We all know we should exercise and eat healthy. But some argue we should also live more like early humans.

For decades we have been taught that physical health depends on eating well and exercising regularly. But some argue that may not be enough.

“The secret to cracking into our inner biology is as easy as leaving our comfort zones and seeking out just enough environmental stress to make us stronger,” writes journalist and anthropologist Scott Carney in his recent book, “What Doesn’t Kill Us: How Freezing Water, Extreme Altitude, and Environmental Conditioning Will Renew Our Lost Evolutionary Strength.”

By including this “equally important, but completely ignored, third pillar” in your daily routine, you can “achieve big results in very little time,” writes Carney.

The basic idea behind “environmental conditioning” is that for thousands of years humans lived without the comforts of the modern world — no central heating, no elevators, no thermal base layer clothing.

Early humans hunted. They gathered. They fled from predators trying to turn them into a quick snack. All while suffering through snowstorms, heat waves, flooding, thunderstorms, and often a lack of available food.

As a result, the human species adapted to survive better in those extremes. Today we still carry many of the same genes that helped us survive thousands of years ago.

Some think the latent abilities associated with our early adaptations remain untapped.

“There’s an entire hidden physiology in our bodies that operates on evolutionary programming most of us make no attempt to unlock,” writes Carney.

So what will you find when you unlock this physiological treasure trove?

Carney suggests environmental conditioning can help you reconfigure your cardiovascular system and combat autoimmune problems. And “it is a pretty darned good method for simply losing weight,” he writes.

In the book, it’s clear that Carney isn’t just a reporter standing outside in his warm-and-woolies with a cup of hot coffee in hand while he watches others gladly suffering for improved health.

Under the guidance of Wim Hof — a Dutchman who advocates a mix of environmental exposure and conscious breathing to gain control of our involuntary physical responses — Carney dives headfirst into this world of ice baths and shirtless climbs up snow-covered mountain peaks.

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For people who already push themselves hard — marathoners, triathletes, and Tough Mudders — the idea that being too comfortable could be bad for your health probably strikes a chord.

But can immersing yourself in the rawness of the natural world really improve your health?

There is some research to back this up.

A 2015 study in Nature Medicine found that 10 days of cold acclimation — spending up to six hours per day at 59°F (15°C) — boosted insulin sensitivity in eight men who were overweight and had type 2 diabetes. This change indicates a lessening of their disease symptoms.

Another study that year, published in the Journal of Clinical Investigation, showed that exposure to 63°F (17°C) for two hours per day for six weeks decreases body fat. This study included 51 healthy young male volunteers.

There is even a 2014 study that supports Hof’s method of using cold immersion and conscious breathing to voluntarily control the immune system, which has long been thought to be beyond conscious control.

Like the other two studies, this one published in the journal PNAS, included a small number of subjects, which concerns some researchers.

“For human variation studies, you really want to have a great deal more than that. Working with just 24 people keeps you from making any sort of correlations,” Jessica Brinkworth, PhD, an assistant professor at the University of Illinois who studies the evolution of immune function, told Healthline.

What’s missing from research in this area is larger randomized studies that compare what happens to people undergoing environmental conditioning for many weeks with a similar group going about their normal routine.

And studies that compare the benefits of environmental conditioning with other health interventions like aerobic or strength exercises, mindfulness meditation by itself, or a diet of whole foods.

Brinkworth also has concerns with how the media sometimes spins the results of small studies and “health gurus.”

“The notion that you can ‘maximize your immunological potential’ is ludicrous,” she said. “It’s not like weightlifting. And that’s the way that it sometimes gets presented.”

Under normal circumstances, our immune system “is always actively engaged,” said Brinkworth — it recalculates, reevaluates, and reorganizes itself all the time.

Some things can weaken the immune system — chemotherapy, damage to the bone marrow, untreated HIV infection.

This can also be caused by a deficiency in nutrients — like zinc, vitamin C, or protein — that the immune system needs to function properly.

Even extreme calorie restriction can affect immune function. This can happen by not eating enough food or by burning off too many calories through extreme exercise or extended exposure to cold temperatures.

“Immunity is the most expensive system we have. It costs a lot of calories,” said Brinkworth. “So it’s not very surprising that in endurance athletes and people who are doing extreme workouts, we see a down-regulation in immune function.”

