Become a Member

Get access to more than 30 brands, premium video, exclusive content, events, mapping, and more.

Already have an account? Sign In

Become a Member

Get access to more than 30 brands, premium video, exclusive content, events, mapping, and more.

Already have an account? Sign In


Diet & Nutrition

What is the Keto Diet and Should You Try It?

Everyone is talking about the keto diet. Our expert, Jonny Bowden, breaks it all down for you.

Heading out the door? Read this article on the new Outside+ app available now on iOS devices for members! Download the app.

Let’s just get this out of the way, shall we? The keto diet is a high-fat diet.

Those who advocate for ketogenic (keto) diets basically suggest that we reject the dietary guidelines of the past 40 years and embrace fat—yes fat, the one macronutrient we’ve been trying to avoid for decades. They’re suggesting that we turn the conventional wisdom about high-carb, low-fat diets on its proverbial ear. They’re telling us that the foods we were taught were great—cereals, breads, whole wheat pasta—are actually not, while the foods we were told were not good—animal products and fats—actually are.

Healthy tip!

On the keto diet, consume high-quality fats such as coconut oil, grass-fed butter, ghee, MCT oil, or avocado oil.

What is ketosis?

First, some definitions. The “keto” in ketogenic refers to ketones (also known as ketone bodies), which are a byproduct of fat metabolism. When lots of ketones show up in your urine, you can be pretty sure you’re burning fat, because that’s where ketones come from. Ketones are a wonderful metabolic fuel for the heart, the brain, and the muscles. Your body makes ketones all the time; it just doesn’t make that many of them, since it has plenty of glucose (sugar) around to use for primary fuel.

And that is the real purpose of the ketogenic diet in a nutshell: to get you to burn fat, rather than sugar.

Here’s how it works. When you go on a very low carb diet—restricting carbs to 20–50 grams a day—your body’s supply of constant glucose (from carbs) is suddenly cut off. Since there’s less sugar in the bloodstream to fuel your muscles, your body turns up the ketone-production machinery, burning more fat and making more ketones. When the ketones in your blood, urine, or breath rise to a certain level, you’re said to be in nutritional ketosis. A diet that generates that amount of ketones is known as a ketogenic diet.

Is keto a fad diet?

The keto diet isn’t all that new—it’s been around since the beginning of humanity. Dr. David Perlmutter, the integrative neurologist, says that ketosis is the original—and most optimal—state of metabolism. It’s almost certain that our hunter-gather ancestors spent most of their time in ketosis, since carbs (as we know them) just weren’t on the caveman menu. Cavemen would have had to become efficient fat-burners just to survive.

Even keto diet books aren’t new. The first commercial keto diet, called “Letter on Corpulence,” was published in 1863 by an obese English undertaker named William Banting, who lost 52 pounds in about seven months eating mostly meat and fat. And, of course, Dr. Robert Atkins introduced ketosis to America as part of his original Atkins Diet in 1972. Atkins found that nutritional ketosis forced his most stubbornly obese patients to start burning fat. In the absence of carbohydrate, their bodies had no other choice. So for many people—though certainly not all—the results of being in nutritional ketosis can feel a little like a miracle.

High-fat, low-carb diets were the standard recommended medical treatment for obesity (and diabetes) in the first half of the 20th century, but they fell out of favor beginning around the 1950s and 1960s. Dietary fat suffered a reversal of fortune in the public eye and was gradually demonized. It, along with cholesterol, was blamed for heart disease and tied to obesity. Health organizations began recommending low-fat (high-carb) diets, a move that ultimately led to the Dietary Guidelines and the antifat recommendations we’ve been living with for the better part of 40 years. And we all know how that’s worked out.

How to burn fat

One of the main reasons the ketogenic diet is so popular today is that it literally causes your body to switch from sugar-burning to fat-burning. Which is great, when you think about it.

Your body only can store about 1,800 calories of glycogen, the storage form of carbs. But you can store about 80 gazillion calories of fat. So if you could access that fat, and make it your main source of fuel, you would have an inexhaustible supply of energy, you’d be burning fat (and losing body fat), you’d be depriving cancer cells of their favorite food (sugar), and—theoretically, according to many experts and a fair amount of research—both your heart and your brain would work better. As the legendary ultra-marathoner and exercise physiologist Stu Mittleman once told me, “If you want to burn fat, you’ve got to eat fat.” Our metabolic goal is to become a better butter burner.

