Let's Talk About the Keto Diet

We’ve got the expert-approved scoop on this buzzy food plan, and a jillion facts and tips on whether it’s safe for you to try.

by Tula Karras Health Writer

It’s trendy and cool, and it’s being touted by everyone from professional athletes to Hollywood A-listers. Naturally, you’re curious, too. But what exactly is involved in the keto diet—and is it safe for everyone? What if you’re also dealing with a chronic condition? (What if you hate diets?) Like many new and buzzy things, the info out there on keto is sometimes confusing and often contradictory. We went to the experts to learn more about the science behind how keto works, and what the pros and cons are to trying it IRL. Check it out.

Keto Diet Basics

Our Pro Panel

We went to some of the nation’s top experts in the keto diet to bring you the most up-to-date information possible.

Fatima Cody Stanford, M.D., M.P.H.

Fatima Cody Stanford, M.D., M.P.H.

Obesity Medicine Physician Scientist

Massachusetts General Hospital; Harvard Medical School

Boston, MA

William S. Yancy, Jr., M.D.

William S. Yancy, Jr., M.D.

Director; Associate Professor of Medicine

Duke University Diet and Fitness Center; Duke University School of Medicine

Durham, NC

Lisa Sasson, R.D.

Lisa Sasson, R.D.

Associate Dean for Global Affairs and Experiential Learning; Clinical Professor of Nutrition and Food Studies

New York University

New York, NY

Keto Diet
Frequently Asked Questions
Will I lose weight on the keto diet?

Probably, but it could come back if you stop doing keto (which is true of any diet, really). Diets don't require people to confront one of the main reasons they’re overweight in the first place: emotional eating. Learning to not reach for the cookies or chips when you’re stressed is tough, but once you flex those muscles, you have more freedom and control.

Can the keto diet help my diabetes?

Yes! Keto is a low-carb plan, which can help you lower your blood sugar levels. One study found that after six months on a keto diet, people were able to significantly cut back on their insulin medication. And any diet that helps you lose pounds is also good for diabetes, since being overweight is a major factor in the disease.

Should I try keto if I have cancer?

There isn’t enough research to know one way or the other. Some research shows that cancerous tumors feed on glucose, which could give keto an advantage over higher-carb plans; but for other cancers—namely breast cancer, prostate and colorectal cancer—high-saturated-fat diets may increase the risk. In addition, dietary elements of any new eating plan can interfere with or augment certain drug treatments. Always consult your doctor before you begin any “eat to beat” cancer regimen.

What is dirty keto?

This is basically the first phase of the Atkins plan, with any and all fat-laden fare on the menu—greasy ribs, steaks sautéed in butter, three-egg omelets topped with a mountain of cheese—without any attention paid to healthier fat sources or vegetables. Experts do not recommend this version of keto, obviously. Not only is it the antithesis of a well-balanced diet, but it’s way too easy to overdo it on calories, which defeats the whole purpose of a diet.

What Does a Keto Diet Mean?

All diets have some sort of premise, and in the case of the keto diet, the premise is that if you can teach your body to use fats, instead of sugars, for energy, it will help you lose more weight faster.

So what is keto? That’s short for “ketogenic,” which describes a very-low-carb/high-fat diet that shifts a person’s body into a state of “ketosis,” or ketone-burning. (Ketones are chemicals produced by your liver after breaking down fat that may help suppress appetite.) Sounds a little sci-fi, but ketosis is really just an alternate way that your body burns the food you eat for energy.

Quick science lesson:

  • Your body has three options for fuel: carbohydrates, fat, and (in certain cases) protein.

  • Your body’s preferred form of gas for the engine is carbohydrates (think grains, fruits, and vegetables), because it is easily processed into glucose, which provides muscles and organs with energy.

  • However, if you cut your carb intake to a very low level, your body is forced to look to fat for fuel.

  • Your liver converts fat into ketones, which your body uses as energy.