There are two parts to the immune system. The innate immune system protects the body from pathogens in a nonspecific way. This includes immune cells like phagocytes and mast cells, but also the skin — which Brinkworth calls the “largest immunological barrier that you have.”

Then there’s the adaptive immune system — which includes T and B cells. When this part of the immune system encounters a specific pathogen, it produces an initial immune response, and remembers. If the body runs into this pathogen again, the immune system will respond more quickly and dramatically.

Brinkworth said that when the body is under stress — like during calorie restriction — it can turn down the adaptive immune response in order to save energy.

This has her concerned.

“You can make the argument that some of the stuff that Hof is suggesting is dangerous,” said Brinkworth, “because it would potentially lead to this drop-down in adaptive responses if you did it persistently.”

Read more: Treating pain with heat and cold »

Others echo her concerns.

“Why should we go to the extreme when we just need to engage in exercise?” said Ellen Glickman, PhD, a professor of exercise physiology, and a self-professed “moderation person.”

The Centers for Disease Control and Prevention (CDC) reports that in 2015 less than 21 percent of American adults met the Physical Activity Guidelines for Americans for both aerobic and strength training.

These guidelines are far from extreme — at least 150 minutes per week of moderate-intensity aerobic exercise, and muscle-strengthening activities two or more days per week.

Of course, some people are drawn to extreme activities for the “rush.” But that doesn’t mean less intense exercise isn’t good for you.

Glickman said that aerobic exercise can be “equally engaging” and offers many benefits, such as boosting cardiovascular health, improving overall health and well-being, burning calories, and increasing endorphins.

In addition, if you commute to an office every day, it might be hard to find time to take on the cold outdoors.

“I don’t see how the extreme fits into our health and well-being on a daily basis. Eating right and exercising does. Balancing caloric intake and caloric expenditure does,” said Glickman. “Extreme sports, extreme anything doesn’t. Moderation does.”

Of course, spending time outside can be beneficial even if you aren’t ice dunking or meditating in the snow in your underwear.

Many studies show that natural settings may improve short-term memory, relieve stress, reduce inflammation, and help you focus more.

Read more: How long to get in shape? »

In the modern world, cut off from nature, we sometimes forget that evolution and our past environments made the human species what it is today.

“Evolution shapes health. Health is the outcome of evolution,” said Brinkworth. “That’s absolutely true.”

She stressed that evolution should definitely guide how we treat diseases and help people stay healthy, “but it needs to be done informed with real biological information.”

Other scientists wonder whether or not living like early humans makes sense from an evolutionary perspective.

“The notion that we are adapted to a Pleistocene environment, while it may contain some element of truth, is unlikely to be a highly accurate description,” Kyle Summers, PhD, an evolutionary biologist at East Carolina University, told Healthline.

Near the beginning of the Pleistocene Epoch came the Paleolithic Era — which inspired the popular paleo diet. This era lasted from roughly 2.5 million years ago to 10,000 years ago and predates agriculture.

Summers said that while “substantial” change occurred to the human genome during the Pleistocene period, “there is also likely to have been a significant amount of evolutionary change during our more recent evolutionary history, including the 10,000 years or so since the origins of agriculture.”

Add to that the challenge of knowing exactly how early humans lived, said Summers, “making any inferences about exactly what environment humans adapted to even during the Pleistocene highly speculative.”

And human populations lived in vastly different environments around the globe, which can make a big difference to health.

“Latitude, seasonality, social environment, and climate all affect immune function,” said Brinkworth.

Hof’s methods focus on cold environments. Humans living in tropical areas for thousands of years, though, may have different gene variants or physiological responses to cold than people from northern latitudes.

There are other factors that shaped the human species, as well.

In particular, said Brinkworth, infectious pathogens are the “number one driver, as far as we can tell, of immune function.”

Environmental conditioning has its proponents, but others caution a healthy dose of skepticism.

“While I think ideas from the paleo community may have some merit in some contexts,” said Summers, “it is hard to separate the valid ideas from those that are too speculative and unsupported.”

There’s also the risk of going too far. Being too much like a Paleo human may not be all that it’s cracked up to be.

“If you want to be living in rough circumstances and deliberately stressing yourself long-term and avoiding modern medicines and modern concepts of hygiene,” said Brinkworth, “you’re going to have the same lifespan as other members of the [early] Homo genus — that’s 30 to 35 years.”