Even when exercising at a submaximal level (for example, biking at a moderate speed), heart rate and adrenaline levels rise more when people are eating a high-fat, low-carbohydrate diet[4] vs. a high-carbohydrate, low-fat diet. This results in those on the high fat diet perceiving that they are working harder to achieve the same pace as the high-carbers, and they have much more difficulty speeding up their pace in sprints or climbs.

First, that study, which was reported upon widely, was on mice. Mice are not like humans in the way they fatten or contract metabolic diseases. Journalists/media should stop reporting on mice stories as if they were applicable to humans, especially when there is such a large body of clinical trial data on humans. Let’s be clear: rigorous clinical trial data on humans trumps any data on mice. Every time. And what does the rigorous data on humans say?
Weight loss is the primary reason my patients use the ketogenic diet. Previous research shows good evidence of a faster weight loss when patients go on a ketogenic or very low carbohydrate diet compared to participants on a more traditional low-fat diet, or even a Mediterranean diet. However, that difference in weight loss seems to disappear over time.
The ketogenic diet is indicated as an adjunctive (additional) treatment in children and young people with drug-resistant epilepsy.[26][27] It is approved by national clinical guidelines in Scotland,[27] England, and Wales[26] and reimbursed by nearly all US insurance companies.[28] Children with a focal lesion (a single point of brain abnormality causing the epilepsy) who would make suitable candidates for surgery are more likely to become seizure-free with surgery than with the ketogenic diet.[9][29] About a third of epilepsy centres that offer the ketogenic diet also offer a dietary therapy to adults. Some clinicians consider the two less restrictive dietary variants—the low glycaemic index treatment and the modified Atkins diet—to be more appropriate for adolescents and adults.[9] A liquid form of the ketogenic diet is particularly easy to prepare for, and well tolerated by, infants on formula and children who are tube-fed.[5][30]

Beyond just fat loss, ketosis has an additional benefit in that it spares muscle when you’re eating at a deficit. On a normal diet, when you eat fewer calories than you need for the day, your body breaks down muscle and fat in nearly equal amounts to make up for the difference. With keto, your body is primed to burn mostly fat, particularly if you’re meeting your protein goal for the day. This results in a better metabolism and more total fat lost. Low carb recipes offer:

Ketoacidosis, on the other hand, is dangerous. But it’s usually limited to people with type 1 diabetes, striking when their glucose levels rise due to illness or a missed insulin dose. Without insulin, cells can’t take in glucose, so they burn fat for fuel instead, producing exceptionally high ketone levels—much higher than the amount generated by the keto diet. That, in combination with high blood glucose levels, essentially poisons the blood. “It’s very easy to tell the difference between nutritional ketosis, which has no negative symptoms [aside from ‘keto breath,’ which can smell like nail polish remover], and dietary ketoacidosis, which is an illness that requires hospitalization and causes lethargy, abdominal pain, nausea, vomiting, rapid breathing, and lack of appetite,” says William Yancy, MD, program director at the Duke Diet and Fitness Center in Durham, North Carolina.
In essence, it is a diet that causes the body to release ketones into the bloodstream. Most cells prefer to use blood sugar, which comes from carbohydrates, as the body’s main source of energy. In the absence of circulating blood sugar from food, we start breaking down stored fat into molecules called ketone bodies (the process is called ketosis). Once you reach ketosis, most cells will use ketone bodies to generate energy until we start eating carbohydrates again. The shift, from using circulating glucose to breaking down stored fat as a source of energy, usually happens over two to four days of eating fewer than 20 to 50 grams of carbohydrates per day. Keep in mind that this is a highly individualized process, and some people need a more restricted diet to start producing enough ketones.
The benefits above are the most common ones. But there are others that are potentially even more surprising and – at least for some people – life changing. Did you know that a keto diet can help treat high blood pressure, may result in less acne, may help control migraine, might help with certain mental health issues and could have a few other potential benefits?
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