What is the keto diet?

Dear Alice,

I've been hearing a lot on fitness forums about the "keto diet." I don't know that much about it, but it sounds like it's a diet that's extremely low-carb and high-fat. People say they're getting great results by combining keto with exercise, but I don't understand how. Is there any science to support low-carb/high-fat as a good diet plan, or is this a fad?

Dear Reader, 

Just like fashion fads on the runway, fitness and diet trends come and go. It’s smart to ask questions about any diet plan or physical activity regimen, so kudos to you for seeking out additional information! Originally, ketogenic nutrition strategies were developed for treatment of seizure disorders in children and adolescents. The use of the “keto diet” (originally known as the ketogenic diet) as a weight loss strategy is relatively recent. And as far as shedding pounds is concerned, the keto diet seems to be most effective in the short-term, especially when combined with physical activity. However, this diet is also associated with some health risks — so it’s helpful to explore the benefits and potential drawbacks in tandem. 

Your initial conclusions about the keto diet are correct — the structure is based on an extremely low-carbohydrate, high-fat, and high-protein ratio of calorie sources. The body, in response to obtaining calories primarily from fat and protein, works to break down fatty acids for fuel. In contrast, a diet high in carbohydrates primarily relies on glucose (sugar) for energy. Maintaining adequate blood sugar levels, or levels of glucose in the blood stream, helps ensure your brain has enough fuel to work normally. When glucose isn’t readily available, the brain can use ketones for energy. The process of burning fatty acids for energy is called beta-oxidation and produces a byproduct — the ketone molecule. The keto diet is based off of this switch from glucose fuel to ketone fuel. When the body is burning primarily fat, and not glucose, ketones are produced in excess. 

As far as an effective weight loss strategy, the keto diet typically has the most dramatic results within the first four to six weeks due to the dramatic changes in eating habits. Current scientific research on the keto diet shows that those using this plan specifically for weight loss may experience moderate or significant weight loss in the beginning weeks, followed by less dramatic results in subsequent months. According to some reports, individuals who follow a keto diet for eight to twelve weeks may see an additional reduction in body fat. Of the literature available, most sources advise using the keto diet under the supervision of a health care professional because of the restrictive nature and potential side effects. 

Additionally, some people find these types of diets challenging to maintain long-term because of how strict the rules are around what is permissible to eat. Depending on where you read about the keto diet as a weight loss tool, you’re likely to hear varying reports of effectiveness. While initially successful with weight loss goals, over time, people may experience issues such as depleted energy, food cravings, and other side effects that may hinder continued ability to adhere to the diet. Given the specific guidelines of the keto diet, it may be harder to get a diversity of key vitamins and nutrients from food. Because of this, many health care professionals advise incorporating a multivitamin into the diet as well. Dehydration, constipation, and development of kidney stones are also possible side effects of the keto diet. Some initial research on long-term use of the keto regimen shows potential risks of developing insulin resistance and developing diabetes. Use of the keto diet may also lead to elevated cholesterol or high amounts of fat in the liver. And if the ketones build up in the body quickly without being excreted through urine fast enough, the pH of the blood can become drastically altered, which can be fatal. 

You also asked about results due to the combination of the keto diet and physical activity. Historically, there have been mixed conclusions in research studies about whether combining the ketogenic diet with physical activity provides faster weight loss results or impacts athletic performance. The most recent studies seem to imply that keto plus activity may cause the body to burn fat for energy without negatively affecting athletic potential. That said, some study participants did show elevated blood fat levels, which could increase cardiovascular disease risks. 

Want to figure out if the ketogenic plan is appropriate for you? Considering your motivations, wants, desires, and goals may be a great place to start. Do you want to lose weight? If so, why? Is it about health? Is it about how you hope to be viewed by others? Are there multiple ways you can achieve your goals or meet your needs? And if so, what are the costs and benefits of each? If your self-reflection is still pointing in the direction of the ketogenic plan, it may be helpful to consult a health care provider to avoid any potential health consequences and also to tailor the program to your needs. If your goals are weight loss and you want additional related information, there are many ways to achieve sustainable, healthy results. The weight loss or fitness categories of the Go Ask Alice! Nutrition & Physical Activity archives have some additional ideas. 

Last updated Aug 27, 2021
Originally published Jul 18, 2014

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