The Ketogenic Diet
What it is: Our body traditionally uses glucose to fuel both our muscles and our brain. When you cut your carb intake to less than 10 percent of your total calories (less than 5 percent for die-hards), the glucose deprivation forces your body to instead use fat as fuel in your workouts, and forces your brain to release ketones, a unique backup brain food that has side effects like stopping epilepsy and unbelievable mental clarity.
What the research says: In the short term, the keto diet is pretty safe and effective. Research on overweight folks has found cutting carbs and increasing fat consumption can shed excess weight, improve insulin resistance, reduce blood pressure, improve cholesterol levels, and maybe even offset type 2 diabetes risk. And it’s probably an improvement over how most Americans eat: A 2017 study in Diabetes & Metabolic Syndrome reports that for overweight and obese people, going keto and not exercising may be a healthier option, metabolically and aesthetically, than eating the standard American diet and working out three to five days a week.
But it might not be superior to other healthy diets. When overweight or obese men spent four weeks eating either keto or a healthy, high-carb diet, they burned more calories on a daily basis without the macro—but it actually took them a full month to lose the same amount of body fat on a keto diet as they lost in two weeks on the high-carb diet, according to the results published in the American Journal of Clinical Nutrition. And when it comes to healthy dudes, most research shows keto is just as effective as any other diet at reducing fat, but it compromises anaerobic, aerobic, and strength performance when you’re relying on fat as fuel rather than carbs.
And science doesn’t support eating this way long term: A recent study in The Lancet suggests limiting your carb intake in the long term can shorten your lifespan, probably because you’re cutting your fruit and vegetable intake, while another large study presented at the 2018 European Society of Cardiology Congress found people on the lowest-carb diets were the most likely to die from cancer, cardiovascular disease, and all other causes.
The pros: In the short term, going keto can help you get lean while retaining muscle and, because you’re consuming so much fat, you won’t be as hungry as you might be if you were restricting calories, says White. Plus, you’re cutting unhealthy carbs like donuts and pastries and you’re getting more nutrients than the carnivore diet since you’re eating at least some fruits and vegetables.
The Cons: You’ve got to count your calories, since fat has more than double the calories of protein or carbohydrates, gram for gram. And you might be more constipated and bloated—less plants means less fiber, which is crucial to support digestive function. This is compounded by high intake of hard-to-digest protein intake, White says.
The real risk, though, comes from where your fat sources come from. Since most plants are high in carbs, you’ll likely end up eating a lot of animal products which are high in saturated fat and bad cholesterol, increasing your risk of heart disease, White points out. But as keto becomes more popular, so do variations that might help offset the risks of the higher disease in the long term, like the keto-mediet which has you replace red meat and dairy with healthier, medium-chain fatty acids in coconut oil, or the newly released ketotarian diet, which is all about marrying keto with vegetarianism.
Who it’s best for: In the short term, it may be an effective and safe option for cutting, when you want to decrease fat without losing lean mass—but it’ll work against you when you’re trying to bulk. And for most athletes—especially endurance athletes—the body comp payoff of keto isn’t enough to justify how a low-carb plan will compromise your performance, White says.