How the Diet Works

Carbohydrates are your body’s favorite fuel source; it breaks them down into glucose. Without a steady intake of carbohydrates, your body turns to using protein for fuel.

But if you also are limiting how much protein you eat, your body is forced to burn stored fat as its primary source of fuel. That can result in weight loss, and ketones are a byproduct of burning fat.

The biggest factor in whether or not a diet is ketogenic

is how low in carbohydrates it is. A moderate reduction in carbohydrate can be very helpful to a lot of people, but it won’t be ketogenic. There are three approaches to low-carb eating and only one of which focuses on ketosis as a goal throughout the diet.Diets such as the Atkins Diet start out as a very low-carb ketogenic diet, but as people add carbohydrates, many or most will be eating too much carbohydrate to be in ketosis. It is probably more accurate to talk about the degree to which a diet is ketogenic rather than whether or not a diet is ketogenic.

Understanding Ketosis

Ketosis means that your body is in a state where it doesn’t have enough glucose available to use as energy, so it switches into a state where molecules called ketones are generated during fat metabolism.

Ketones can be used for energy, and have a special property—they can be used instead of glucose for most of the energy needed in the brain, where fatty acids can’t be used. Also, some tissues of the body prefer using ketones, in that they will use them when available (for example, the heart muscle will use one ketone in particular for fuel when possible)

Diet Candidates

In addition to weight loss, ketogenic diets attract interest for a variety of reasons. They are already well-established as a treatment for epilepsy, and researchers are interested in uses for other neurological conditions. Some athletes are experimenting with using a ketogenic diet to enhance endurance.

A 2014 paper in the European Journal of Clinical Nutrition listed the following conditions as possibly being helped by ketogenic diets:

Strong evidence of benefit was found for epilepsy, weight loss, type 2 diabetes, and cardiovascular risk factors (particularly improving triglycerides, HDL cholesterol, and patterns of LDL cholesterol most associated with arterial plaque).

Emerging evidence (some evidence with more research in progress) was seen with other neurological diseases, including Parkinson’s disease, Alzheimer’s disease, narcolepsy, brain trauma, and amyotrophic lateral sclerosis, as well as polycystic ovarian syndrome, acne, and some types of cancer (especially, perhaps, some types of brain cancer)

Calorie Distribution

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

Meals are most often built around fat sources such as fatty fish, meat, nuts, cheese, and oils.

The Ketogenic Diet for Epilepsy (KDE) is a special case of a ketogenic diet. The following are more general guidelines for ketogenic diets.

Carbohydrate: Most of what determines how ketogenic a diet is will depend on how much carbohydrate is eaten, as well the individual’s metabolism and activity level. A diet of less than 50 or 60 grams of net (effective) carbohydrate per day is generally ketogenic. 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 percent of calories from carbs. However, athletes and people with healthy metabolisms may be able to eat 100 or more grams of net carbohydrate in a day and maintain a good level of ketosis. At the same time, an older sedentary person with Type 2 diabetes may have to eat less than 30 net grams to achieve the same level.

Protein: When people first reduce carbohydrates in their diets, it doesn’t seem as though the amount of protein they eat is as important to ketosis as it often becomes later on. For example, people on the Atkins diet often eat fairly large amounts of protein in the early stages and remain in ketosis. However, over time, some (perhaps most) people need to be more careful about the amount of protein they eat as (anecdotally) the bodies of many people seem to “get better” at converting protein into glucose ( gluconeogenesis

When people first reduce carbohydrates in their diets, it doesn’t seem as though the amount of protein they eat is as important to ketosis as it often becomes later on. For example, people on the Atkins diet often eat fairly large amounts of protein in the early stages and remain in ketosis. However, over time, some (perhaps most) people need to be more careful about the amount of protein they eat as (anecdotally) the bodies of many people seem to “get better” at converting protein into glucose ( Fat: Most of the calories in a ketogenic diet come from fat, which is used for energy. The exact amount of fat a person needs to eat will depend on carbohydrate and protein intake, how many calories they use during the day, and whether they are losing weight (using their body fat for energy). Depending on these factors, somewhere in the range of 60-80 percent of calories will come from fats on a ketogenic diet (even up to 90 percent on, for example, the Ketogenic Diet for Epilepsy). People tend not to overeat on diets this high in fat, so calorie counting is rarely necessary.

