What Is the Ketogenic Diet?

Ketogenic diet

Verywell / Debbie Burkhoff

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A ketogenic diet—also called a keto diet—is a very low carbohydrate diet designed to force your body to burn fat instead of glucose for energy. Proponents of the diet claim that it is the most effective way to burn fat and achieve or maintain a lean body. The diet is also used in medical settings.

But nutrition experts worry that this diet is too strict to be sustainable for many people. Learn more about the advantages and disadvantages of a keto diet before you decide if it is right for you. Before starting this type of eating plan, check with your healthcare providers, especially if you have an underlying health condition.

What Experts Say

"The ketogenic diet severely limits carbohydrate to force the body to burn fat. However, carbohydrates are limited so much on this diet that veggies and fruit are restricted, which experts agree limits fiber and nutrients. Plus, restriction often promotes long-term weight gain."

Willow Jarosh, MS, RD


The ketogenic diet has been in use in medical settings for about 100 years. According to medical researchers, the diet was developed in the 1920s to mimic fasting diets that were used as early as 500 B.C. to treat epilepsy and other seizure disorders. While it was used successfully to treat the disease for many years, interest in the diet diminished in the 1990s when anti-epileptic drugs (AEDs) were introduced.

However, the diet became popular again as certain forms of drug-resistant epilepsy and other pediatric epilepsy syndromes were identified. The ketogenic diet was used successfully in many of these patients.

In recent years, the keto diet's role in medicine has been expanded and the program is also sometimes used to treat other conditions including headache, neurotrauma, Alzheimer's, Parkinson's, amyotrophic lateral sclerosis (ALS), cancer, stroke, mitochondrial disorders, brain trauma, psychiatric disorders, autism, and migraines.

Researchers are conducting studies to learn why the diet has a positive effect on some of these conditions. But many published reports suggest the ketogenic diet helps to normalize atypical metabolisms which may cause the disorders.

The diet has also become popular in some athletic and weight loss communities. People learned that medical patients who are put on the diet often lose weight—which led to the diet's popularity as a quick weight-loss method.

Some celebrities and professional athletes have promoted the diet as their preferred eating plan for weight loss, weight maintenance, and improved athletic performance. The resulting media coverage has boosted the keto diet's popularity even further.

How It Works

A ketogenic diet is one in which carbohydrate intake is severely restricted. However, not all low-carbohydrate diets are ketogenic. There are three approaches to low-carb eating and only one of them is considered a true keto diet.

On a ketogenic diet, your body goes into a state of ketosis, where it burns fat as fuel. This process produces ketones, which gives these diets their "keto" name.

On most ketogenic diets, you consume 70–75% of your calories from fat. Of the remainder, you consume about 5–10% of your calories from carbohydrates and the rest from protein.

ketogenic diet calorie distribution
 Illustration by Emily Roberts, Verywell

There is some variation in the structure of the diet. Some sources say to consume no more than 20 grams of carbohydrates per day, while others cite up to 50 grams, and many recommend no more than 5% of calories from carbs.

Meals are most often built around fat sources such as fatty fish, meat, nuts, cheese, and oils. Some versions of the keto diet advise that you eat only certain types of fat. For example, many authors advise steering clear of oils that are high in polyunsaturated omega-6 fats (soy, corn, cottonseed, safflower) because they are considered to be less healthy.

Other versions of the diet recommend fats high in medium-chain triglycerides (MCT), such as coconut oil and MCT oil, as these fats are easily turned into ketones by the body.

In general, people on ketogenic diets tend to consume a lot of foods high in monounsaturated and saturated fats such as olive oil, butter (from grass-fed cows is recommended), avocado, and cheeses. The high oleic types of safflower and sunflower oils (but not the regular forms of these oils) are often recommended, as they are high in monounsaturated fats and low in polyunsaturated fats.

While there is no need to time meals, purchase specific products, or eat certain required snacks or beverages, the diet does not provide a lot of flexibility in terms of food choice because carbohydrates are so severely restricted.

Pros and Cons

Because there is a long history of use in the medical community, there is a wealth of research that explains and supports the mechanism of ketosis for the management of disease and (to a lesser extent) for weight loss. Those who use the diet to lose weight are likely to see results quickly because eliminating high-carbohydrate foods may reduce overall calorie intake and also reduces water weight.

However, while your body is adjusting to ketosis, there can be negative symptoms including fatigue, weakness, light-headedness, headaches, mild irritability. Additionally, this way of eating eliminates or severely restricts foods high in fiber and other nutrients, which can lead to health problems such as constipation and vitamin or mineral deficiencies.

Lastly, diets such as the ketogenic diet are often used only short-term because those without a medical condition may not be motivated enough to eliminate foods they love or are used to eating. Highly restrictive diets have a tendency to backfire and can cause weight gain as a result. Also, there is not enough evidence to support the efficacy of long-term use of ketogenic diets (greater than one year). Therefore, more scientific research is still needed to understand both the efficacy and safety of the diet for long-term use.

Common Myths and Questions

Because the ketogenic diet has many variations—many of which are promoted in celebrity circles, fashion magazines, and online by fitness bloggers—there is some confusion about the eating style.

Question: How will I know if my body is in ketosis?

Most people on a ketogenic diet test for the presence of ketone bodies. Ketone bodies—or ketones—are a byproduct of ketogensis, and your body excretes them in your urine. People commonly use urine sticks to see what their ketone levels are and if they are in ketosis. It can take several days or several weeks to get your body into ketosis.

Question: Will I always be tired if I go on a ketogenic diet?

No. Most people adjust eventually as their bodies learn to burn fat as fuel. However, you should expect some fatigue during (at least) the first week of the program.

Myth: Ketogenic diets are extremely dangerous and can even cause death.

