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Medically Reviewed
Gaining traction in recent years, the keto diet—also known as the ketogenic diet—is a popular weight loss plan. It gets its name from ketosis, a metabolic process that occurs when your body burns fat rather than carbohydrates.
The ketogenic diet is a high-fat, very-low-carbohydrate eating plan that aims to bring about weight loss by causing your body to enter a state of fat-burning ketosis. Although it’s become popular during the past decade or so as a weight loss strategy, it was originally designed 100 years ago as a way to reduce seizures in people with epilepsy.
The keto diet not only promises weight loss, but also claims to reduce hunger and help balance blood sugar. However, it can be a difficult protocol to follow. “One of the cons of the keto diet is that it has very strict rules,” says Melissa Majumdar, a certified specialist in obesity and weight management and a bariatric coordinator at Emory University Hospital Midtown in Atlanta. “I don’t know anybody who would be able to follow this diet for a long period of time.” It’s also risky for people with certain health conditions.
A keto diet is low enough in carbs and protein and high enough in fat to force the body to burn stored fat instead of consumed carbohydrates for energy. To trigger ketosis, a diet typically must contain a maximum of only 50 grams of carbohydrates per day. (A slice of whole-wheat bread, for example, contains about 15 grams of carbohydrates, and a medium banana contains about 29 grams of carbohydrates.) Overall, carbohydrates contribute fewer than 10% of calories in a keto diet. The remainder comes from fat (70% to 80% of daily calories) and protein (about 10% of daily calories or about ½ gram per pound of body weight).
Your body prefers to burn glucose-containing carbs for energy. When carbohydrate-sourced glucose is not available, your body burns fat instead. To use fat for energy, your liver converts fat to substances known as ketones and burns those instead of glucose. When this process occurs, your body is in a state of ketosis.
Because your body prefers to burn glucose rather than fat, it may resist shifting into ketosis and will not do so unless you adhere strictly to carbohydrate and protein limits. It can take a few days, sometimes longer, to achieve a state of ketosis, and you must continue to limit carbohydrates and protein strictly in order to stay in ketosis. “If you don’t follow the rules, you go out of ketosis,” says Majumdar, who is also a registered dietitian and spokesperson for the Academy of Nutrition and Dietetics.
Various types of diets call themselves keto diets. However, some would be more accurately described as “keto-ish” or low-carb diets because they’re too high in carbohydrates to induce ketosis regularly. True keto diets are very low in carbohydrates, high in fat and moderate in protein.
Well-known keto-style diets include the Atkins and South Beach diet. Other low-carb diets may claim to be keto diets, but unless they include fewer than 50 grams of carbohydrates daily and only a moderate amount of protein, they may not induce ketosis reliably. In addition to limiting carbohydrates, you have to make sure you avoid eating too much protein as well, because protein can interfere with ketosis.
The best foods for the keto diet are those high in fat, low in carbohydrates and moderate in protein, such as:
Here’s what you might eat on a typical day while following a keto diet:
The main health benefits of a keto diet can include:
Weight Loss
Some people do find that a keto diet helps them lose weight. However, what works for one person may not work for another. A comprehensive review of scientific evidence published in 2019 in the Journal of Clinical Lipidology looked at the effect of low-carbohydrate and very low-carbohydrate diets like keto on body weight and other factors. It found that keto-style diets are no better than other types of diets, such as low-fat diets, at bringing about long-term weight loss.
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Less Hunger
There is some evidence that keto-type diets reduce hunger, according to the 2019 Journal of Clinical Lipidology review. The effect may be due to a shift in hunger hormones, such as ghrelin and leptin, as well as insulin. “The high fat content of the keto diet may also be satiating,” Majumdar says.
Blood Sugar Control
Eating fewer carbohydrates can lead your pancreas to secrete less insulin and can lower your blood sugar. This response can be helpful for people with prediabetes, insulin resistance or diabetes. “However, similar results have been shown with other kinds of diets that are easier to follow,” Majumdar says. What’s more, simply cutting down on carbohydrates (rather than drastically reducing them) can often improve blood sugar control, too.
