Researchers compared three diets in 55 adults with obesity. All also had prediabetes and excessive fat accumulation in the liver. For about five months, each participant received all of their meals, making it possible to precisely control their diet.
One group followed a ketogenic diet, very low in carbohydrates and high in fat. Another ate according to a Mediterranean diet. The third followed a mostly plant-based diet, high in carbohydrates and very low in fat. In all three groups, weight loss reached about 10% of initial body weight.
Salmon, meat, eggs, vegetables and avocado.
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This weight loss had already produced an important effect shared by all groups. The muscles responded about 50% better to insulin, the hormone that helps glucose enter cells. On this point, the composition of the meals made no notable difference.
The liver reacted differently. Among participants following the ketogenic diet, its sensitivity to insulin improved two to three times more. The amount of fat stored in this organ decreased by 67%, compared with about 45% with each of the other two diets.
To understand the significance of this difference, the liver plays a major role in regulating blood sugar. When it responds poorly to insulin, it may continue releasing too much glucose into the bloodstream. Fat accumulation in this organ frequently accompanies this dysfunction in people with obesity.
Measurements taken over 24 hours point in the same direction. Average blood glucose fell by 20% with the ketogenic diet, compared with about 8% with the other two. Insulin concentrations also decreased more substantially. After the intervention, half of the participants in this group no longer met the criteria for prediabetes, compared with 29% with the Mediterranean diet and 7% with the low-fat plant-based diet.
One might think that a diet high in fat inevitably increases the amount of fat circulating in the blood. Yet the researchers found no difference between the groups in LDL cholesterol, apolipoprotein B or triglycerides measured over 24 hours. However, these results come from a small, tightly controlled study involving a specific population.
It remains to be understood why such a sharp reduction in carbohydrates produces these additional effects on the liver. The researchers now want to study the mechanisms responsible for the metabolic benefits of weight loss, particularly when it is achieved with drugs that act on GLP-1.