Some people confuse ketosis with ketoacidosis. Diabetic ketoacidosis is a dangerous condition affecting people who lack insulin and is primarily seen in type 1 diabetes or insulin-dependent type 2 diabetes. In diabetic ketoacidosis, ketones levels are higher than in the ketosis produced by diet. In a state of diabetic ketoacidosis, ketone bodies can reach dangerously high levels and the blood's pH changes, becoming acidic. In an effort to clear up confusion about the two conditions, sometimes ketosis is referred to as "nutritional ketosis."

Myth: On a ketogenic diet, you can eat whatever fatty foods you want, such as bacon, cheese, French fries, and ice cream.

While it is true that a ketogenic diet includes primarily fatty foods, many foods that are high in fat are also high in carbohydrate. For example, foods such as ice cream and French fries are high in fat but they are also high in starch (French fries) and sugar (ice cream). So these foods would not be recommended in a keto diet plan.

Myth: On a ketogenic diet, you eat a lot of meat.

Actually, keto diets include less meat than you might imagine. Eating foods high in protein can offset the macronutrient balance required to reach and maintain ketosis. For example, a hamburger patty is high in fat but higher in protein. If you boost your protein intake, your body may burn protein as fuel instead of fat (a process called gluconeogenesis).

Myth: You can't be a vegetarian and go on a ketogenic diet.

While it is more difficult to be a vegetarian and go on a ketogenic diet, it is not impossible. However, there are fewer plant sources of fat than there are dairy and meat sources of fat. So your food variety will be limited.

Myth: On a ketogenic diet, you don't have to count calories.

Most ketogenic diets don't require you to limit calories. So while you don't count calories per se, you do need to watch and calculate your macronutrient intake on a ketogenic diet, especially in the beginning of the program when you are trying to get your body into ketosis. Macronutrients such as fat, carbohydrates, and protein are different types of calories.

How It Compares

If you're considering the ketogenic diet, it can be helpful to evaluate how it compares to other diets used in medical, athletic, and weight loss settings.


  • Allows for higher consumption of fat during Phase 1 of the program
  • Limits carbohydrate intake
  • Includes some keto-friendly foods in the food plan
  • Encourages higher consumption of low-glycemic carbohydrates in later phases of the diet

Low-carbohydrate diets

  • All variations restrict carbohydrate intake, although generally not as much as the ketogenic diet. Most low-carb diets recommend an intake of at least 20–30% of your calories from carbs—much higher than that of a keto diet.
  • Meals are often built around vegetables and fat intake is usually not restricted.

Scarsdale diet

  • This diet was also developed in a medical setting, popular in the 1970s, often compared to Atkins, and promised quick weight loss
  • The eating program was highly restrictive, limiting both calories and carbohydrates. However, those who consumed this diet ate more foods high in protein.
  • The Scarsdale diet is no longer as popular as it once was due, in part, to the criticism it received from nutrition experts.

The ketogenic diet varies substantially from nutritional guidelines provided by the U.S. Department of Agriculture (USDA). According to the 2020–2025 Dietary Guidelines for Americans, adult men and women are advised to consume only 20% to 35% of calories from fat with an emphasis on healthy fat. They advise that adults consume 45% to 65% of calories from carbohydrate and 10% to 35% of calories from protein.

Additionally, the USDA provides a recommendation for dietary fiber (approximately 22–34 grams per day). Those on a ketogenic diet would have a difficult time reaching this goal since fiber is a carbohydrate.

A Word From Verywell

The ketogenic diet is a helpful strategy for some people in the management of certain neurological conditions. It has also been used in the short term for the treatment of diabetes and obesity. Some people have also found success with this eating style in their efforts to reach and maintain their goal weight. However, it is widely recognized as a difficult lifestyle to maintain, simply because the standard American diet is heavy in carbohydrate-rich foods.

If you want to try a ketogenic diet, be aware that you'll have to adjust it for your individual metabolism and experiment with the right balance of carbs and calories. You may want to consult a registered dietitian to build keto-friendly menus that will meet your nutritional needs. Be sure to keep your health care provider informed when you start a new diet, especially if you have ongoing health conditions.

15 Sources
Verywell Fit uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Additional Reading
  • McDonald, T., & Cervenka, M. C. (2018). The Expanding Role of Ketogenic Diets in Adult Neurological Disorders. Brain sciences8(8), 148. doi:10.3390/brainsci8080148

  • SHARMAN, M. J., & VOLEK, J. S. (2004). Weight loss leads to reductions in inflammatory biomarkers after a very-low-carbohydrate diet and a low-fat diet in overweight men. Clinical Science, 107(4), 365–369. doi:10.1042/cs20040111

  • Stafstrom, C. E., & Rho, J. M. (2012). The ketogenic diet as a treatment paradigm for diverse neurological disorders. Frontiers in pharmacology3, 59. doi:10.3389/fphar.2012.00059

  • Wheless, J. W. (2004). History and Origin of the Ketogenic Diet. Epilepsy and the Ketogenic Diet, 31–50. doi:10.1007/978-1-59259-808-3_2

  • Atkins, Robert C. Dr. Atkins New Diet Revolution, Revised Edition. New York: Harper Collins. 2009.
  • Paoli, A et al. Beyond weight loss: a review of the therapeutic uses of very-low-carbohydrate (ketogenic) diets. European Journal of Clinical Nutrition. May 2014; Epub ahead of print. doi:10.1038/ejcn.2013.116
  • Volek, Jeff S., and Phinney, Stephen The Art and Science of Low Carbohydrate Performance. Beyond Obesity LLC. 2012.

By Laura Dolson
Laura Dolson is a health and food writer who develops low-carb and gluten-free recipes for home cooks.