The main difference between a ketogenic diet and a broader low-carbohydrate diet is how severely carbohydrates are restricted.
A low-carbohydrate diet can take several forms and does not have one universally accepted carbohydrate limit. Some clinical sources classify a low-carb diet as providing less than 26% of daily calories from carbohydrates, while ketogenic diets are considerably more restrictive and are designed to put the body into a state called ketosis.
A ketogenic diet typically provides about 70% to 80% of its calories from fat, 10% to 20% from protein and 5% to 10% from carbohydrates. Many versions restrict carbohydrates to fewer than 50 grams a day, although the amount needed to reach ketosis varies from person to person.
The two approaches can both reduce carbohydrate intake, but they are not interchangeable.
What is a ketogenic diet?
A ketogenic, or keto, diet is a very low-carbohydrate, high-fat eating pattern that is intended to put the body into nutritional ketosis.
Normally, carbohydrates are broken down into glucose, which provides much of the body’s energy. When carbohydrate intake is severely restricted, the liver produces ketone bodies from fat. These ketones can then be used as an alternative source of energy by the body and brain.
Nutritional ketosis is different from diabetic ketoacidosis, a dangerous medical condition in which ketone levels become excessively high and the blood becomes acidic. Ketoacidosis occurs most commonly in people with type 1 diabetes, although rare cases have also been reported in people without diabetes.
The ketogenic diet was originally developed for medical purposes, particularly to help control difficult-to-treat epilepsy in children. It has since attracted attention as a dietary approach to weight management and metabolic health.
What is a low-carbohydrate diet?
A low-carbohydrate diet simply reduces the amount of carbohydrate eaten compared with a conventional diet. Unlike keto, it does not necessarily aim to produce ketosis.
There are several versions of low-carb diets, with differences in how much carbohydrate, protein and fat they contain. Some allow substantial amounts of vegetables, fruit, whole grains and other carbohydrate-containing foods while reducing refined carbohydrates and added sugars.
This makes low-carb a broader category than keto. A person can follow a low-carbohydrate eating pattern without eating few enough carbohydrates to enter ketosis.
How do the diets affect weight?
Both low-carbohydrate and ketogenic diets can result in weight loss for some people, particularly in the short term. But the evidence does not show that severely restricting carbohydrates is necessarily superior over the long term.
Mayo Clinic says very low-carbohydrate diets can produce greater short-term weight loss than low-fat diets, but studies generally find that the difference becomes smaller at 12 or 24 months. Harvard researchers have similarly found that different dietary approaches can produce comparable long-term results.
Early weight loss on a ketogenic diet can also include a substantial loss of water as the body’s stored carbohydrate, or glycogen, declines. That means changes on the scale at the beginning do not necessarily represent an equivalent loss of body fat.
Weight management is influenced by several factors, including overall energy intake, food quality, physical activity, sleep, individual metabolism and how sustainable an eating pattern is over time.
What about insulin?
The original article places much of its explanation of weight loss around insulin and describes insulin as putting the body into “fat storage mode.” That is an oversimplification.
Insulin is a hormone that helps regulate blood glucose and allows cells to take up glucose from the bloodstream. Its levels naturally change in response to eating, particularly after carbohydrate-containing foods.
Reducing carbohydrate intake can lower blood glucose and insulin levels, particularly in people with insulin resistance or diabetes. But this does not mean that insulin alone determines whether a person gains or loses body fat.
What are the possible benefits?
Research suggests that low-carbohydrate eating patterns can improve some metabolic measures in certain people.
Studies have reported improvements in blood triglycerides and, in some circumstances, blood glucose and blood pressure. However, the effects depend on the foods replacing carbohydrates. Low-carbohydrate diets built around vegetables, nuts, seeds, fish and other healthier sources of fat and protein may have a different health profile from diets dominated by processed meat and saturated fat.
The evidence for ketogenic diets as a long-term general weight-management strategy remains less certain. Harvard notes that many studies have been relatively short and that longer-term adherence can be difficult.
What are the drawbacks?
The restrictive nature of a ketogenic diet can make it difficult to maintain. Cutting carbohydrates sharply can cause temporary symptoms such as headaches, fatigue, constipation, muscle cramps and weakness.
Severely restricting carbohydrates can also reduce intake of foods that provide fiber, vitamins and minerals, including some fruits, whole grains, legumes and vegetables. A poorly planned diet can therefore create nutritional gaps.
The type of fat consumed also matters. A ketogenic diet that relies heavily on saturated fats can raise concerns about cardiovascular health, while unsaturated fats from foods such as nuts, seeds, avocados, plant oils and oily fish provide a different nutritional profile.
The long-term health effects of ketogenic diets are still not fully established.
Which approach is better?
There is no single diet that is appropriate for everyone.
A low-carbohydrate diet is a broader approach and can allow a greater variety of foods than a strict ketogenic diet. Keto is considerably more restrictive because it is designed to maintain ketosis.
For someone considering a major change in eating patterns, the choice should take into account overall nutrition, existing medical conditions, medications, food preferences and whether the diet can be followed safely over time. Mayo Clinic recommends discussing a low-carbohydrate weight-management diet with a health professional, particularly for people with conditions such as diabetes, heart disease or kidney disease.
The most important distinction is therefore straightforward: all ketogenic diets are low-carbohydrate diets, but not all low-carbohydrate diets are ketogenic. Keto requires carbohydrate restriction severe enough to produce ketosis, while a low-carb diet does not necessarily do so.
