The ketogenic diet is a high-fat, moderate-protein, low-carbohydrate eating pattern that was originally developed to treat epileptic children by mimicking a starvation state.
Rather than using glucose—from sugars and carbohydrates in the diet—as energy, a ketogenic diet forces the body to use ketones made from dietary fat by the liver.
Critics say the diet is high fat, low fiber, high cholesterol, bad for gut health, and unsuitable for women, particularly before the menopause, who need carbohydrates to make hormones such as progesterone.
But nutritional therapist Moira Newiss told Newsweek that she disagrees. Having been on the ketogenic diet for more than five years, she said it was perfectly suitable for women.
"As someone who had severe burnout, chronic fatigue and a number of mental-health problems, a ketogenic diet has effectively fueled my brain and body so that all my health problems have stayed in remission," she said.
"Although I had started to feel much better by going low-carb and introducing stress management strategies, I only got back 100 percent of my energy and mental clarity when I went ketogenic.
"Then, I could climb mountains and race my bike, and got rid of all my brain fog."
One of the advantages of the ketogenic diet is that it eliminates the body's reliance on glucose for energy, so some people find they have steadier energy levels—or, in Newiss' case, more energy overall.
"I gave it a go because I wanted to feel like a teenager again," she said. "I wanted to have boundless energy and feel full of vitality."
She said that, in ketosis—when the liver is producing ketones from fat for energy—the mitochondria in cells can more efficiently make adenosine triphosphate (ATP): the fuel that the body works on, made from glucose or ketones.
Not everybody agrees that this process is more efficient with ketones than glucose, but Newiss said that it is, especially for the brain.
Newiss also said that the ketogenic diet was more anti-inflammatory than glucose-based eating, and produced more energy—all of which is disputed by some other nutrition experts.
Another source of debate in the nutrition world, addressed by Newiss, is the suitability of the ketogenic diet for women.
Some nutrition experts, particularly those that specialize in women's health, warn that certain hormones such as progesterone—a key female sex hormone, alongside estrogen—rely on carbohydrates.
"I think there are a lot of misunderstanding and myths out there about ketogenic diets," said Newiss. "One myth is that it will harm women's hormones, and I that is just what it is: a myth."
She explained that research was still developing in that area, but that some evidence on women's thyroids—which produces hormones—suggested that the ketogenic diet might reduce hormone demand and increase sensitivity in the thyroid, implying that the body adapted to a ketogenic diet in a positive way.
"There are also other myths, such as a ketogenic diet adversely affecting the gut microbiome," said Newiss. "The gut microbiome is highly complex, and we are still to discover and understand how all the different microbes work together and interact with the gut lining and our immune system.
"Yes, the ketogenic diet will change the gut microbiome, but it changes all the time. This does not mean it is a bad thing."
Newiss said that many of the studies that had shown negative effects associated with ketogenic diets were flawed, because they were done by feeding mice a lot of poor-quality fats, high in omega 6, which is widely believed to be inflammatory.
"Many studies that use this type of ketogenic diet find it promotes inflammation, which is not surprising!" she said. "If you eat natural fats, then inflammation reduces."
Newiss recommended following a ketogenic diet comprised of fat from eggs, avocados, coconut, meat, dairy, nuts, seeds, fish and olive oil; protein from meat, dairy and legumes; and less than 50 grams (1.7 ounces) of carbohydrates, from low-starch vegetables, such as kale, and low-sugar fruits, such as berries.
She said that many think ketogenic diets are nutrient poor, but that this was only true if someone eating poorly; following it well, she said, could provide enough nutrients.
Saturated fat is another key talking point when it comes to reasons to avoid a ketogenic diet, but Newiss said that the evidence indicated: "there is no scientific ground to demonize saturated fats as a cause of heart disease."
This is an ongoing nutrition debate; does saturated fat cause heart disease, or are sugar and ultra-processed food really to blame?
"Even today, many people continue to think fat is the problem, despite growing mountains of evidence that sugar and carbohydrates are the more likely villain," said Newiss.
"The concern around saturated fat was to do with cholesterol and the heart-health hypothesis that cholesterol from saturated fat caused heart disease.
"Increased total cholesterol is not associated with increased cardiovascular risk. Not only that, but cholesterol is also vitally important for your health especially as you age, and a higher cholesterol is associated with longevity."
However, Newiss did say that ketogenic diets were not suitable for everybody, and she did not recommend them for all her nutrition clients.
"I would always advise that women seek professional help before starting a ketogenic diet if they are taking medication," she said.
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