Humans evolved in environments that were rarely 72 degrees. We experienced temperature swings with the seasons.

In 1833, scientists theorized that exposure to the cold caused illness. Hence the term “catching a cold.” But it wasn’t until 120 years later that we realized occasionally being cold can be good for us.

JFK, Navy SEALs, and Ama Women

Something often forgotten in JFK’s famous “moon speech” is that he also called for “the Secretary of Defense to expand rapidly and substantially … special forces and unconventional warfare units.”

The US had experienced particular success with underwater demolition teams in World War II. Kennedy and his advisors wanted more of those water-centric warriors for the escalating conflict in Vietnam.

Eight months after Kennedy’s speech, the military established the first two Navy SEAL teams.

The problem: The American military didn’t know much about how the human body behaves when exposed to cold, deep water. So they looked to a curious group to understand the topic.

Starting around 10,000 years ago, women in the tiny fishing villages of Japan and Korea began diving into the cold waters of the Japan Sea and the Pacific Ocean.

No wetsuits. No breathing contraptions.

The women would strip down to a loincloth, diving trunks, or nothing at all.

They’d row or swim to a spot where the ocean’s rocky bottom was 10 to 90 feet below, and dive, scouring the cold, clear ocean depths for edible seafood like uni or mussels. People called these women the “Ama,” or “sea women.”

In the summer, the Ama worked six- to ten-hour days on the chilly water, doing more than 150 daily dives. From late fall to early spring, the ocean water dropped to just 50 degrees and the air temperatures could be just a couple of degrees above freezing. So they’d do a handful of dives, warm themselves near a bonfire on shore, then dive again.

The military sent 40 of the best physiologists from Japan, Korea, and the United States along the Pacific Coast to study the 18,000 Ama.

What We Learned From the Ama

The inquiry showed that the Ama had fewer incidences of 14 of the 16 illnesses the scientists studied.

Compared to their fellow villagers, the women were less likely to catch a cold, get heart disease, arthritis, liver or kidney diseases, and so on.

These results weren’t entirely attributable to the cold. Remember that other factors like swimming and spending all day in nature likely kept them healthy. For example, the Ama also had larger lung volumes, stronger muscles, and better endurance.

But the cold played a factor. And the results dispelled the old myth that the cold will lead you to catch a cold—quite the opposite.

The scientists also wondered how all that time in the cold impacted the Ama’s metabolisms.

A cold body, after all, ignites a complex network of calorie-burning internal furnaces to ensure that its organs don’t become dangerously chilled. So they picked, at random, 20 Ama and 20 villagers and invited them into a makeshift lab to have their metabolic rates tested.

The data showed that the Ama burned an additional 1,000 calories a day.

Research on the Ama would shape the future of combat diving. It helped the SEALs dive deeper, longer, and emerge from the surf ready to operate. But it also came with a lesson for the scientific community and you and me: We should probably expose ourselves to temperature swings.

The Case for Getting Cold

Thanks largely to the Ama research, scientists now know part of what’s driving the 1,000-calorie burn: brown fat. Brown fat is a metabolically active tissue. In the cold, brown fat acts like a furnace that burns our white fat (the type we try to lose with diet and exercise) to generate heat. This protects our vital organs from becoming too cold.

Which is precisely why a team of scientists in the Netherlands think getting comfortable with the cold can be an effective weight-control tactic. The bad news, the scientists say, is that our creature comforts have rendered brown fat moot. We now live at 72 degrees and rarely encounter extended temperature swings.

“In the past century, several dramatic changes in the daily living circumstances in Western civilization have occurred, affecting health. For example, we are much better able to control our ambient temperature,” wrote the scientists. “We lack exposure to varied ambient temperature [because we] cool and heat our dwellings for maximal comfort while minimizing our body energy expenditure necessary to control body temperature.”

Scientists call this burning of energy to stay warm “non-shivering thermogenesis.” Research shows it can elevate metabolism from a small percentage to 30 percent.

The scientists wrote, “Similar to exercise training, we advocate temperature training. . . . More-frequent cold exposure alone will not save the world, but [it] is a serious factor to consider.”

The cost of harnessing the power of brown fat is, of course, braving the cold.

But the scientists don’t think we have to go to extremes.

64 Degrees + More Time Outside

First: In winter, scientists recommend people lower their thermostats by three to four degrees each week. This slowly pushes our comfort zone, allowing us to adapt without unnecessary suffering. Then we can stop once we’re living in 64 degrees. Keeping the house at 64 degrees not only saves heating costs, it can also be beneficial for our health. It’s also an ideal sleeping temperature—and sleep improvements can lead to many health benefits.

Second: We should also spend more time outdoors this winter.

Ice baths are currently popular, and they probably benefit the people who enjoy them (oddly enough, people who hate them may not see the same benefits … I can write more on this, if you’re interested). But it’s hard to say if a few minutes in ice water is “enough” to get Ama-like results.

For most people, it’s better to prioritize time outdoors in the cold. Remember, the Ama weren’t getting cold in a tub at home—they were also outdoors and exercising.

The cold outdoors isn’t as intense as sitting in a tub of ice. But you’re exposed to the cold for longer—while also being physically active outdoors. And when you feel cold and want to quit, you can’t jump out of the tub and, like, drink a hot cup of coffee. You still have to brave the cold on the way back home.

Two Percent Top Two

My two favorite things this week ...

How Life Stress Tweaks Your Knees, Back, and Shoulders

​Researchers at the University of Missouri found that people are twice as likely to suffer an athletic injury during times of high life stress. The takeaway: During stressful times, it might be worth backing off of extreme training until your stress subsides. E.g., Don’t train extremely hard every day during a project deadline or at the end of the quarter.

A Useful Tool to Not Break Rule 2

Rule 2: Don’t die. I carry this Garmin InReach Mini GPS transponder when I go into the wilderness or kinetic environments. It's expensive, but so are funerals. The device allows me to map where I am so I don’t get lost, send short messages to my wife—”still alive!”—and send an SOS message to GEOS emergency response teams if things go wrong. If I’m not traveling, I keep the device in my truck (Garmin has plenty of wild stories about people who go off the road in areas without cell service and call for help).

Have a chilly week,

Michael

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Sponsored by GORUCK

When I decided to accept sponsorships for this newsletter, GORUCK was a natural fit. Not only is the company's story included in The Comfort Crisis, but I've been using GORUCK's gear since the brand was founded. Seriously. They've been around ~12 years and I still regularly use a pack of theirs that is 11 years old. Their gear is made in the USA by former Special Forces soldiers. They make my favorite rucking setup: A Rucker and Ruck Plate.