The theory—which is still being debated—is that your body has to work a little harder to burn ketones than it does glucose, thus boosting your metabolism a bit and resulting in more weight lost.

Get All the Details on Ketosis

How Did the Keto Diet Start?

Even though the keto diet has 21st-century-internet-trend written all over it, it debuted in the 1920s, when doctors discovered that children with epilepsy had a sharp drop in seizures after their carbohydrates were restricted. (Scientists still aren’t sure exactly why it works.) With the introduction of anti-epileptic drugs, the diet fell out of favor, although some doctors still use it for kids with drug-resistant epilepsy.

In the 1990s, Robert Atkins, M.D., a cardiologist who had been exploring the idea of a low-carb diet since the ’70s, published a new diet book whose plan started people on a ketogenic phase in the first two weeks. The keto-style program went mainstream over the next decade and enjoyed a good run, but lost steam and support, in part because the plan gave a green light to foods that can increase heart disease risk (see: butter, steak, and bacon).

But the diet has made a comeback over the last several years. Thanks to celebrity weight-loss endorsements, niche products, and a slew of keto diet tomes and cookbooks, it’s all the rage again. What may give it staying power this time? An increasing number of doctors and registered dietitians have been recommending low-carb and very-low-carb diets to people with type 2 diabetes to help manage glucose and insulin levels, giving the keto plan a greater medical stamp-of-approval.

How Does the Keto Diet Work?

Despite all the hype around it, most people—even those on the keto diet—would be hard-pressed to explain the exact mechanism by which it triggers weight loss. Let’s start with the basics.

When you keep your carbohydrate intake in the keto-required 20 to 50 grams per-day range, which isn’t much (one apple has about 15 grams of carbs)—and replace those missing carbs with a high amount of fat (70% to 80% of calories)—the body kicks into ketosis, a.k.a. fat-burning, after several days. The amount of protein on the keto plan is also kept moderately low because it, too, can be converted into glucose by your body, making it a preferred fuel choice and preventing your body from staying in ketosis. (Protein also increases insulin secretion, which inhibits ketosis.) Unlike many other diets, which have wiggle room in how you divide your carbs/protein/fat content (perhaps focusing more on calories or portion sizes or quality of carbs), the finely-tuned ratios of the keto diet mean that any carb “cheating”—a cookie here, a bowl of rice there—will knock you out of ketosis, thus undermining the chemical reaction that’s at the heart of the diet.

So why do people lose pounds on the keto diet? It depends on whom you ask. Some experts maintain that when you are in ketosis, your body’s metabolism speeds up because it takes more energy to burn fat than carbohydrates. In fact, some research has found that people expend about 200 more calories a day on a low-carb diet (20% carbs) compared to a high-carb diet (60% carbs) when followed for about five months. However, other research shows that there is a negligible amount of extra calorie burn on the keto diet compared to a high-carb plan—around 50 calories a day.

Some experts believe that most of the weight shed on keto over time is due to things like the satiating aspect of all that juicy fat, which fills you up and leads to eating fewer calories overall. Other researchers point to the fact that the diet lowers blood sugar (glucose), which helps control your appetite, and may lower insulin levels, which tell your body to hold onto fat rather than burn it. What everyone does agree on is that if followed exactly, the diet can work in the short-term, though not necessarily any better than other low-calorie plans do.

What Are the Risks of the Keto Diet?

Every person’s body will react differently to the keto diet—or any diet for that matter—so doctors and nutritionists caution that what might be helpful for one person can pose a risk to another. Bottom line: No one should start living the keto life without first checking with their doctor. That said, it’s generally considered safe in the short-term, with a few caveats:

Potential risks of the kero diet include lack of nutritional balance, dangerous for the undiagnosed, could raise LDL cholesterol, stress on kidneys, temporary weight loss, and uncomfortable side effects
Nikki Cagle

Long-Term Safety Is Unknown

The biggest concern among the medical community is that there are no solid studies showing effects of the keto diet beyond two years. How come? Well, it’s tricky to study diets and dietary patterns—scientists would have to control literally every morsel a person eats and then tease out the effects of those foods from other lifestyle factors, like exercise.

