Some say "cellar door" is the most beautiful phrase in the English language. But to a health and science writer like myself, the most beautiful phrase is actually, "It made my poop float."
My friend Gila* told me at a party recently that she had tried the ketogenic diet, which was originally designed to treat diabetes and epilepsy, and that the high fat content had made her shit buoyant. Of course I had questions: Why try a diet that was originally only supposed to be done in a hospital setting? Wouldn't eating nothing but fat eventually kill you? And would eating too much fat really make your poop float?
A ketogenic diet is any diet that prompts ketosis, a state in which the central nervous system runs on ketone bodies instead of its usual diet of glucose. It's very low carb, moderate protein, and super high fat. Foods that are cool on a keto diet include bacon, heavy whipping cream, and coffee with butter in it, aka bulletproof coffee. Keto is quickly becoming the new eating fad—a natural extension of Atkins and paleo. Only now the miracle food isn't protein; it's fat.
Normally, the body breaks down carbohydrates into glucose, and that's what your brain consumes for energy. By depriving your body of carbs and limiting protein, you force your liver to start breaking down fat (either from fat stores or the butter you just drank) into three ketone bodies: acetoacetate, beta-hydroxybutyric acid, and acetone. Some ketone bodies are consumed for energy, some just hang out in your tissue. The acetone actually leaves the body via the lungs, which gives dieters a nail polish remover scent known as "keto breath."
Read more: I Put My Dog On a Clean Eating Diet
Proponents of the diet say they have experienced increased energy, better memory, and dramatic weight loss. They also say it might cure cancer, but that's a pretty standard claim in the hyperbolic world of nutritional biohacking. Critics of the diet question whether eliminating whole food groups can ever truly be the healthy choice. "The true ketogenic diet is very controlled and limited," says Robert Nellis of the Mayo Clinic. "[It's] just short of starvation."
The ketogenic diet was invented in the early 20th century to treat Type 1 diabetes. "[Type 1] used to be called childhood diabetes, because you didn't live beyond childhood," says Nellis. "It was a death sentence." Before the discovery of insulin, Type 1 diabetes would run unchecked through the patient's body. "A body without insulin is like a furnace without a thermostat," says Nellis, meaning that you can try to course correct, but only for so long.
Since ketosis doesn't run on the same carbohydrate-sugar system, diabetics could prolong their lives on the keto diet, at a cost. "The best known [ketogenic diet] patient was actually the daughter of a Chief Justice of the Supreme Court at the time," says Nellis. "She was a teenager and she weighed like 60 pounds." Her parents jumped at the chance to treat her with insulin rather than a diet that left her a (barely) walking skeleton. Another patient under a ketogenic diet at the time weighed only 45 pounds. "On the true diet, you're lucky if you have the energy to make it out of bed," says Nellis. "The idea that this diet is being used for, in my mind, non-emergency purposes is kind of strange and bizarre."
It's unclear just when the keto diet began its second life as a weight loss regimen. It may have been an extension of the Atkins and Paleo diets, which gained popularity in the early and late 2000s, respectively. In 2012, the New York Times reported on a K-E (Ketogenic Enteral) diet fad among brides. Women hoping to fit into their wedding dresses were allegedly submitting to a nasogastric feeding tube that provided them with a nutritional slurry, the fat to carb ratio of which would induce ketosis.
Of course, the at-home, DIY version of keto isn't going to be as controlled as the one administered by a doctor in a hospital setting. The keto diet of yore was adjusted daily to reflect a human's fluctuating metabolism. "They had to measure everything that was coming into the body and what was coming out," says Nellis. So if you're not weighing your poop, you're not doing the hardcore keto diet. But there is a growing body of medical evidence advocating for an ad libitum (or as much as you feel like) ketogenic diet. The modern, self-administered keto diet relies on a fat-to-carbs ratio of 4:1. You can buy pre-ratioed like Ketocal, or freestyle your own diet. One health writer ate the same thing every day for a month to make sure she was on ratio. She liked not having to think about what to eat every day.
My friend gave herself a little more flexibility: "For breakfast I made a terrible smoothie with zero fruit, almond butter, almond milk, various seeds, and protein powder. For lunch everyday I would eat a bunch of vegetables, garbage meat like salami and a whole bunch of Brie. For dinner I usually had eggs or more trash meat." Bacon became a mainstay of her diet. It sounds counterintuitive—a health diet full of "trash meat." But there's some evidence that the keto diet can actually be good for your cholesterol. A 2004 study in Experimental & Clinical Cardiology found that LDL (bad cholesterol) decreased in obese patients who followed a keto diet for 24 weeks.
However, one study does not undo decades of nutritional science. A lot depends on the kind of fat you eat. Most keto diet websites advocate for "good" fats like avocado, coconut oil, butter, and medium chain triglycerides (MCT). MCT's are supposed to be broken down by the body more easily than other fats, which have longer triglyceride chains. But butter, coconut oil, and even the beloved MCT oil are saturated fats, which the Harvard School of Public Health still recommends should only account for 10 percent of your daily caloric intake.
There are definite risks to the keto diet. Besides keto breath, there's keto flu (flu-like symptoms associated with making the switch to ketosis) and keto rash. There are a few circulating theories on the mysterious cause of the rash: Some think it's a result of your gut flora reacting to the new diet, while others think the ketone bodies you sweat cause the irritation. Because the diet is so limited in what you can eat, getting enough vitamins and minerals is very difficult. Then there are more serious possible side effects like dysmenorrhea, kidney stones, and possibly even weakened bones. A buildup of ketones in the blood, called ketoacidosis, can be fatal.
"When the blood is this acidic, organs in the body aren't able to function properly," says Kayla Jaeckel, a dietician and diabetes counselor at Mount Sinai hospital."
But if you aren't diabetic, the chances of going into ketoacidosis are very slim. "A little bit of insulin is enough to keep the process under control," says Dr. Adrian Vella, an endocrinologist at the Mayo Clinic.
The long-term effects of a keto diet aren't well studied, partially because the attrition rate is so high. The keto diet relies on a person cutting all carbs from their diet—not just counting what's in one cup of brown rice. And there are hidden carbs and sugars in everything we eat: balsamic vinegar, starchy vegetables, store bought spaghetti sauce. "People usually go back," says Vella. Although the ketogenic diet isn't used to treat diabetes anymore, it's still an option for controlling epilepsy in children. One reason it's not used often for adults with epilepsy? They don't want to stick to the diet.
Gila gave up on her diet after eight months. "I was always sleepy and my shit floated," she says. "I felt drunk after eating a full dinner and dessert at my in laws. Disoriented." Whatever positives came from getting skinnier didn't outweigh the fear that she was doing serious damage to her body. "Keto was fun," she says. "Until it wasn't."
One last thing: a high fat diet can make your poop float. If you're going to try keto, invest in a multivitamin and a plunger.