As a species, humans possess a kind of superpower: the ability to survive on a remarkably wide variety of foods, allowing us to thrive everywhere from the Amazon rainforest to the Arctic tundra.
Now, thanks to social media, our dietary range is being tested again. TikTok and YouTube have made stars of influencers who tout — often with the help of celebrities — the virtues of various lifestyles from veganism to juicing to subsisting on nothing but meat. Advocates of some of these trends even claim their diets have cured them of serious diseases.
Are any of these extreme diets safe or healthy? Sometimes, for some people, under some circumstances. They can also be risky and are best done under a doctor’s supervision. That’s why physicians should take seriously the possibility that some of these dietary interventions can help people and learn how to guide patients in adopting them safely.
From a nutritional standpoint, the body needs a variety of minerals and vitamins, a certain amount of protein, and, for energy, a combination of carbohydrates and fats. In the mid-20th century, nutrition researchers deemed fats to be harmful, but have since revised that view and now consider a balance between fat and carbohydrates to be best for most people.
Some of the most popular diets — such as the ketogenic, or “keto” diet — eliminate or restrict carbohydrates and rely heavily on fats. The carnivore diet is a more extreme example, eliminating all plant-based foods. While ketogenic diets have helped some people lose weight and keep it off, they can also cause side effects such as nutrient deficiencies and high cholesterol. And alarmingly, despite warnings from doctors, some people are even promoting a carnivore diet for their children.
Vegan diets might help some people feel healthier, as long as they include all the essential vitamins and minerals, as well as plant-based foods that contain healthy fats and complete sources of protein. But it’s also possible to follow a vegan diet that consists primarily of processed food and sugar, which increases the risks of diabetes, heart disease and other health problems. Vegan diets are more environmentally sustainable than diets heavy in meat — but they’re not ideal for everyone.
People sometimes resort to even more extreme diets for quick weight loss or to indulge the illusion that they are being “cleansed.” In a juice cleanse, for example, people may consume no solid food and get calories only from fruit and vegetable juice for a few days or even several weeks.
This might help people who lose a pound or two to fit into a particular outfit for a special occasion, but juicing concentrates the natural sugar in fruit, and scientists have increasingly realized that even natural sugar, in large quantities, can be bad for you.
It’s understandable that people would buy into this trend, since years of heavy advertising convinced the world fruit juice was the healthiest thing you could consume (it isn’t), and the public health community has been far too reluctant to acknowledge its mistake in demonizing fats and pushing a high-carbohydrate diet as best for everyone.
Some may feel better on a juice cleanse because they’ve cut out something that was unknowingly making them feel sick — but in general, any weight lost will quickly return, and your insides won’t be any “cleaner.”
Unfortunately, the only diets that seem to produce lasting, dramatic effects are those that people commit to for life. Evidence dating back to the 1920s, for example, showed that ketogenic diets were highly effective at preventing seizures and helping people with epilepsy live normal lives.
Eric Kossoff, a neurologist at Johns Hopkins University, said this very high-fat diet mimics some of the effects of fasting, which has been understood for centuries to put seizures in remission. The body has two main pathways for generating energy. Most of the time, food is broken down into glucose, which is stored in the liver and can be used as fuel. If the liver has no glucose — because you’re fasting or eating almost no carbohydrates — your body burns fat through a process called ketosis. It’s an important adaptation that allows us to use body fat as a backup fuel source.
The diet fell out of favor in the 1950s, said Kossoff, because new drugs and surgical treatments for epilepsy emerged, and dietary fat was wrongly stigmatized as fattening and artery-clogging. Now ketogenic diets are making a comeback, he said, thanks to patients and their families. He credits a patient advocacy group, the Charlie Foundation, for pushing doctors to re-examine dietary intervention for children who don’t respond to medication. Today, there are ketogenic diet centers for epilepsy all around the world.
Kossoff recently attended a conference of over 400 doctors in Paris discussing keto for epilepsy, as well as their potential for treating other conditions. The diet has shown promise for managing some cases of bipolar disorder, depression and other psychiatric conditions.
But the diet can negatively affect growth and development in children and cause other health problems, he said, and for some people it can cause unwanted weight loss. Most complications, however, can be addressed with supplements or modifications to the diet, he said, reinforcing the importance of having a knowledgeable doctor involved.
Medical supervision was also crucial in a study published last year, which followed people with Type 2 diabetes over five years as they adopted a ketogenic diet, guided by doctors through telehealth. A significant fraction saw their diabetes go into remission — a result that doesn’t occur spontaneously.
There’s a reason patients are leading the doctors in this area: it’s something people can do on their own, and because dietary interventions haven’t been studied beyond a few conditions, there’s still plenty of untapped potential.
Nicholas Norwitz told me that a ketogenic diet gave him relief from debilitating irritable bowel disease. He developed the condition at 21. After trying medications and various diets, he found that a ketogenic approach worked, enabling him to finish a PhD in metabolism at Oxford University and earn an MD from Harvard.
He said he eats lots of fish, eggs and olive oil. He has nothing against the non-starchy plants allowed on a ketogenic diet, but they don’t always agree with him.
But people can and do stick to diets when the stakes are high enough. We don’t all have to eat the same way — and we shouldn’t. Thanks to our species’ superpower — adaptability — we have more options than we think.
F.D. Flam is a Bloomberg Opinion columnist covering science. She is host of the “Follow the Science” podcast.
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