The ketogenic, or keto, diet is a low-carbohydrate, high-fat eating pattern that limits carbohydrates enough to put the body into a metabolic state known as ketosis.
Most versions of the diet restrict carbohydrates to about 20 to 50 grams a day, although the exact amount varies depending on the individual and the type of ketogenic diet being followed.
The diet relies mainly on foods such as meat, fish, eggs, some dairy products, nuts, seeds, avocados, oils and low-carbohydrate vegetables. Foods such as grains, rice, potatoes, sweets and many other carbohydrate-rich foods are generally restricted.
What happens during ketosis
Under normal conditions, the body relies heavily on glucose from carbohydrates for energy. When carbohydrate intake is sharply reduced, the body begins using stored fat and producing ketones, which can then be used as an energy source.
The change can contribute to weight loss for some people. Research also suggests that ketogenic diets can improve some blood sugar measures, although the diet is not appropriate for everyone and its long-term effects remain less certain.
Which foods fit a keto diet?
Low-carbohydrate vegetables can form an important part of a keto eating pattern. Leafy greens, broccoli, cauliflower and other non-starchy vegetables provide fiber and micronutrients without contributing large amounts of carbohydrate.
Avocados are also commonly included because they contain relatively little carbohydrate and provide unsaturated fat.
Nuts and seeds can provide both fat and protein, while fish and seafood offer protein and, in the case of fatty fish such as salmon, omega-3 fats.
Fruit requires more attention because many fruits contain enough carbohydrate to make it difficult to remain within a strict ketogenic range. Some lower-carbohydrate fruits, particularly berries, can fit into certain keto meal plans in controlled portions. Mayo Clinic’s healthier approach to keto, for example, includes berries and some beans while keeping net carbohydrates at about 50 grams per day.
Beans and other legumes are also carbohydrate-containing foods. They are nutritious sources of fiber and other nutrients, but their carbohydrate content means they are limited or excluded from many stricter versions of keto.
Choosing fats
Following keto does not mean that all high-fat foods are equally healthy.
Mayo Clinic recommends emphasizing sources of healthier fats such as extra-virgin olive oil, avocado, salmon, nuts and seeds rather than relying heavily on foods high in saturated fat such as butter, bacon and cream. A diet high in saturated fat can raise LDL, or “bad,” cholesterol.
The quality of the foods included in a keto diet therefore matters. A plan built mainly around processed meats, butter and other sources of saturated fat is different from one that includes fish, vegetables, nuts, seeds and unsaturated oils.
What about intermittent fasting?
Intermittent fasting is a separate eating pattern that limits when a person eats. It is sometimes combined with keto, but fasting is not required to enter ketosis.
Research suggests that intermittent fasting can help some people with weight management, but it is not suitable for everyone. People with certain medical conditions should discuss significant changes to their eating pattern with a health professional.
Potential risks
The keto diet can cause side effects, particularly when someone first begins restricting carbohydrates. These can include headaches, fatigue, constipation, dehydration and bad breath.
Because the diet restricts many fruits, whole grains and legumes, poorly planned versions can also provide insufficient fiber or some vitamins and minerals. Other potential concerns include kidney stones and increases in LDL cholesterol, depending on the foods consumed.
Mayo Clinic also notes that the long-term health risks of a strict keto diet are not fully known and that the restrictive nature of the diet can make it difficult to maintain.
For that reason, people considering a ketogenic diet, particularly those with existing medical conditions or who take medication affecting blood sugar, should discuss the diet with a qualified health professional before making major dietary changes. Some medications used for diabetes can carry particular risks when combined with a ketogenic diet.
The evidence therefore does not support describing keto simply as a universally healthy diet. Its effects depend on the foods chosen, the individual’s health and how the diet is followed.
