THE “KETO” DIET MIGHT seem like the newest thing to hit the weight-loss scene since sliced (whole-grain) bread. But it has actually been around for nearly a century – as a treatment for epilepsy.
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Physicians first introduced the high-fat, low-carb eating approach in the 1920s after discovering that prolonged fasting (in which the body is forced to run off of its fat stores) reduced the frequency and intensity of seizures in epileptic patients, explains Dominic D’Agostino, an associate professor at the University of South Florida Morsani College of Medicine, who began studying ketogenic diets a decade ago as a way for the U.S. Navy to prevent seizures in underwater divers. While scientists still aren’t sure exactly how the keto diet helps manage seizures, it may have other benefits, too, he says. The most popular purported perk: weight loss.
By following an extremely low-carb, high-fat diet, the body enters a state of ketosis. The liver converts fat into fatty acids and ketones, compounds the body can use for energy when it can’t rely on carbs, says Eric C. Westman, director of the Duke Lifestyle Medicine Clinic. This fat includes body fat as well as dietary fat. (Hence the chorus of celebrity declarations that the diet has uncovered long-dormant abs.)
What’s more, ketones may send satiety signals to the brain, says Donald K. Layman, professor emeritus of food science and human nutrition at the University of Illinois–Urbana-Champaign. However, for ketone levels to be high enough to confer their purported weight-loss benefits, daily carb intake must be cut to about the amount in a single apple. (You read that right.) “The ketogenic diet is extremely restrictive and not sustainable for everyone,” Layman says. D’Agostino adds that the original ketogenic diet required getting 85 to 90 percent of one’s daily caloric intake from fat, 8 to 10 percent from protein, and as close to zero percent from carbs as possible. Current approaches have generally increased protein to about 100 to 120 grams or 20 to 30 percent of calories, but higher levels can hinder ketosis.
Ensuring ketosis involves diligent tracking of calories and macronutrients, and some followers opt to measure ketone levels with urine test strips. Because ketosis can influence how the body reacts to certain medications, anyone considering the diet should consult their doctor first, experts say. Also, without supervision by a registered dietitian, nutritional deficiencies are a real risk. Low energy levels and brain fog are common as the body adapts to using ketones for energy, and experts disagree over whether the body can perform optimally, especially during high-intensity exercise, when running on ketones. A panel of experts tied the diet in last place in U.S. News’ 2018 Best Diets rankings (page 84), expressing concern over its emphasis on high-fat foods. Said one panelist: “This diet is fundamentally at odds with everything we know about long-term health.”
Layman’s research suggests the ketogenic diet is no more effective at spurring weight loss than similar-calorie diets that restrict daily carbs to less than 140 grams. He notes that the average American’s consumption of carbohydrates, at roughly 300 grams per day, is more than double what the National Academy of Sciences states is consistent with good nutrition. And most of these carbs come from ultra-processed foods – think frozen pizza and soda – and added sugar. So, yeah, if you swear off carbs, you’ll likely eat far fewer calories, he says. The result: You’ll lose weight.