Josh Axe, a doctor of natural medicine and clinical nutritionist, estimates that about 25% of people who try a ketogenic diet experience these symptoms, with fatigue being the most common. “That happens because your body runs out of sugar to burn for energy, and it has to start using fat,” he says. “That transition alone is enough to make your body feel tired for a few days.”
I've been researching the ketogenic diet for quite awhile so when I started this book, I was a little skeptical that there was anything else I could learn. I was wrong. Craig and Maria have done a wonderful job breaking down the science in a way that's easy to understand. Their knowledge and experience show you how to be successful on keto and how to break through plateaus so you can achieve your health goals. This isn't a "this is how keto works for me and my body so it should work for you too" book, it's a "this is how the human body works, how keto affects the human body, and how you can be successful with keto all based on science". There are also chapters dedicated to discussing the benefits of keto and how to heal your body - it's not all about weight loss. I knew keto was a good way to eat, but I had no idea how many syndromes, diseases, and even cancers that can be reversed through a clean keto diet.
Other forms of ketogenic diets include cyclic ketogenic diets, also known as carb cycling, and targeted ketogenic diets, which allow for adjustments to carbohydrate intake around exercise. These modifications are typically implemented by athletes looking to use the ketogenic diet to enhance performance and endurance and not by individuals specifically focused on weight loss.

Staying in Ketosis long-term: Chronic Ketosis can cause fatigue, muscle soreness, insomnia and nausea. "Unless you have a medical condition that requires you to stay in Ketosis for long-term, you shouldn't stay in that state for a prolonged period without any carb ups," Mavridis suggests. And if you're a beginner, "it’s recommended that you go through the fat-adaptation phase so that your body becomes accustomed to burning both glucose and fat for fuel," says the nutritionist.
Because it lacks carbohydrates, a ketogenic diet is rich in proteins and fats. It typically includes plenty of meats, eggs, processed meats, sausages, cheeses, fish, nuts, butter, oils, seeds, and fibrous vegetables. Because it is so restrictive, it is really hard to follow over the long run. Carbohydrates normally account for at least 50% of the typical American diet. One of the main criticisms of this diet is that many people tend to eat too much protein and poor-quality fats from processed foods, with very few fruits and vegetables. Patients with kidney disease need to be cautious because this diet could worsen their condition. Additionally, some patients may feel a little tired in the beginning, while some may have bad breath, nausea, vomiting, constipation, and sleep problems.

Normal dietary fat contains mostly long-chain triglycerides (LCT). Medium-chain triglycerides are more ketogenic than LCTs because they generate more ketones per unit of energy when metabolised. Their use allows for a diet with a lower proportion of fat and a greater proportion of protein and carbohydrate,[3] leading to more food choices and larger portion sizes.[4] The original MCT diet developed by Peter Huttenlocher in the 1970s derived 60% of its calories from MCT oil.[15] Consuming that quantity of MCT oil caused abdominal cramps, diarrhoea and vomiting in some children. A figure of 45% is regarded as a balance between achieving good ketosis and minimising gastrointestinal complaints. The classical and modified MCT ketogenic diets are equally effective and differences in tolerability are not statistically significant.[9] The MCT diet is less popular in the United States; MCT oil is more expensive than other dietary fats and is not covered by insurance companies.[3]
One downside to a ketogenic diet for weight loss is the difficulty maintaining it. “Studies show that weight loss results from being on a low-carb diet for more than 12 months tend to be the same as being on a normal, healthy diet,” says Mattinson. While you may be eating more satiating fats (like peanut butter, regular butter, or avocado), you’re also way more limited in what’s allowed on the diet, which can make everyday situations, like eating dinner with family or going out with friends, far more difficult. Because people often find it tough to sustain, it’s easy to rely on it as a short-term diet rather than a long-term lifestyle.
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