The Keto Diet, Explained

It’s why people are putting grass-fed butter in their coffee, downing ketone drinks, and replacing their cereal and pasta with eggs and avocados.

The ketogenic diet has become a Silicon Valley obsession and the diet du jour that supposedly keeps celebrities like Kim Kardashian and Halle Berry trim and strong.

Keto devotees believe that if you banish most carbs (including fruit!) and embrace fat, you can lose weight without feeling hungry.

The diet’s long history in science also lends it credibility. Doctors have been prescribing ketogenic diets to treat epilepsy for nearly a century, and increasingly believe it may hold promise for people with Type 2 diabetes.

But what’s lost in the many trend articles and books about “going keto” for weight loss today is that this diet is the same one the now-late Dr. Robert Atkins and other low-carb evangelists have been selling since the 1960s. (Diet peddlers have an incredible knack for rebranding old ideas over and over, and in our eternal confusion about what to eat, we keep falling for it all.)

Those older keto diets didn’t work for most people hoping to slim down, and there’s no evidence the newly popular keto diet will be any different. Here’s why.
How the ketogenic diet works

To understand the ketogenic diet, you need a quick primer on how the human body gets energy. We are fueled primarily by glucose, or blood sugar, much of which we derive from carbohydrates in foods like bread, fruit, potatoes, and sweets.

If glucose levels in the blood drop to really low levels, we’d pass out and die. But, interestingly, the body can’t store much glucose — only enough to last a couple of days. So if we forgo eating carbs for a few days, we need other ways to keep going. One of those is a process called ketogenesis.

In ketogenesis, our livers start to break down fat into a usable energy source called ketone bodies, or ketones for short. “Organs like the brain that normally rely primarily on glucose for fuel can begin to use a substantial amount of ketones,” said Kevin Hall, a National Institutes of Health senior investigator who has studied the ketogenic diet. So ketones can stand in for glucose as fuel for the body when there’s a glucose shortage. “It’s an amazing physiological adaption to starvation that allows tissues like the brain to survive,” Hall added.

Once ketogenesis kicks in and ketone levels are elevated, the body is in a state called “ketosis,” where you’re burning stored fat. There are a few ways to get into ketosis. One is through fasting: When you stop eating altogether for an extended period of time, the body will ramp up fat burning for fuel and decrease its use of glucose (which is part of the reason people can survive for as long as 73 days without food).