Reviewed by Michael W. Smith, MD on July 11, 2018
From the WebMD Archives

July 9, 2018 -- As a 41-year-old trucker who delivers crude oil cross-country, Jose Sandoval was hardly the type to keep up on the latest celebrity diets.

But when a co-worker mentioned he’d slimmed down by “going keto,” Sandoval -- a father of four who was pushing 300 pounds -- perked up.

He’d already followed doctor’s orders to limit fat and eat more vegetables and grains, but his weight was stagnating, and his diabetes was getting worse. So in January, after reading a stack of books about the ultra-high-fat, ultra-low-carb diet, Sandoval traded his morning cereal for butter-infused coffee, gave up his homemade tortillas and starchy vegetables, and began piling on the avocados, bacon, and oils.

“I don’t get hungry. I have more mental clarity. And I have so much energy,” says Sandoval, now a buff 230 and off his diabetes medication.

Nearly a century after Mayo Clinic doctors came up with it as a last-ditch therapy for epileptic children, the ketogenic diet is back and hitting the mainstream, lauded as everything from a quick way to drop pounds to a promising therapy for neurological problems.

Statistics showing just how many people are on the diet are hard to find. But Google searches for “ketogenic” have increased nearly eightfold in 5 years, inspired by endorsements from celebrities like Halle Berry and Vanessa Hudgens. Netflix even rolled out a new film, The Magic Pill, which covers people using the diet for everything from treating autism to fighting cancer.

Not surprisingly, the diet has also drawn criticism, with some calling claims about its far-reaching health benefits “patently ridiculous” and potentially harmful.

Even advocates caution that the diet, while effective for certain problems, is not for everyone, and it’s not easy.

Keto 101

While everyone and their neighbor seem to report they’ve tried the ketogenic diet, they probably haven’t, says Kristen Mancinelli, a registered dietitian and author of The Ketogenic Diet. “People think that if they cut out some carbs and add a little fat to their plate, they are doing it,” she says. “They’re not. This diet is extremely strict.”

You can put your body into a ketogenic state without following the diet to the letter. Generally, it means eating very few carbs, lots of fat, and protein.  

Many people on the diet shoot for about 80% of their calories from fat, 5% to 10% from carbohydrates (the typical U.S. diet is about 55% carbs), and the rest from protein. That means keeping carbohydrate intake around 20 grams per day. An apple has more than that.

There are two purported benefits of dipping so low in carbohydrates: Within a week, blood sugar stabilizes and insulin levels dip, a bonus for anyone struggling with diabetes. Without carbohydrates (the body’s typical go-to fuel), the body slips into “nutritional ketosis,” in which the liver breaks down fat for energy. In the process, it produces compounds called ketone bodies that enter the spinal cord and brain, where they have several impacts, including dampening hunger.

“The irony of most diets is that you start with people who are overeating because of excessive hunger and then you cut back calories -- so their hunger goes up even more,” said David Ludwig, MD, a professor at Boston Children’s Hospital and Harvard Medical School.

He notes that while people on calorie-restrictive diets lose weight at first, they often gain it back as their hunger climbs, their metabolism slows, and their body begins to store more fat.

Early research suggests a ketogenic diet may be different.

One large analysis of 13 trials, published in the British Journal of Nutrition, suggested that people on the diet lose more weight and keep more off than people on lower-fat diets that allow for more carbs. In another 8-week trial including 34 obese men and women, those on a ketogenic diet lost nearly 10% of their body fat, while those on a low-fat diet lost 2.3%.

“In terms of the science, we have to stay tuned,” said Ludwig, who recently launched a $12 million, 3-year study of the diet. “But it may be that the brain perceives less deprivation and the metabolic rate speeds up, so you can lose weight with your body’s cooperation.”

Beyond Weight Loss

Weight loss aside, some clinics and people have begun to explore the ketogenic diet as a way of managing diabetes.

One recent study of 34 overweight adults with prediabetes or type 2 diabetes found that those on the diet had greater improvements in blood sugar and were more likely to come off their diabetes medication than those on a low-fat, low-calorie diet that maintained a typical amount of carbs.

