So this is my data. Showing weight and calorie deficit. I track about 85 other things (Cronometer does it automatically), but these two charts show the important parts of my history with keto. I had a honeymoon period, then a sustained weightloss period, then a mini (insert word that rhymes with fall but begins with "st" instead of "f") and then not only did I exit the (insert word that rhymes with fall but begins with "st" instead of "f") , but my weight loss accelerated.
The ketogenic diet is a high-fat, adequate-protein, low-carbohydrate diet that in medicine is used primarily to treat difficult-to-control (refractory) epilepsy in children. The diet forces the body to burn fats rather than carbohydrates. Normally, the carbohydrates contained in food are converted into glucose, which is then transported around the body and is particularly important in fueling brain function. However, if there is little carbohydrate in the diet, the liver converts fat into fatty acids and ketone bodies. The ketone bodies pass into the brain and replace glucose as an energy source. An elevated level of ketone bodies in the blood, a state known as ketosis, leads to a reduction in the frequency of epileptic seizures.[1] Almost half of children and young people with epilepsy who have tried some form of this diet saw the number of seizures drop by at least half, and the effect persists even after discontinuing the diet.[2] There is some evidence that adults with epilepsy may benefit from the diet, and that a less strict regimen, such as a modified Atkins diet, is similarly effective.[1] The most common adverse effect is constipation, affecting about 30% of patients—this was due to fluid restriction, which was once a feature of the diet, but this led to increased risk of kidney stones and is no longer considered beneficial.[2][3]
The ketogenic diet for weight loss is based on the idea that driving the body into ketosis will maximize fat loss. Ketosis is a normal metabolic process that occurs when the body does not have enough glucose stores for energy. When these stores are depleted, the body resorts to burning stored fat for energy instead of carbs.  This process produces acids called ketones, which build up in the body and can be used for energy. (2)
Everyone has to find their nutritional sweet spot for producing enough ketones and staying in ketosis, but “the core principle of the diet is to keep carbohydrate intake low enough, so your body continues producing ketones at elevated levels,” says Volek. “Your body adapts to this alternative fuel and becomes very efficient at breaking down and burning fat.”
Take a multivitamin. “Because you are removing grains, the majority of fruit, some vegetables, and a significant amount of dairy from your menu, a multivitamin is good insurance against any micronutrient deficiencies,” says Jadin. Depending on what your individual overall diet looks like, Jadin says you might also need to add a calcium, vitamin D, and potassium supplement.

For athletes, research on the keto diet highlights potential improvements in athletic performance, especially when it comes to endurance activities. An article suggests ketogenic-type diets may allow endurance athletes to rely mostly on stored fat for energy during exercise rather than having to refuel with simple carbohydrates during endurance training and competition while additionally improving recovery times. (10)
As for how it feels to follow the diet, St. Pierre says it will vary from person to person; as with most diet-related things, whether or not a way of eating works is in the eye of the beholder. He’s seen some people feel fine, but that “some clients have found it causes brain fog and lethargy, decreases their performance, disrupts their regular bowel movements, and makes them feel generally crappy,” he says. Some keto adherents also report having pretty atrocious breath, which might be caused by the presence of acetone, a ketone and byproduct of fat metabolism, in exhaled breath.
There are three instances where there’s research to back up a ketogenic diet, including to help control type 2 diabetes, as part of epilepsy treatment, or for weight loss, says Mattinson. “In terms of diabetes, there is some promising research showing that the ketogenic diet may improve glycemic control. It may cause a reduction in A1C — a key test for diabetes that measures a person’s average blood sugar control over two to three months — something that may help you reduce medication use,” she says.
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