Those issues can be part of what's known as the “keto flu,” Warren says. Other side effects of the keto diet, all of which are tied to carb withdrawal, can include lightheadedness, nausea, mental fog, cramps, and headaches, in addition to tiredness. Luckily, the keto flu doesn't usually last more than a week—which is coincidentally about when people start to see the number on the scale go down, says Warren.
Because the ketogenic diet alters the body's metabolism, it is a first-line therapy in children with certain congenital metabolic diseases such as pyruvate dehydrogenase (E1) deficiency and glucose transporter 1 deficiency syndrome,[35] which prevent the body from using carbohydrates as fuel, leading to a dependency on ketone bodies. The ketogenic diet is beneficial in treating the seizures and some other symptoms in these diseases and is an absolute indication.[36] However, it is absolutely contraindicated in the treatment of other diseases such as pyruvate carboxylase deficiency, porphyria, and other rare genetic disorders of fat metabolism.[9] Persons with a disorder of fatty acid oxidation are unable to metabolise fatty acids, which replace carbohydrates as the major energy source on the diet. On the ketogenic diet, their bodies would consume their own protein stores for fuel, leading to ketoacidosis, and eventually coma and death.[37]
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You’re transitioning. Your body is equipped to process a high intake of carbs and a lower intake of fat. Your body needs to create enzymes to be able to do this. In the transitional period, the brain may run low on energy which can lead to grogginess, nausea, and headaches. If you’re having a large problem with this, you can choose to reduce carb intake gradually.

When you approach your normal body weight, the weight loss will slow. Just remember, a “normal” body weight differs from person to person depending on our genetics and environmental exposures and may not fit what we see in the popular media. The weight loss won’t go on forever. As long as you follow the advice to eat when you are hungry, you will eventually stabilize your weight.


Wondering what fits into a keto diet — and what doesn’t? “It’s so important to know what foods you’ll be eating before you start, and how to incorporate more fats into your diet,” says Kristen Mancinelli, RD, author of The Ketogenic Diet: A Scientifically Proven Approach to Fast, Healthy Weight Loss, who is based in New York City. We asked her for some guidelines.

When you eat foods high in carbohydrates and fat, your body naturally produces glucose. Carbohydrates are the easiest thing for the body to process, and therefore it will use them first – resulting in the excess fats to be stored immediately. In turn, this causes weight gain and health problems that are associated with high fat, high carbohydrate diets (NOT keto).
Also make sure that you know what foods have mostly carbs, fat, and protein, so you can make the right choices. For instance, it’s not just bread, pasta, chips, cookies, candy, and ice cream that contain carbs. Beans may contain protein, but they’re also very high in carbohydrates. Fruit and veggies also mostly contain carbs. The only foods that don’t contain carbs are meat (protein) and pure fats, like butter and oils (including olive oil and coconut oil).

If you’ve decided to move forward in trying the keto diet, you will want to stick to the parameters of the eating plan. Roughly 60 to 80 percent of your calories will come from fats. That means you’ll eat meats, fats, and oils, and a very limited amount of nonstarchy vegetables, she says. (This is different from a traditional low-carb diet, as even fewer carbs are allowed on the keto diet.)
A simple standby, but one that ketoers adore. 2 or 3 fried eggs and some bacon might not sound like much, but it’s full of protein that will keep you full and energized all morning. Take the opportunity on the weekend to lay your bacon strips on a single cookie sheet and bake in the oven for 20 minutes at 400 degrees. The result is the best bacon you’ve ever had, in a big batch, with no sitting over a popping, hissing frying pan.
During the 1920s and 1930s, when the only anticonvulsant drugs were the sedative bromides (discovered 1857) and phenobarbital (1912), the ketogenic diet was widely used and studied. This changed in 1938 when H. Houston Merritt, Jr. and Tracy Putnam discovered phenytoin (Dilantin), and the focus of research shifted to discovering new drugs. With the introduction of sodium valproate in the 1970s, drugs were available to neurologists that were effective across a broad range of epileptic syndromes and seizure types. The use of the ketogenic diet, by this time restricted to difficult cases such as Lennox–Gastaut syndrome, declined further.[10]
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