“I would say it is by far the diet of choice for diabetes,” said Keith Runyan, MD, a retired kidney specialist who has managed his own type 1 diabetes for 6 years via the diet and wrote a book, The Ketogenic Diet for Type 1 Diabetes.

Eric Kossoff, MD, who is a world expert on the use of the ketogenic diet for seizure disorders, says the evidence is solid when it comes to children: About half who try it see half of their seizures go away, and some see them halt altogether. Now, adults are also using it to treat seizure disorders. And neurologists are beginning to explore other ways to use the diet.

“They have begun to say if it works for epilepsy, maybe it will work for other conditions affecting the brain,” said Kossoff, who is medical director of the Pediatric Ketogenic Diet Center at Johns Hopkins Hospital in Maryland.

Ketones, he says, impact mitochondria, the cellular powerhouses of neurons. Also, fats benefit the brain, and altered glucose metabolism can have anti-cancer effects.

It’s too early to recommend the diet for such uses, he says, but studies are underway exploring versions of it for Alzheimer’s disease, autism, traumatic brain injury, and brain cancer.

“It’s an intriguing and very exciting area of research,” he says.

Cons and Criticisms Abound

Not everyone is sold.

A recent U.S. News and World Report ranking of 40 diets placed the ketogenic diet dead last, because of concerns about the high level of fat, which could potentially worsen cardiovascular health, and the stress it can place on the liver. (People with liver disorders are advised not to do it.)

And that Netflix documentary, The Magic Pill, which was filmed in Australia, has prompted outrage from the Australian Medical Association. The group’s president, Michael Gannon, called the film’s claims “patently ridiculous” and, in an interview with The Daily Telegraph, he called it a contender “in the awards for the films least likely to contribute to public health.”

Meanwhile, the American Heart Association recently warned that coconut oil -- considered a mainstay of the ketogenic diet -- is loaded with saturated fat and can raise bad cholesterol. The AHA recommends eating no more than 6% of saturated fat as part of a healthy diet. It’s important to note, too, that eating coconut oil is not required to reach a ketogenic state.

Then there are the side effects.

As the body adapts to nutritional ketosis, many adherents get the “keto flu” -- complete with fuzzy-headedness, nausea, fatigue, and headaches. It can last 4 to 5 days. Because the diet can lack fiber, constipation can be a problem, and so can a lack of vitamins, minerals, and electrolytes, along with kidney stones. And because the diet is so restrictive, it can be hard to stick with long-term.

“If someone wants to go ketogenic, I make it quite clear that it is very hard to do. And I don’t recommend it for everyone,” says Mancinelli, the registered dietitian who wrote a book about the keto diet. Instead, she often recommends a more manageable low-carb diet, along with intermittent fasting, which can prompt some of the same results for the body.

But, she says, for people who like an all-or-nothing approach, the rigor of keto can be a perfect fit, and the fast weight loss at the beginning can be motivating.

Mancinelli says clients should avoid going overboard on saturated fats like coconut oil and strive to get a mix of fats and low-carb vegetables. There are typically no calorie restrictions on the diet, because usually, fat makes people feel fuller and their appetite naturally diminishes. (Often, people aren’t hungry for three meals a day anymore).

“That said, being on keto is not a license to overeat,” she advises.

Sandoval, who read Mancinelli’s book three times, listened. Today, he has no doubt he’ll reach his goal weight of 190 pounds.

“People have a lot of misperceptions about it, thinking you have to just eat bacon and eggs, and that it’s not sustainable,” he says. “All I know is, it’s working for me.”

Show Sources

Kossoff and Hartman, Current Opinions in Neurology Review, 2012.

Eric Kossoff, MD, medical director, Pediatric Ketogenic Diet Center, Johns Hopkins Hospital, Maryland.

Kristen Mancinelli, registered dietitian; author, “The Ketogenic Diet: The Scientifically Proven Approach to Fast, Healthy Weight Loss.”

David Ludwig, MD, PhD, professor of pediatrics and nutrition, Harvard Medical School and Harvard T.H. Chan School of Public Health.

Bueno et al. British Journal of Nutrition. October 2013.

Abbasi, JAMA, January 2018

Saslow et al, Nutrition and Diabetes, 2017.

U.S. News and World Report.

Sacks et al., Circulation, June 2017.

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