We know more about other types diets, like high-carb or the Mediterranean diet, because those eating patterns occur naturally in a number of populations around the world. That said, some observational studies have found that the rate of death from cancer and heart disease is higher for people who claim to be on low-carb diets compared to those who say they are following high-carb diets.

It's Nutritionally Unbalanced

The diet requires that you severely slash some of the very foods that nutritionists urge us to eat more of, namely fiber-rich whole grains and high-fiber fruits like apples and bananas. In addition, because the carb limit on keto is so low, legumes and even some starchy veggies—carrots, potatoes, peas, and corn—are discouraged.

As a result, you could be missing out on cancer-fighting and heart-healthy nutrients and phytochemicals—especially if you're not being mindful of the healthiest keto-friendly options. You may also be hit with side effects like constipation because of lack of fiber. In fact, when children with epilepsy are put on the diet, they are required to take supplements, often including magnesium, potassium, selenium, sodium, and zinc, to keep nutritional requirements in balance.

The bright side of carb-cutting: Many carbs that make up the standard American diet are nutrient-poor processed foods like chips, crackers, and white bread—foods that are linked to a higher risk of diabetes. Some docs maintain that for certain individuals, the health-related weight loss benefits of keto (namely a drop in total cholesterol, triglycerides, and blood pressure as well as better control of insulin for people with type 2 diabetes) overrides the nutritional challenges of the diet.

Ketosis Can Be Dangerous for Undiagnosed Diabetes

Cutting almost all carbs from your diet can cause glucose—a.k.a. blood sugar—levels to plummet, along with insulin (the hormone made by the pancreas that helps ferry glucose from your blood into cells). For a person without diabetes this doesn’t pose a danger. And for someone with diagnosed diabetes who is monitoring blood sugar levels and using the keto diet along with medical supervision to reduce the need for insulin medication, it may even be desired. But for someone who has no idea they have diabetes or pre-diabetes, a sudden and sustained drop in blood sugar—brought on by the keto diet—might, in rare cases, cause them to pass out or (in very rare instances) die.

It Might Raise Your LDL Cholesterol

People with high cholesterol—and with high low-density lipoprotein (LDL) levels in particular—should have their cholesterol monitored, since some studies point to an increase in LDL or “bad” cholesterol when on a keto-style diet, putting you at greater risk for heart disease. However (drum roll), not all LDL particles are created equally, and research suggests that the type of LDL particles that increase on the keto diet are not the most dangerous ones (a.k.a. the small, dense particles that stick to your artery walls). Nevertheless, if cholesterol is a concern, talk with your doc.

It Could Raise Your Odds of Kidney or Liver Trouble

People with a risk of kidney stones or a family history of kidney disease should be cautious and check with their doctor before getting on keto. Studies of children with epilepsy who followed the keto diet for several years found that a small percentage developed kidney stones, possibly because the uric acid that builds up from protein metabolism can lead to stones (reducing your reliance on animal protein in favor of vegetable protein may help).

However, for those with healthy kidneys and no history of kidney stones, the diet is likely fine; the amount of protein in the keto diet is not much higher than the average American diet, say experts, and what harms the kidneys more than excess protein is high blood sugar and high blood pressure, both of which can be improved by the keto diet and weight loss overall.

As for the liver, the science is still young, and experts are divided. Some practitioners maintain that the risk to the liver is no higher on keto, and there is even research showing that people with nonalcoholic fatty liver disease improve on the diet. Other medical experts caution that each person is unique and have documented cases where a keto diet resulted in fatty liver disease.

It’s Restrictive

The keto plan is a diet in the extreme sense—not only does it prescribe what you can and cannot eat, it restricts an entire food group. As a result, it can be hard to stick with, especially over any significant period of time. And the moment you re-introduce carbs into your meals (a bagel at breakfast, pasta at dinner), the weight can come back, particularly water weight, since carbs cause you to retain water. Also, a restrictive diet can play head games with eaters who tend toward disordered eating, thrusting them into a mindset where they become fixated on what goes in their mouth and watch the scale like it’s a Twitter feed.

