What Is a Ketogenic Diet?

Ketogenic diets are low in carbohydrates and high in fats, a combination that sends your body into a state of ketosis. . Ronda Kimbrow/Shutterstock

You've heard of low-carbohydrate, high-protein diets like the Atkins diet and paleo diet. A strict version of those diets has also gained popularity, simply called the ketogenic or keto diet.

These ketogenic diets are occasionally popular because they allow people to lose weight quickly, but do you know what, exactly, they do in your body to trigger weight loss?

In a standard carb-loaded American diet, the body burns glucose from carbohydrates as an energy source in a process called glycosis. But when you limit your carbs and increase your fat intake, your body moves into a metabolic state of "ketosis," meaning that it's burning fat stored in your body instead of glucose, according to WebMD. Ketosis also drastically reduces blood sugar and insulin resistance.

As Dr. Eric Westman, director of the Lifestyle Medicine Clinic at Duke University, told Time magazine, "You determine what your body burns for fuel based on what you feed it."

Possible medical benefits

Example of a plate of food in a Ketogenic diet with avocado, eggs, lettuce and bacon
Ketogenic diets have been used to treat pediatric epilepsy, multiple sclerosis and cancer. Elena Shashkina/Shutterstock

A ketogenic diet has been used for almost 100 years to treat pediatric epilepsy, Scientific American reports, because a ketogenic diet mimics fasting, which has long been known to have a therapeutic effect on seizures. Similar to a state of ketosis, the body also burns fat for energy during fasts. Usually, a pediatric ketogenic diet starts with 24 hours of fasting in a hospital setting, where doctors can monitor frequency of seizures, medication, and help educate the parents on the ins and outs of the diet.

Because of these neuroprotective benefits, researchers have questioned whether a ketogenic diet may also be beneficial for other brain disorders such as Parkinson’s, Alzheimer’s, multiple sclerosis, sleep disorders, autism and brain cancer, reports Harvard Health. So far, there are no human studies that support recommending ketogenic diets as part of treatment for those conditions.

A recent study published in Science Immunology suggests that the keto diet can protect mice from influenza infections. However, experts who reviewed the research cautioned that although the results are interesting, they may not easily transfer to humans.

Types of ketogenic diets

Not all ketogenic diets are the same. They all encourage followers to limit carbohydrates, including breads, sweets, sugary drinks, legumes, fruits and potatoes. Instead, the diets are rich in meats, eggs, cheese, fish, nuts, butter, oils, seeds and fibrous vegetables.

The Atkins diet gradually increases carbs over time, going from 20-25 net carbs per day to 80-100 net carbs per day in four phases. The keto diet, however, puts strict limits on both carbs and protein.

As The New York Times points out, there have been many studies of the keto diet over the years, but most have been short and limited in scope.

"Some doctors and health experts say it can lead to quick weight loss but that it is no more effective than other diets in the long term. And many say they find it worrisome because it encourages foods high in saturated fat, which have been linked to heart disease, while restricting nutrient-rich foods supported by decades of research, like beans, fruits, starchy vegetables and whole grains," NYT health report Anahad O’Connor writes.

In addition, a recent essay published by several doctors in JAMA Internal Medicine questioned using the diet as a treatment for obesity and diabetes. They referenced research that suggests the keto diet was no better than low-fat diets in controlling blood sugar for diabetes. The diet could prompt other concerns, including an increase in cholesterol, as well as constipation and fatigue.

Keto vs. keto 2.0

Recently, a more flexible version of the keto diet has surfaced.

"In a traditional keto diet, 75-90% of the calories come from fat, about 5% from carbs, and the remaining percent from protein," explains registered dietician Cynthia Sass, MPH, RD, in Health. "In keto 2.0, the proposed macros shift to 50% fat, 20% carb, and 30% protein."

Although those percentages are still limiting, Sass points out that the modifications, make room for more plant-based foods and emphasizes leaner protein sources.

Ethan Weiss, M.D., a San Francisco–based cardiologist, tells Mind Body Green that substituting mostly plant-based sources for those high in animal-based saturated fats preserves the integrity of the diet but protects heart health. It also makes the diet more accessible and helpful to more people.

“It can be easier to get into and maintain ketosis when prioritizing foods rich in unsaturated fats,” he says. “It affords all the benefits of conventional keto, but fixes the biggest concerns.”

Starting a ketogenic diet

Ketogenic diet plate of chicken and salad with tomatoes and avocado for fat
A true ketogenic diet can be hard to maintain, so do it under the care of a doctor or nutritionist to make sure you're getting adequate nutrition. Elena Shashkina/Shutterstock

Following a ketogenic diet can be difficult, because in order to start it, you have to go off carbohydrates almost entirely.

So what exactly can you eat on a ketogenic diet? Some options are below:

  • Meat: Beef, goat, lamb, turkey, pork, veal, chicken.
  • Fish: Salmon, trout, catfish, sardines, tuna, haddock
  • Fruits: Strawberries, blueberries, raspberries, avocado
  • Vegetables: Broccoli, asparagus, Brussels sprouts, cucumbers, peppers
  • Nuts and seeds: Almonds, walnuts, sunflower, pumpkin, sesame, etc.
  • Dairy products: Cheese, Greek yogurt, sour cream, heavy cream.
  • Fats and oils: Peanut butter, flaxseed oil, butter, sesame oil, olive oil and almond oil

"Instead of engaging in the next popular diet that would last only a few weeks to months (for most people that includes a ketogenic diet), try to embrace change that is sustainable over the long term," writes Marcelo Campos, M.D. for Harvard Health. "A balanced, unprocessed diet, rich in very colorful fruits and vegetables, lean meats, fish, whole grains, nuts, seeds, olive oil, and lots of water seems to have the best evidence for a long, healthier, vibrant life.