On Nutrition

Originally developed to treat severe epilepsy in infants and children, today the ketogenic diet has gone mainstream — but not without controversy.

The ketogenic diet isn’t just any low-carbohydrate diet. It’s very low in carbohydrates and very high in fat, putting the body into ketosis, a state where it burns fat instead of glucose (sugar) for fuel. But while research has demonstrated some short-term benefits, research on long-term effects — both positive and negative — of the ketogenic diet is currently lacking.

Diets labeled as “ketogenic” vary widely, but the true ketogenic diet can have a ratio of 75% to 85% calories from fat, 10% from protein and as little as 5% from carbs. That often means 20 to 50 grams of carbs per day, primarily from nonstarchy vegetables like salad greens and broccoli. Because protein can be converted to glucose, it’s kept high enough to reduce the risk of muscle loss but low enough to prevent nudging the body out of ketosis.

Many people think they are following a ketogenic diet, but they’re really just eating low-carb, which means they aren’t in ketosis. One reason I often hear: “I just can’t eat that much fat.” Or, they take “breaks” from doing keto on the weekends. But researchers I’ve asked about this say that going in and out of ketosis is not a good idea. Many people don’t want to measure ketones using a finger stick device, but peeing on a urine strip isn’t a good measure of ketones in the blood, because it’s normal to produce some ketones after not eating for a while — it doesn’t mean we’re in ketosis.

The ketogenic diet is popular because it works when followed correctly, at least in the short term (there are no studies showing whether it makes people more likely to keep weight off long term). So why does it work for many people in the short term? It’s possible that reduced dietary variety leads to reduced calorie intake — especially for people who don’t enjoy eating that way. Reduction in appetite is said to be another reason, although new research questions that.

Study results published last month in the journal Nature Medicine by researcher Kevin Hall and colleagues from the National Institutes of Health found that study participants needed more calories to satisfy hunger when following a ketogenic diet than they did when following a plant-based, low-fat diet. They lost more muscle while following the ketogenic diet and more fat while following the low-fat diet, even though this was not a weight loss study. The study did show that the keto diet was better for reducing blood sugar and insulin, which is consistent with previous studies. What research has not demonstrated in humans is that it reduces risk of the things we really care about — heart attacks, heart disease and Type 2 diabetes — or helps us live longer.

Here’s some more food for thought: ketogenic diets don’t just eliminate sugar and refined carbohydrates — they also curtail pulses, whole grains, fruit and starchy vegetables. All of these foods contribute vitamins, minerals, antioxidants, phytochemicals and fiber — including prebiotic fiber that promotes a healthy gut microbiota. The restrictive nature of the diet could trigger disordered eating or even eating disorders in susceptible people.

Finally, just because the ketogenic diet is trendy doesn’t mean it’s magic or even special. There are other dietary patterns that can help us be healthier, including lower-carb, lower-fat, and all points in between.