That said, there are those for whom a keto diet can actually feel easier, since it's straightforward on what the rules are and may lessen feelings of hunger.

It Has Side Effects

Any big change in a person’s diet can result in physical symptoms, and the keto diet is no exception. In fact, it’s practically a given with this diet because of the learning curve your body has in order to shift from carb-burning to fat-burning.

Symptoms include:

  • fatigue

  • foggy thinking

  • headaches

  • nausea

  • diarrhea

These symptoms are common in the first week—thanks in part to the loss of water and electrolytes that extreme carb-cutting results in. All these together have been termed the “keto flu.” In addition, the lack of fiber can lead to constipation for some. Symptoms usually subside after the first week or two (and may be avoided entirely with adequate hydration and electrolyte intake).

Learn More About the Keto Flu

It’s Costly and Leaves a Big Carbon Footprint

Your focus may be on weight loss, but the keto diet can shed dollars from your wallet, too. Most keto dieters get their fat from pricey sources like dairy and meat, which also contribute to the top causes of climate change (methane from cows and industrial-plant pollutants which process all that meat and dairy). For people who are passionate about environmental issues, keto is not exactly the poster child for an earth-friendly meal plan.

Who Should Consider the Keto Diet?

There is good research showing that if you have certain chronic health conditions, the keto diet can help. If you check any of these categories, consult your doctor to see if jumping aboard the keto train might be a good option for you:

Type 2 Diabetes

The strongest evidence for going keto is for those with type 2 diabetes—a.k.a. people who don’t produce enough insulin or are insulin-resistant. Some research finds that after six months on a keto diet, blood sugar levels in type 2 diabetics can normalize to the point that they can reduce or curtail insulin and other blood glucose-lowering medications.

How so? Keto’s low carb count means you naturally have less glucose coursing through your blood, and therefore you don’t have as great a need for insulin to move glucose into the cells. Another big fat bonus: The weight loss alone from a keto plan can lower a person’s reliance on blood glucose-lowering medications (being overweight can impair your body’s ability to make and use insulin, and losing weight can improve insulin sensitivity and use), which is no small thing, since one of the side effects of injected insulin is (cruelly) weight gain.

Heart Disease

A high-fat diet to combat heart disease? It sounds crazy, but science is beginning to show that the keto diet (and other low-carb diets) can raise good cholesterol (HDL) and lowering triglycerides, a type of lipid tightly linked to arteriosclerosis (a.k.a. hardening of the arteries that can lead to a heart attack). Some people with high cholesterol who stick with the keto diet for several months see beneficial changes (such as reduced triglycerides—which can start going down within weeks—and increased good HDL) and are able to reduce the amount of statin medications they’re on or get off them altogether. Experts emphasize, however, that you shouldn’t go hog- (or butter-) wild with saturated fats—found mostly in animal products—which are linked to increase in LDL and a lowering of HDL.


Anyone who is overweight (often indicated by a BMI over 25) should be altering their eating habits in order to shed weight and lower their risk of weight-related chronic diseases. For those who have tried—and failed—on low-fat plans, the keto diet might be a winner. Most people lose weight on keto, especially at the beginning (albeit partly due to water-weight loss). That initial speedy loss can be motivating and spur dieters to keep going. (Note: Not all doctors believe that people with obesity should experiment with such an extreme diet; a more moderate approach may be more sustainable over a lifetime.)

Metabolic Syndrome

A cluster of conditions that occur together, metabolic syndrome is marked by high blood pressure, high triglycerides, low HDL (good) cholesterol, high blood sugar and excess body fat around the waist. Like a perfect storm, each of the conditions biochemically influences the others and, together, they significantly raise a person’s risk for heart disease, stroke, and diabetes. Because of the keto diet’s benefits for people with these individual conditions, it can also help with metabolic syndrome.

