Hanoi has already reached 40 degrees celcius this summer. In an effort to cool off, I investigated the confusing system of foods that are considered "hot" and "cold" by Vietnamese tradition.

It's hot outside. Sweat trickles down your back, and the black glassy asphalt melts your rubber soles, slow-cooking your feet like a hot pot.

Downing a hot cup of tea might feel like the last thing you want to do in this kind of weather, but long before the advent of air conditioning, food and drink were used to stay cool. Even today, billions of people in India and China sip on hot cups of tea, despite the hellish temperatures of summer, to keep from overheating.

 

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Canh rau: A light soup made by boiling whatever extra greens are left over in the kitchen (usually rau gai, which is similar to chard, or mong toi, a Vietnamese spinach) with chicken or pork broth.

 

That's not just folklore at work. Western scientists have discovered that receptors on your tongue respond to hot substances, as well as the capsaicin in chili peppers, by forcing your body to perspire even more than you need, effectively cooling you down.

But while the science of sweat might be unequivocal, spicy foods and hot drinks aren't all equally cooling in the eyes of Asian tradition.

In Hanoi, where temperatures have already reached 106 degrees Fahrenheit this summer, I've been told that grapefruit, melon, soy, and fish are considered "cold." Mango, garlic, onion, guava, lychee, coffee, beef, and ice are "hot."

 

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Nom toi-bi ngo-ca rot: Garlic, pumpkin, and carrot salad with mint leaves.

 

It's the yin versus yang duality, one of the basic elements of traditional Chinese medicine. Stemming from Buddhist philosophy in India, it has influenced the medicinal traditions in much of Asia, from Pakistan and Nepal to here in Vietnam. Like many other things in life, food and drink are believed to have their yin (static, cooling) and yang (active, warming) qualities, too.

I've received a litany of commands already this summer. "Don't eat so much chili! You will make your body hot and have pimples!" Or "Go eat some grapefruit and chill out!" They weren't just talking about my temperature.

 

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Dau sot ca chua: Salted tofu cooked in an semi-acidic tomato sauce, with uncooked scallions added on top.

 

But the ad hoc food prescriptions and threats of various ailments quickly became overwhelming instead of enlightening, so I met with a local Vietnamese chef to get some clarity. Chef Nguyen Thi Minh, whose parents operated a famous restaurant in Hanoi for 60 years, told me, "We have to spend our life to know what is cold and hot, to get experience to know, to try this and that. I need to care for my customers' health, like the many pregnant women who come here."

Pregnant women and peaches apparently do not get on well. "In Vietnamese culture, the peach causes big problems with the mind and the brain," Huong declared strictly.

She insists that cooking must follow the weather. For the summer, she suggests fish and other seafood, along with white meats without their skin. I tried her Hanoi fried fish with parsley and scallion accompanied by bun noodles and a sweet vinegar fish sauce. I also tried her sautéed squid in lemongrass. Both were tasty and light, though I can't claim to have felt cold inside.

 

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Cha ca Ha Noi: Hanoi fish that's been grilled and then sautéed again in a pan with scallions and dill. It's served with cold bun noodles and a sweet lime fish sauce with dill and peanuts.

 

Despite what Western science knows about the tongue, Huong claims that food temperature doesn't affect yin and yang. "Pumpkin soup—hot or cold, does not matter," she said. "It is pumpkin, so it must cool." I tried a cooked pumpkin and carrot salad coated in sesame seeds and cloves of roasted garlic. The dish couldn't have tasted more like autumn, but it also felt light and summery.

In order to understand more about what makes a given food hot or cold in the Vietnamese tradition, I met with Nguyen Khac Chuong, a Vietnam-UNESCO recognized master martial arts teacher and student-practitioner of Eastern medicine at Tue Tinh, Vietnam University of Traditional Medicine. We spent two sweaty hours chatting over tea and plums under the porch of a traditional wood house at his martial arts compound.

It turns out that nothing is clear-cut. Processed tea in China may be yang while Vietnamese tea could be yin. Yang tea might become yin if eaten alongside a plum, or during the day (yang) rather than evening (yin). Depending on whether the tea is green or black, it moves through different body meridians (energy channels). Green foods go straight to our liver (remember for your summer hangovers).

 

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Vietnamese green tea (tra xanh Viet Nam) and mung bean porridge: mung been boiled in water with very little sugar added.

 

Water is generally yin, "but it depends on how you think about it—it could be yin or yang," Chuong riddled. He said the best thing to do in summer is to keep water balanced in your body. Don't do things that make you drip sweat, and avoid physical activity aimed at calorie burning, he told me. Try tai chi and putting energy back intoyour body, he suggested.

Feeling even more confused, I begged Chuong for some detailed advice. How can hot city-dwellers use food to stay cool?

"Eat for yourself in the morning; eat for your friends at lunch; eat for your enemy at night," he said. "Eat very little at night, eat what your wife cooks you, and search for balance. Do not be at war with yang; without yang, you don't have yin."

 

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Pyung yang naeng myun: chewy sweet potato or arrowroot noodles in a sweet vinegar broth with carrots, cucumber, pear, boiled and shredded egg, chicken and lean cuts of pork, and most importantly, spicy chili paste.

 

Later, with this enigma still in my head, I visited an official North Korean government-run restaurant in Hanoi, which is operated by walkie-talkie-toting North Korean ladies. They make a mean dish of cold spicy noodles, called pyung yang naeng myun, with vegetables and lean cuts of various meats. It is actually served in ice.

It was hot outside, and that felt pretty damn good.