Study Explains Why Keto Diet Leads to Weight Loss

A ketogenic diet helps with weight loss by reducing caloric intake, not by promoting calorie burning, according to a new study.

About 7% of Americans followed a ketogenic diet in 2022, which is low in carbohydrates and rich in fat. The eating pattern is touted for weight loss benefits, although experts warn that it lacks fiber and increases the intake of saturated fats.

Previous research has suggested that the keto diet may induce weight loss by promoting energy expenditure, or the amount of energy the human body burns.

A new study in Cell Reports Medicine examined the diet’s effects on physical activity energy expenditure, which is the energy above rest expended during body movement and postures.

The study included 53 healthy adults without obesity, about one-third of whom were assigned to a keto diet, in which less than 8% of daily calories came from carbohydrates.

Another third of participants followed a diet restricting free sugars — added sugars found in cakes, sweets, and some fizzy drinks — to less than 5% of the total caloric intake. Eighteen participants were randomized to a control diet, where sugar and carbohydrate content accounted for about 18% of all caloric intake.

After 12 weeks, diets restricting free sugars and carbohydrates did not meaningfully alter physical activity or other components of energy expenditure.

However, as these diets reduced caloric intake, they altered body composition. On average, participants on the keto diet lost about 1.6 kg of fat, compared to about 1 kg on other diets.

The authors note that diets restricting carbohydrates tend to be less palatable, resulting in consuming fewer calories.

At week four, sugar restrictions reduced total cholesterol concentrations. Meanwhile, individuals on the keto diet had 16% higher levels of LDL cholesterol, also known as “the bad” cholesterol.

Those eating the keto diet also had 26% higher levels of a protein called apolipoprotein B, linked to an elevated risk of heart disease.

Additionally, the ketogenic diet lowered the abundance of Bifidobacterium, a healthy type of bacteria in the gut commonly used as probiotics. The reduction may be linked to decreased fiber intake, which supports the survival and activity of organisms in the intestines.

The study concludes people on a keto diet lose weight not because it promotes energy expenditure, but because they consume fewer calories.