Are There Different Versions of Keto?

The OG plan relies on a finely calibrated equation of carbs, fat, and protein in order to generate ketones. If you start messing with the math, it’s pretty easy to boot yourself out of ketosis.

But staying in ketosis isn’t necessarily the end-all be-all for the diet if you consider its other benefits: feeling fuller so you don’t snack your way through the pantry and weaning yourself off a high-carb feedback loop that has you craving sugar all the time. If you’re willing to play a little loose with the rules, you might find a keto-style plan that’s easier to commit to for the long term. Let’s look at a few ways to live la vida keto:

Standard Keto Diet (SKD)

This is the mothership, the version that doctors put diabetic or epileptic patients on to achieve full-blown, steady ketosis. Here’s how the diet breaks down:

  • 70% to 75% fat

  • 20% protein

  • 5% to 10% carbs (measured in grams, no more than 50 grams/day; some people may need to drop to 20 grams to achieve ketosis)

Experts recommend you bank your fat calories with at least some—and preferably a lot of—unsaturated and monounsaturated sources, such as fish, avocados, nuts, olive oil and MCT (medium-chain-triglyceride) oil, an oil found in coconuts and which some adherents take as a supplement (it creates more ketones than other types of fat and allows you to up your carb intake a bit without bumping you out of ketosis). People who are committee to SKD often use urine strips that detect ketones in your pee and turn a certain color when you are in ketosis. And you’ll know you’re in ketosis if your breath smells fruity or metallic.

Cyclical or Targeted Keto

For those who can’t handle a 24/7 keto existence—or if you desperately need a carb boost on days when you want to clock an intense aerobic exercise session (your body needs more glucose during aerobic exercise)—doing keto for, say, five days on, two days off, may work better with your lifestyle and schedule.

Modified Atkins Diet (MAD) or High-Protein Keto Diet (HPKD)

On these tweaked plans, you’re eating less fat and more protein, so it won’t necessarily keep you in ketosis. It can, however, keep your calorie intake down because protein is satiating (even more so than fat). The breakdown looks like this:

  • 60% to 65% fat

  • 25% to 30% protein

  • 10% carbohydrates

Modified Keto

This is the plan that many people default to when sticking with SKD becomes too difficult, too boring, or results in chronic health issues (like constipation). A more generous allotment of carbs means you don’t have to track every bite as religiously. And the lower-fat, slightly-higher-carb version allows for a few more options like fruits, legumes, and whole grains. And that’s OK if your goal is moderate weight loss. It won’t put you or keep you in ketosis, however. Your daily intake breaks down like this:

  • 55% fat

  • 30% protein

  • 15% carbohydrates

What’s It Like Living on the Keto Diet?

There’s no way around it—if you’re going to do the keto diet properly, you’re going to be giving up a lot of foods that are typically associated with comfort: warm breads, cookies, pumpkin pie. You might, say experts, find your tastebuds adapt, so you eventually stop craving sugar-laden fare. But living in such a restricted way can still make socializing awkward (and restaurant menu options limited). If your primary goal is weight loss, there are other less-restrictive options that may easier to integrate with your lifestyle and sustain over the long-term.

Then again, plenty of people have tried the keto diet and found success with it. If you’ve tried other methods of losing weight and failed, having a more regimented plan like keto could be what you need to stay on track and keep yourself accountable. It may require planning meals well in advance and making food at home as opposed to eating out. It could be a shock to your system—but in a good way that jumpstarts your commitment to healthier all-around living.

Think the Keto Diet May Be Right For You?
Tula Karras
Meet Our Writer
Tula Karras

Tula Karras is an award-winning journalist, editor, and content creator who specializes in health, nutrition, and profile writing. She has written for numerous print and online publications, including Self, Parents, Real Simple, National Geographic, Prevention, Cosmo, Consumer Reports, Health, Good Housekeeping and Yoga Journal. She has ghost-written two books and is based in Austin, Texas.