Lower Triglycerides
The keto diet may cause a drop in triglycerides, a type of fat found in your blood. High levels of triglycerides can increase the risk of heart attack and stroke. However, this reduction doesn’t hold up over time. A 2020 review in the journal Cureus found that while the keto diet led to decreases in triglycerides, as well as blood pressure, during the first six to 12 months after starting a keto diet, those effects disappeared after 12 months.
High Saturated Fat
Most keto diets are high in foods that contain saturated fat, such as meat, butter, palm oil and coconut oil. Saturated fat can raise LDL (“bad”) cholesterol, which increases heart disease risk. The American Heart Association recommends limiting saturated fat to 5% to 6% of daily calories, or about 13 grams per day. (A 4-ounce hamburger patty contains 7 grams of saturated fat, and 1 ounce of cheddar cheese contains 6 grams of saturated fat.) Some studies even found an increase in all-cause mortality (death from various causes) in people following keto-type diets.
Poor Diet Quality
Because the keto diet leaves out or limits entire groups of healthy foods, such as most fruit, some types of vegetables, legumes, whole grains and dairy, it may not provide all the nutrients you need. “And because it tends to be low in fiber, it can cause constipation,” Majumdar says.
Health Risks
The keto diet may pose risks for people with various health conditions, including high blood pressure, heart disease, disordered eating, diabetes or kidney disease, according to Majumdar. “This is not a diet that individuals with any type of health condition should be doing on their own,” Majumdar says. “They should be followed by a medical professional or dietitian who can monitor them.”
Keto diet proponents tout the benefits of ketosis-fueled fat burning as a way to rid the body of excess stored fat. However, shifting fuel sources from glucose to fat can cause various unpleasant symptoms. According to Majumdar, ketosis symptoms, which are sometimes referred to as “the keto flu,” may include:
These symptoms usually subside after your body adjusts to being in ketosis. “But if you go out of ketosis, you may experience those symptoms again when you go back into ketosis,” Majumdar says.
Pro tip: A benefit of the keto diet is that it can help reduce your added sugar intake. But you don’t have to follow a keto diet to accomplish this feat, Majumdar says. Cut back on the sweet stuff by reading food labels and limiting or avoiding foods with added sugar. The American Heart Association recommends limiting added sugar to no more than 36 grams per day for men and 25 grams for women.
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Kirkpatrick CF, et al. Review of current evidence and clinical recommendations on the effects of low-carbohydrate and very-low-carbohydrate (including ketogenic) diets for the management of body weight and other cardiometabolic risk factors: A scientific statement from the National Lipid Association Nutrition and Lifestyle Task Force. Journal of Clinical Lipidology. 2019;13:689-711.
Batch JT, Lamsal SP, Adkins M, Sultan S, Ramirez MN. Advantages and Disadvantages of the Ketogenic Diet: A Review Article. Cureus. 2020;12(8):e9639.
Wheless JH. History of the ketogenic diet. Epilepsia. 2008;(49)3-5.
Ketogenic diet. Epilepsy Foundation. Accessed 03/10/2021.
Arnett DK, Blumenthal RS, et al. 2019 ACC/AHA Guideline on the Primary Prevention of Cardiovascular Disease: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines. Circulation. 2019;140:e596–e646.
O’Neill B, Raggi P. The ketogenic diet: Pros and cons. Atherosclerosis. 2020;292:119-126.
Saturated Fat. American Heart Association. Accessed 03/10/2021.
Added sugars. American Heart Association. Accessed 03/10/2021.
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Alice Lesch Kelly is a Boston-based freelance writer specializing in health, nutrition and disease prevention. Her work has appeared in many consumer outlets, including the Berkeley Health After 50 newsletter, the Boston Globe, the New York Times, WebMD and Health Central. She also collaborates on health books with physicians and psychologists. Alice is passionate about helping people make lifestyle changes that improve their physical and mental health.
As an internist and board-certified physician nutrition specialist, Dr. Melina Jampolis specializes in nutrition for weight loss, disease prevention and treatment. She is a former president of the National Board of Physician Nutrition Specialists. She’s also the host of the podcast Practically Healthy With Dr. Melina, is the author of several books including her latest, Spice Up, Live Long, and has appeared on national television programs such as Live With Kelly and Ryan, The Doctors, Dr. Oz and more. She currently maintains a small private nutrition practice in Los Angeles and serves as the chief nutrition officer of blk. water.
