers, sweet peppers and black pepper can also stimulate the receptor. Garlic can as well, through a different chemical called diallyl sulfide, which doesn’t produce the same spicy sensation in the mouth but has the same end effect of activating norepinephrine and generating perspiration. Ginger and galangal, another root vegetable with a sharp, citrusy taste, are other foods—also commonly used in hotter regions—that can cause the same sweating and cooling effect.

Read more on extreme heat:

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• The difference between heat stress, exhaustion, and stroke
• The art of air conditioner maintenance
• Extreme heat hits companies where it hurts

It’s not just spicy foods that can cool

There are also other, less obvious foods that work on TRPV1, but the data supporting how they are connected isn’t solid enough yet. There is anecdotal data suggesting, for example, that fruits such as durian and pineapple can help to cool, but in different ways. Durian may activate TRPV1 and generate perspiration, while an enzyme in pineapple called bromelain can slow digestion, which reduces the amount of energy, and therefore heat, generated by that process. In Mexico, says Shiue, people often season their helpings of fruit—which are helpful for staying hydrated when the weather is warm—with tajin, a blend of dried chilis, lime juice, and salt. Another popular seasoning in the region is chamoy, made from pickled fruit and chilis. “How brilliant is this as a way to keep yourself cool as well as hydrated?” she says. In India, known for its long periods of hot days, the beverage of choice is nimbu pani, a mix of lemon or lime juice, salt, and sugar that not only cools but replaces electrolytes lost when the body is over heated.

Early data from animals also suggests that cinnamon can lower the stomach’s temperature by decreasing the amount of acid and enzymes secreted by cells, which can cool the body by as much as 2°C. More conflicting data suggests that ingesting or smoking CBD could produce the same ‘flushed’ feeling and generate perspiration similar to the way spicy foods can, but more research is needed to verify this body-cooling effect..

Metabolically, there’s another way that the TRPV1 system helps to keep the body cool that’s also counterintuitive at first. TRPV1 can burn brown fat, which is more abundant in newborns but is still present in adults, primarily in the neck, upper chest, and under the arms. In colder climates, people burn more of this brown fat because it’s a super-efficient way to generate body heat. That’s because in order to generate more heat, brown fat works together with white fat—the more common form of fat that people gain with age as their metabolism slows down—and starts using it as fuel. So when the body’s core temperature really starts to rise, brown fat can kick in to counterintuitively make people sweat even more, in an effort to cool down.

Calories and cooling

Looking more broadly, Li says there are other ways that people might adapt their eating as the world warms. Cutting back on daily calories can lower core body temperature, since when your body processes calories, it generates energy and heat. A 2011 study showed that reducing daily calorie intake by 23% can lower body temperature by under half a degree celsius. That may not sound like a huge drop, but when combined with other strategies, could help prevent heat stroke and related issues.

Intermittent fasting can also lower body temperature by triggering the body to burn calories differently. When we eat, we produce insulin to help break down those calories or store them as fat. During fasting, the body starts delving into those fat deposits for energy—in a way that generates less heat than the insulin-creating process. The body may be taking advantage of this strategy during extremely hot periods; when it’s uncomfortably hot, most people’s appetites start to wane, and this may be a physiologic coping mechanism for surviving the heat. “The body does anything it can to minimize the intake of energy and the generation of more heat, and that includes eating,” says Shiue. That’s not to say that fasting is a solution to keeping cool, since whatever small temperature benefits that come with it must be balanced with the potential dangers of becoming malnourished.

The science of how the human body’s energy needs change with heat, and therefore how heat affects things like how much and what people eat, is still in its early stages. But the latest studies on receptors like TRPV1 could help the world adapt to climate change as temperatures keep rising. “As we better understand how foods in certain cultures have been beneficial in cooling, I think it would be natural to adapt some of those ingredients in the culinary style of eating of the western world,” says Li. Shiue agrees. “If people know that yes, certain ways of eating have a function such as cooling the body, then maybe they will start to creep into our daily food choices,” she says. Which would make diets one more aspect of human existence that could be forever transformed by climate change.