This changeover from a glucose-based fuel system to a fat-based fuel system is like changing from low-octane gas to diesel. It even has a name, thanks to Dr. Frederick Schwatka, a U.S. army lieutenant and medical doctor. Schwatka and his team went on an Arctic expedition and began eating the native Inuit diet—very high in fat, very low in carbs, essentially keto. They noticed that once they became what’s now being called “keto-adapted,” they had boundless energy.

The health benefits of keto diet

In recent decades, we’ve seen increases in the incidence of diabetes, obesity, heart disease and Alzheimer’s. Insulin resistance is a component or a factor in every one of these conditions. And when insulin resistance is a factor—as it so frequently is in metabolic diseases—ketogenic diets can be beneficial.

Since ketogenic diets are high in fat (and moderate in protein), they don’t jack up blood sugar. When blood sugar isn’t elevated, the demand for insulin is significantly reduced. When insulin is reduced, it isn’t constantly bombarding the cells asking them to take in more sugar. Now the cells start to relax, and become more insulin-sensitive (as opposed to resistant). Emerging research suggests that keto diets can reverse insulin resistance, and this may well turn out to be one of the ketogenic diet’s greatest contributions to health.

The keto diet is known to be effective for childhood epilepsy and is an accepted treatment at hospitals across the country like Johns Hopkins. The Navy—in conjunction with researchers at the University of Tampa—are experimenting with keto diets for Navy Seals.

And let’s not forget weight loss. As Atkins discovered, folks with the most stubborn cases of weight loss would lose weight when they were in ketosis.

What you should know about keto diet before trying it:

If you want to try going keto, here are a couple of things to know:

  • It doesn’t work for everyone. Some people just can’t get into ketosis. Don’t worry if you turn out to be one of them. You can still get a whole lot of benefits just eating low carb!
  • Don’t go “keto” at McDonald’s. A keto diet is not a reason to consume junk foods. Use high-quality fats such as coconut oil, Malaysian palm oil, grass-fed butter, ghee, MCT oil, or avocado oil, and high-quality protein like 100 percent grass-fed beef and wild salmon.
  • A keto diet is not a high-protein diet. Dietary protein is made up of amino acids, and some of those amino acids can convert to sugar in the body, so too much protein can knock you out of ketosis. Though there’s some debate in the keto community about this, most people recommend high-fat/moderate protein rather than high-protein/moderate fat.
  • Consider “flirting with ketosis.” Don’t get too obsessive about being “in ketosis.” Just aiming for ketosis—by eating a high-fat/moderate protein/very low-carb diet—will get you a lot of benefits.
  • What I just said doesn’t apply to everyone. There are some very weight-loss-resistant people who will just not drop weight (body fat) unless they’re in deep ketosis. So maybe the lesson here is that everyone’s different—don’t get locked into anything too rigid. Just experiment to see what works for you.

Taking supplements while on the keto diet

Take a high-quality multi to fill any micronutrient gaps.

High-fat diets can be low in fiber so I recommend a daily fiber supplement, which will also help keep your microbiome happy. I also recommend 2-4 grams of EPA-DHA, the two omega-3s you get in fish oil. Most people don’t get enough magnesium, and many people eliminate a lot of good magnesium-heavy foods when they’re cutting back on carbs, so I recommend a daily dose of magnesium. Then there’s vitamin D—in the 2,000 IU to 5,000 IU range, depending on your levels, which are easily tested. (Almost any reputable brand will do, as long as it’s in the vitamin D-3 form—cholecalciferol).

I think everyone on a keto diet—or really, any eating plan—should still take a multi. A high-quality multiple with clinically meaningful doses of nutrients in the correct forms is going to plug all the holes in your micronutrient intake.

Take a high-quality multi to fill any micronutrient gaps

While all ketogenic diets have the same purpose—to get you into nutritional ketosis—there are multiple approaches to getting there. Look around and see what fits you best. There are keto programs especially tailored to women, performance athletes, resistant weight loss. There are even programs that incorporate a technique called “carb cycling,” where you interrupt periods of keto dieting with a “carb feast.”

No diet is perfect for everyone or every situation. But the keto diet is a powerful tool that can achieve a lot of things when it’s done correctly.