Types of Fats

When eating this large amount of fat, you can imagine that the types of fats consumed are very important. Many authors advise steering clear of oils that are high in polyunsaturated omega-6 fats (soy, corn, cottonseed, safflower, etc. due to the fact that)

Dr. Stephen Phinney, who has been doing research on ketogenic diets since the 1980s, has observed that people don’t do as well when they are consuming a lot of these oils (mayonnaise and salad dressings are a common source). This could be because omega-6 fats can be inflammatory, especially in large amounts, or some other factor, but people didn’t feel as well or perform as well athletically in his experiments.

On the other hand, fats high in medium-chain triglycerides, such as coconut oil and MCT oil are often encouraged, 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 (often 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 also good choices, as they are high in monounsaturated fats and low in polyunsaturated fats.

Sample Menus

Here are 12 days of nutritionally-complete low-carb menus, all under 50 grams of net carbohydrate per day. They are a good place to get an idea of what a ketogenic diet could look like. These menus are, however, going to be too high in protein for some people to remain in ketosis, and some of them may be a little high in carb if you have very poor carb tolerance. Keep in mind that ketogenic diets should always be tailored to the individual.

Possible Negative Effects

The ketosis produced by fasting or limiting carbohydrate intake does not have negative effects for most people once the body has adapted to that state. It differs from diabetic ketoacidosis

, a dangerous condition affecting people who lack insulin—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.The ketosis caused by diet has been referred to as dietary ketosis, physiological ketosis, benign dietary ketosis (Atkins), and, most recently, nutritional ketosis (Phinney and Volek), in an attempt to clear up possible confusion with ketoacidosis.

There is a transition period while the body is adapting to using fats and ketones instead of glucose as its main fuel. There can be negative symptoms during this period (fatigue, weakness, light-headedness, headaches, mild irritability), but they usually can be eased fairly easily. Most of these symptoms are over by the first week of a ketogenic diet, though some may extend to two weeks.

Athletes who closely track their performance may notice more subtle effects up to 6 to 8 weeks from the start of the diet, and there is some evidence that it may take even longer, up to 12 weeks, for 100 percent adaptation.

Should You Measure Ketones?

Depending on your goals, you may not care. If you are on a low-carb diet and getting the benefits you hoped for, worrying about how high your ketones are may just add a level of complication you don’t need.

Most low-carb diet authors don’t recommend bothering with it. Even many of those who think a ketogenic diet is a good thing just assume that a very-low-carbohydrate diet (under about 50 net grams of carbohydrate) is ketogenic. On the other hand, many people have found that monitoring their ketones, at least for a while, provides valuable information.

It often takes two to four weeks to consistently achieve the target ketone levels of nutritional ketosis, especially because diet tweaking is often necessary.

How to Measure Ketones

People who have studied nutritional ketosis generally advise aiming for a target of a blood ketone level of .5 mmol/L – 3 mmol/L, though it can go as high as 5 without problems.

Measuring blood ketones is the most reliable method. There is a home blood test you can use, but the strips can be very expensive. An alternative is to measure ketones in the urine with a dipstick test, which is much more accessible and inexpensive. However, this method is much less reliable and as time goes on and the body adapts to ketosis, it becomes even less reliable.

A Word From Verywell

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. While some low-carbohydrate dieters find they are able to break stalls in their weight loss, others find that it is more difficult for them to stay in this state. You may want to consult a registered dietitian to build keto-friendly menus for you 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.