Do the pros of the ketogenic diet outweigh the cons? For me, they don’t. Here's why.
Long-time listeners of the Nutrition Diva podcast might recall an episode I did in 2013 in which I briefly mentioned the ketogenic diet. I didn’t get into too many details about the diet; I was talking about how two people can get similar results following diametrically opposed strategies. (Also, about the extremes that some people go to in order to lose weight!)
As I said back then, the ketogenic diet deserves an episode of its own. In the five years it’s taken me to make good on that promise, the ketogenic diet has gone from a fringe fad diet to a mainstream fad diet! Every week, I get questions from listeners about what this diet is, whether it’s effective, and whether it’s safe.
Not that you have to ask me to get answers to these questions! I’m sure that there are several people in your office, at your gym, in your carpool, and around your Thanksgiving table that can give you their opinion, based on personal experience or stuff they read on the internet. But here, better late than never, is a perspective based on the evidence—such as it is.
What's the Evidence for the Ketogenic Diet?
One of the reasons it has taken me so long to venture into this topic more fully is that the evidence on the ketogenic diet for weight loss has been pretty skimpy.
This diet has been very well-researched as a therapy for epilepsy. Although it can be very effective in preventing seizures, it is usually conducted under strict medical supervision. And not just because epilepsy is a serious condition. Until more recently, the ketogenic diet was considered far too extreme and potentially risky to recommend for general use.
Now, it is one of the fastest growing diet and weight loss trends, touted in best-selling diet books and by celebrities, personal trainers, and other people that you might not necessarily want to take medical advice from.
What Is a Ketogenic Diet?
Since the ketogenic diet has become so popular, the meaning of the term has also become somewhat diluted. Many people say they are "eating keto" because they choose “keto-friendly” snack foods or energy bars, or take the top bun off their burgers. A true ketogenic diet is extremely low in carbohydrates, usually less than 50 grams per day, or about 10% of calories. (The typical diet contains four to five times that much.)
The idea is to eat so few carbs that it forces your body into a state of ketosis. Instead of using glucose from your food or glycogen from your muscle to fuel biological processes, your body will turn fat into an alternate source of energy called ketones. For those tissues and organs that can’t utilize ketones, the body also has a way of turning amino acids from protein into glucose.
One thing that people like about ketogenic diets is that, as long as you strictly restrict your carb intake, you can eat as much as you want! If all of this sounds familiar it's because most of us first learned about ketosis when the Atkin's diet became popular back in the 70s. Unlike the traditional Atkin’s style low-carb diet, which was pretty high in protein, today’s ketogenic diets tend to be much higher in fat, up to 80% of calories.
Is the Ketogenic Diet Effective for Weight Loss?
You will probably lose weight on a ketogenic diet, despite being able to eat as much as you want. Contrary to what you read online, however, very little of this has to do with the metabolic "magic" of ketosis. Converting fat into ketones and protein into glucose does burn up a little more energy than burning carbs for fuel. But this ends up being a very small factor. The main reason that people lose weight on ketogenic diets is that they simply take in fewer calories.
Being in ketosis has a rather profound appetite-suppressing effect. Anything that suppresses your appetite is obviously going to make it easier to limit your calorie intake. Another reason that people take in fewer calories is that a very high fat diet—as fun as that might sound—is not necessarily very appetizing.
True: You’ll lose weight quickly
Weight loss on a ketogenic diet is likely to be fairly rapid, especially at first. But much of that initial weight loss is water. Being in ketosis is very dehydrating and can even lead to electrolyte imbalance. (This is why this diet used to only be done under medical supervision.)
False: You'll lose more fat
Although a ketogenic diet does force your body to burn fat for fuel, research finds that this does not translate into losing more body fat. In studies that have compared the ketogenic diet to other diets, total weight loss and fat loss was not significantly different. In some studies, lean tissue loss was greater on ketogenic diets than on other diets. If you are on a ketogenic diet, you can mitigate some of the muscle loss with strength training. (And for tips on that, check out the Get Fit Guy podcast.)
The truth is that rapid weight loss sets the stage for weight regain, by increasing lean muscle loss and decreasing your metabolic rate. That’s why I am always making the case for slow weight loss.