On a ketogenic diet, your entire body switches its fuel supply to run mostly on fat, burning fat 24-7. Insulin levels become very low, and fat burning increases dramatically. It becomes easy to access your fat stores to burn them off. This is great if you’re trying to lose weight, but there are also other less obvious benefits, such as less hunger and a steady supply of energy. This may help keep you alert and focused.
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.
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,[34] 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.[35] On the other hand, 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] A person with a disorder of fatty acid oxidation is unable to metabolise fatty acids, which replace carbohydrates as the major energy source on the diet. On the ketogenic diet, their body would consume its own protein stores for fuel, leading to ketoacidosis, and eventually coma and death.[36]
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.”
The only issue with keto, is really that I’m afraid that it might be hard to up my calories to a maintenance weight now that I’ve gotten a taste preference for the rich assortment of foods with no carbs in them. I’m satisfied with less calories than I will need after my excess fat is burned off… but , maybe I bet my body will send more hunger signs once there isn’t anymore body fat in the cupboard to use instead of what goes down my throat.
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.
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.

In Asia, the normal diet includes rice and noodles as the main energy source, making their elimination difficult. Therefore, the MCT-oil form of the diet, which allows more carbohydrate, has proved useful. In India, religious beliefs commonly affect the diet: some patients are vegetarians, will not eat root vegetables or avoid beef. The Indian ketogenic diet is started without a fast due to cultural opposition towards fasting in children. The low-fat, high-carbohydrate nature of the normal Indian and Asian diet means that their ketogenic diets typically have a lower ketogenic ratio (1:1) than in America and Europe. However, they appear to be just as effective.[53]


Yancy WS Jr, Westman EC, McDuffie JR, Grambow SC, Jeffreys AS, Bolton J, Chalecki A, Oddone EZ, “A randomized trial of a low-carbohydrate diet vs orlistat plus a lowfat diet for weight loss,” Arch Intern Med. 2010 Jan 25;170(2):136-45. http://www.ncbi.nlm.nih.gov/pubmed/20101008?itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum&ordinalpos=2.
In terms of weight loss, you may be interested in trying the ketogenic diet because you’ve heard that it can make a big impact right away. And that’s true. “Ketogenic diets will cause you to lose weight within the first week,” says Mattinson. She explains that your body will first use up all of its glycogen stores (the storage form of carbohydrate). With depleted glycogen, you’ll drop water weight. While it can be motivating to see the number on the scale go down (often dramatically), do keep in mind that most of this is water loss initially.
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