Adopting a ketogenic diet may also hamper athletic performance, says Weiss, even though many athletes try it, thinking it will have the opposite effect. In a recent study in the Journal of Sports Medicine and Physical Fitness, Weiss and his colleagues found that after four days on a keto diet, participants performed worse on anaerobic exercise tasks—which involve short bursts of intense activity—than those who’d recently gone on a high-carb diet.
A study with an intent-to-treat prospective design was published in 1998 by a team from the Johns Hopkins Hospital[20] and followed-up by a report published in 2001.[21] As with most studies of the ketogenic diet, no control group (patients who did not receive the treatment) was used. The study enrolled 150 children. After three months, 83% of them were still on the diet, 26% had experienced a good reduction in seizures, 31% had had an excellent reduction, and 3% were seizure-free.[Note 7] At 12 months, 55% were still on the diet, 23% had a good response, 20% had an excellent response, and 7% were seizure-free. Those who had discontinued the diet by this stage did so because it was ineffective, too restrictive, or due to illness, and most of those who remained were benefiting from it. The percentage of those still on the diet at two, three, and four years was 39%, 20%, and 12%, respectively. During this period, the most common reason for discontinuing the diet was because the children had become seizure-free or significantly better. At four years, 16% of the original 150 children had a good reduction in seizure frequency, 14% had an excellent reduction, and 13% were seizure-free, though these figures include many who were no longer on the diet. Those remaining on the diet after this duration were typically not seizure-free, but had had an excellent response.[21][22]

Heart disease: The diet emphasizes eating a lot of fat. If you eat too much saturated fat (the kind in foods like bacon and butter), that could raise your cholesterol, especially LDL, which is linked to heart disease. This is a special concern for people with diabetes, since the condition itself makes you more likely to get heart disease. Make sure that healthier sources are providing your fats -- the mono- and polyunsaturated kinds, such as those in foods like avocados, nuts, and olive and canola oils. If you do it right, your LDL cholesterol and triglyceride levels could go down. If you take medicine for heart problems, such as high blood pressure, check with your doctor to see if you need to make changes to your medications.


Although many hypotheses have been put forward to explain how the ketogenic diet works, it remains a mystery. Disproven hypotheses include systemic acidosis (high levels of acid in the blood), electrolyte changes and hypoglycaemia (low blood glucose).[19] Although many biochemical changes are known to occur in the brain of a patient on the ketogenic diet, it is not known which of these has an anticonvulsant effect. The lack of understanding in this area is similar to the situation with many anticonvulsant drugs.[56]
A survey in 2005 of 88 paediatric neurologists in the US found that 36% regularly prescribed the diet after three or more drugs had failed, 24% occasionally prescribed the diet as a last resort, 24% had only prescribed the diet in a few rare cases, and 16% had never prescribed the diet. Several possible explanations exist for this gap between evidence and clinical practice.[34] One major factor may be the lack of adequately trained dietitians who are needed to administer a ketogenic diet programme.[31]
Why the heck does it happen? Normally, the body uses glucose—or sugar—as its main source of energy. When you cut your carbs below 50 grams per day (the typical threshold for a ketogenic diet), you enter a metabolic state called ketosis: Instead of burning carbs for fuel, your body begins burning ketones—an alternative fuel source that the liver makes by breaking down fat. In turn, this can make you feel run down.
By default, your body burns glucose (carbs) as its primary energy source, but when you switch to an extremely low carb diet, your body will begin to burn fatty acids for energy instead. Fat is your body’s secondary or “backup” fuel source, which can only be tapped when there’s not enough glucose in your diet. When your body begins burning fat as fuel instead of carbs, you’ve entered the metabolic state known as ketosis (1).
Increasing your sodium intake. This will help counteract the water loss that happens when starting a keto diet and replenish sodium. Salt your food heavily; you don’t have to worry about it increasing your blood pressure, because when you’re on a low-carb diet, your insulin stays stable and low, which sends a signal for your kidneys to continuously excrete sodium[*]. 
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.)
Cynthia Sass, MPH, RD, Health’s contributing nutrition editor, says that many of her clients who have tried the ketogenic diet have also reported irritability and changes in mood. And while people don’t necessarily feel hungry on the keto diet—thanks to its high allowance for fat and moderate amounts of protein—some do report serious sugar cravings.
The ketone bodies are possibly anticonvulsant; in animal models, acetoacetate and acetone protect against seizures. The ketogenic diet results in adaptive changes to brain energy metabolism that increase the energy reserves; ketone bodies are a more efficient fuel than glucose, and the number of mitochondria is increased. This may help the neurons to remain stable in the face of increased energy demand during a seizure, and may confer a neuroprotective effect.[56]

In addition to keeping you adequately hydrated -- which can also help alleviate constipation -- drinking lots of water can also help offset still another low-carb diet problem: bad breath. The ketones produced during the diet can lead to what is sometimes described as a fruity odor although it is often described as having an almost "chemical" odor similar to acetone or nail polish remover.
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.
From a genetic perspective, certain people are less metabolically flexible because they have genetic variations (e.g., insufficient production of specific enzymes) that make it more difficult for them to adapt to the ketogenic diet. In contrast, those who are quick keto-adapters may be gifted with genes that enhance their ability to switch between fuel sources more efficiently.
Severely restricting carbohydrates to less than 0.7 ounces (20 grams) a day can result in a process called ketosis. Ketosis occurs when you don't have enough sugar (glucose) for energy, so your body breaks down stored fat, causing ketones to build up in your body. Side effects from ketosis can include nausea, headache, mental and physical fatigue, and bad breath.
It is possible to combine the results of several small studies to produce evidence that is stronger than that available from each study alone—a statistical method known as meta-analysis. One of four such analyses, conducted in 2006, looked at 19 studies on a total of 1,084 patients.[23] It concluded that a third achieved an excellent reduction in seizure frequency and half the patients achieved a good reduction.[18]
The keto diet emphasizes weight loss through fat-burning. The goal is to quickly lose weight and ultimately feel fuller with fewer cravings, while boosting your mood, mental focus and energy. According to keto proponents, by slashing the carbs you consume and instead filling up on fats, you safely enter a state of ketosis. That’s when the body breaks down both dietary and stored body fat into substances called ketones. Your fat-burning system now relies mainly on fat – instead of sugar – for energy. While similar in some ways to familiar low-carb diets, the keto diet’s extreme carb restrictions – about 20 net carbs a day or less, depending on the version – and the deliberate shift into ketosis are what set this increasingly popular diet apart. In fact, other eating plans are pulling in keto elements, so you can find versions like eco-keto and at least one commercial diet that incorporates keto-friendly products.
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