What Scientists Say About the Keto Diet

If you've ever dabbled in the world of dieting, you're likely to have come across the keto diet.

As many as 7 percent of Americans followed this eating plan in 2022, according to data from the International Food Information Council, while the global ketogenic diet food market skyrocketed to $8.8 billion that same year.

The keto diet is a low-carb, high-fat diet with moderate levels of protein. And while this restrictive eating pattern can yield impressive results in the short-term, is it really "good for you?"

Newsweek spoke to the experts to find out.

"The goal [of the keto diet] is an extreme restriction on carbohydrate to the extent that the body shifts from burning a combination of glucose and fat for fuel, to only burning fat for fuel—a condition referred to as ketosis," Christopher Gardner, Rehnborg Farquhar professor of medicine and director of nutrition studies at the Stanford Prevention Research Center at Stanford University, told Newsweek.

But what does this "extreme" restriction look like in practice? "The amount of carbohydrate needs to be around 5 percent of calories," Gardner said. "Typical diets in the U.S. are around 50 percent calories from carbohydrate, so this is DRASTIC."

A common misconception is that these carbs are then replaced by high protein foods and meat. "Many people misunderstand the diet and assume it is high protein, and high meat," Gardner said. "[But] the body doesn't have any place to store protein consumed in excess. [So] once daily needs have been met, the extra protein is converted to.....carbohydrates, the very thing needed to be avoided to be in ketosis.

"In order to be in ketosis, the emphasis needs to be on fat. A 'Well Formulated Ketogenic Diet' is around 75 percent fat. The typical American diet is around 35 percent fat, so this means more than a doubling of fat intake."

So what can you actually eat as part of a keto diet plan?

"Foods promoted to eat are butter, lard, poultry fat, plant fats (olive, palm, coconut oil), avocado, coconut, certain nuts (macadamia, walnuts, almonds, pecans), and seeds (sunflower, pumpkin, sesame, hemp, flax), non-starchy vegetables (leafy greens and kale, cauliflower/broccoli, onions, cucumber, lettuces), berries in small portions, 90 percent or higher dark chocolate, plain coffee and tea," Nancy Oliveira, dietitian and manager of the nutrition and wellness service at Harvard Medical School's Brigham and Women's Hospital, told Newsweek.

"Protein stays moderate from beef, poultry, fish, pork, bacon, organ meats, eggs, tofu, certain nuts and seeds.

"[You're] not allowed [to eat] bread, pasta, rice, any grains, flour, most fruits, potatoes, winter squashes, corn, peas, beans, regular milk and milk products."

Sticking to this strict diet plan can clearly takes a lot of willpower, but is it worth it?

"The ketogenic diet has been shown to produce favorable weight loss results in the short term period," Kristen Smith, nutritionist and national spokesperson for the Academy of Nutrition and Dietetics, told Newsweek.

"In addition to weight loss, the ketogenic diet has also shown positive short-term changes in insulin sensitivity, increased ['good'] cholesterol and decreased triglycerides [the most common type of body fat.]"

There are, therefore, some people who might benefit from keto. "For people with pre-diabetes or diabetes, the ketogenic diet can be very helpful in lowering blood glucose and blood insulin levels," Gardner said.

The keto diet is also often used as a treatment for those with epilepsy and was actually initially created back in the 1920s as a treatment to help children with epilepsy suppress seizures.

But is this diet for everyone?

"For most people who try this diet, the success is short-term," Gardner said. "It is so restrictive that most people can't maintain it long-term. A 2019 meta-analysis looked at 6- and 12-month effects of the diet. There were several benefits at 6 months, but these were gone at 12 months. One reason for a lack of persistence of benefit is the inability to stick with the diet."

Not only is it hard to stick to, but the keto diet can also be detrimental to our overall health.

"I do not recommend this diet," Gardner said. "It is a high saturated fat and low-fiber diet. It consistently raises ['bad'] cholesterol. I study the microbiome, and in our studies we see benefits of dietary fiber for a healthy microbiome."

Studies have shown that a healthy microbiome—i.e. the trillions of bacteria and microbes that call our guts home—may play an important role in protecting our bodies against a range of different health conditions, including cardiovascular disease, obesity, depression, and cognitive disorders like Alzheimer's disease and Parkinson's. Therefore, keeping it well fed is essential for our overall well-being.

As well as starving your gut microbiome, not eating enough fiber can cause other uncomfortable side effects. "Constipation is a common complaint for individuals following the ketogenic diet, especially during the initial phase of the diet," Smith said.

And this isn't the only waste pipe that can be affected. "Potential negative side effects of a longer-term ketogenic diet could be an increased risk of kidney stones (this has been seen in people following keto long-term as an epilepsy treatment) and increased blood levels of uric acid which is a risk factor for gout (as a gout-protective diet includes fruits, vegetables, whole grains, and low-fat dairy)," Oliveira said.

As well as being low in fiber, the restrictive nature of the keto diet makes it very difficult to get appropriate levels of key vitamins and minerals. "I wouldn't recommend a person start out with a keto diet for weight loss or even diabetes control, because I don't think you can create a balanced diet from it," Oliveira said. "Sure, you can take a multivitamin, but they don't have fiber so you aren't feeding your gut microbiome. You also miss out on the hundreds of health-promoting plant chemicals in a whole food."

There are also certain individuals who should definitely avoid this diet. "The ketogenic diet is not suitable for all individuals due to its severe restriction of a major macronutrient and challenge with compliance," Smith said. "Some groups that should not follow the keto diet are pregnant women, individuals with a history of disordered eating or individuals at high risk for heart disease."

So how should we be eating instead? "The emphasis in my opinion is to eliminate as much of the simple sugars (i.e., added sugars and refined grains—the hallmark of junk foods) as possible," Gardner said. "According to national data, around 40 percent of the calories in the U.S. diet come from these low-quality carbohydrates. I think half of that should be replaced with foods high in unsaturated fat, and half of that should be replaced with foods that are high in fiber.

"The Mediterranean diet is full of flavor, not restrictive, and allows for more people to follow this pattern for longer periods of time, even a lifetime."