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What is a Ketogenic Diet

Ketogenic Basics and Help on Getting Started

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Updated July 06, 2014

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

high-fat foods

High-Fat Foods Common on Ketogenic Diets

Photo: Getty Images/Joy Skipper
When reading or hearing about low-carb diets, you may have heard the term "ketogenic diet". Increasingly, people have questions about this. Are all low-carb diets ketogenic? Is that a good thing or a bad thing? What constitutes a ketogenic diet? What are the advantages and disadvantages of a ketogenic diet?

Low-Carb Diets are Not Always Ketogenic Diets

The biggest factor in whether or not a diet is ketogenic is how low in carbohydrate it is. A moderate reduction in carbohydrate can be very helpful to a lot of people, but it won't be ketogenic. In What is a Low-Carb Diet?, I outline three approaches to low-carb eating, 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 carbohydrate, 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".

What is Ketosis?

Ketosis means that the body is in a state where it doesn't have enough glucose available to use as energy, so 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, heart muscle will use one ketone in particular for fuel when possible). For more information, see:

Does Ketosis have any Negative Effects?

The ketosis produced by fasting or limiting carbohydrate intake does not have negative effects in most people once the body has adapted to that state. The confusion on this point is mainly due to the fact that people who lack insulin, mainly Type 1 diabetics or insulin-dependent Type 2 diabetics, can get into a dangerous state called diabetic ketoacidosis. In ketoacidosis, ketones levels are much 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.

A second source of confusion is that 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 (fatique, weakness, light-headedness, headaches, mild irritability), but they usually can be eased fairly easily. Most 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 6-8 weeks from the start of the diet, and there is some evidence that it may take even longer, up to 12 weeks, for 100% adaptation.

Why Do People Go on Ketogenic Diets?

Ketogenic diets are becoming more popular, and for a variety of reasons. In addition to weight loss, they are beginning to be studied as a treatment or prevention for other conditions. They are already well-established as a treatment for epilepsy, and researchers are interested in uses for other neurological conditions.. A June 2013 paper in the European Journal of Clinical Nutrition listed the following conditions as possibly being helped by ketogenic diets:

Strong Evidence
  • Epilepsy
  • Overweight and Obesity (weight reduction)
  • Type 2 Diabetes
  • 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)
  • Neurological Diseases other than epilepsy, including Parkinson's Disease, Alzheimer's Disease, narcolepsy, brain trauma, and amyotrophic lateral sclerosis
  • Polycystic Ovarian Syndrome
  • Acne
  • Some types of cancer (especially, perhaps, some types of brain cancer)
In addition, some athletes are experimenting with using a ketogenic diet to enhance endurance.

What Do People Eat on Ketogenic Diet?

(The Ketogenic Diet for Epilepsy 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 how much carbohydrate is eaten, as well the individual's own metabolism and activity level. A diet of less than 50 or 60 grams of net (effective) carbohydrate per day is generally ketogenic. 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, while 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). At that point, each individual needs to experiment to see if too much protein is throwing them out of ketosis and adjust as necessary.

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% of calories will come from fats on a ketogenic diet (even up to 90% 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.

When eating this large amount of fat, you can imagine that the types of fats consumed is very important. Many authors advise steering clear of oils that are high in polyunsaturated omega-6 fats (soy, corn, cottonseed, safflower, etc). Dr. Stephen Phinney, who has been doing research on ketogenic diets since the 1980's, 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 polyunsaturates.

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. However, they are 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. Ketogenic diets always have to be tailored to the individual.

Should I Measure My 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 awhile, provides valuable information.

How Long Does it Take to Get Into Nutritional Ketosis?

It varies, but it often takes 2 to 4 weeks to consistently achieve the target ketone levels of nutritional ketosis, especially because diet tweaking is often necessary.

How High Should My Ketones Be?

People who have studied nutritional ketosis generally advise shooting 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.

How to Measure Your Ketones

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. On the other hand, I know a couple of people who have been measuring urine ketones for years and still find value in it.

Why Might it Be Worth Knowing my Blood Ketones?

As more long-term low-carbers are trying this, some are finding that they are able to break stalls in their weight loss. Probably the most famous person to do this, Jimmy Moore, was able to lose some weight he had initially regained and then go on to lose even more. However, some people find that it is more difficult for them to stay in this state than they are willing to deal with. In any case, if you try it, it will teach you something about how your body works that you may not have known before.

Sources:

Atkins, Robert C. Dr. Atkins New Diet Revolution. New York: Harper Collins. 2002.

Berg JM, Tymoczko JL, Stryer L. Biochemistry. 5th edition. New York: W H Freeman; 2002. (Section 30.2)

Paoli, A et al. Beyond weight loss: a review of the therapeutic uses of very-low-carbohydrate (ketogenic) diets. European Journal of Clinical Nutrition June 26, 2013; Epub ahead of print. doi:10.1038/ejcn.2013.116

Volek, Jeff S. and Phinney, Stephen The Art and Science of Low Carbohydrate Living. Beyond Obesity LLC. 2011.

Volek, Jeff S. and Phinney, Stephen The Art and Science of Low Carbohydrate Performance. Beyond Obesity LLC. 2012.
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