Ketogenic Diet Shows Greater Impact on Liver Fat and Blood Sugar Control

A randomized clinical trial featured in Cell Metabolism has found that a ketogenic diet significantly reduced liver fat and improved blood sugar control more than Mediterranean or very-low-fat diets. Interestingly, participants across all three diets lost a similar amount of weight.

The study involved individuals dealing with obesity, prediabetes, and fatty liver disease. Those on the ketogenic diet saw their liver fat drop by an impressive 67%, while those following the Mediterranean or very-low-fat diets saw reductions of only 45%.

Notably, about half of the participants in the ketogenic group no longer met the criteria for prediabetes by the end of the study. This contrasts starkly with 29% in the Mediterranean diet group and just 7% in the low-fat group.

Professor Ziv Ben Ari, a leading liver specialist at the Center for Excellence in Liver Medicine in Israel, highlighted that these results are striking, particularly considering that weight loss was nearly identical across all groups.

He mentioned, “In a group of 55 individuals with obesity, prediabetes, and fatty liver, the ketogenic diet which led to about a 10% weight loss resulted in a 67% decrease in liver fat. This stands in comparison to a 45% reduction observed in those following a Mediterranean or very-low-fat diet.”

The ketogenic diet, commonly referred to as keto, significantly limits carbohydrate intake while emphasizing a higher percentage of calories from fats. This means cutting back on bread, pasta, rice, and most fruits, while meats, fish, eggs, avocados, olive oil, nuts, full-fat cheeses, and low-carb veggies are staples of the regimen.

This restriction pushes the body into ketosis, a metabolic state where it relies more on fat for energy and produces ketone bodies.

Fatty liver disease stems from the accumulation of fat in liver cells and is often tied to insulin resistance and metabolic syndrome. Ben Ari outlined that the condition is typically linked with obesity, diabetes, and elevated blood lipid levels.

While fatty liver is prevalent, only a smaller number of patients advance to more serious liver diseases. However, if left unchecked, it can result in cirrhosis and heighten risks of cardiovascular issues.

Addressing the condition usually combines lifestyle changes, weight management, and diet—like the Mediterranean approach—with some patients also needing medication.

A total of 55 participants underwent initial evaluations and were randomly assigned to one of three diets: a ketogenic diet, a Mediterranean diet, or a very-low-fat, plant-based diet. Ultimately, 42 individuals completed the study, averaging around 43 years old and with an initial average BMI of 38.9.

To maintain consistency, researchers provided all meals and snacks, requiring participants to consume only what was provided. Weekly meetings with a dietitian helped ensure adherence to the diets, which exceeded 95% across groups.

Caloric intake was personalized so participants would roughly lose 10% of their body weight. The outcomes were quite similar: a weight loss of 10.4% in the ketogenic group, 10.2% with the Mediterranean diet, and 10.1% in the very-low-fat group.

On average, it took about 4.6 months to reach targets on the ketogenic diet, compared to 5.4 months for Mediterranean and 5.1 months for low-fat. Researchers conducted thorough evaluations pre- and post-intervention, including blood tests, glucose tolerance tests, body composition assessments, and liver fat measurements obtained via specialized MRI techniques.

Each group lost both fat and lean mass, with fat loss comprising 71% to 75% of the total weight lost. Interestingly, muscle insulin sensitivity improved by about 50% across all groups, without significant differences between the diets.

However, the liver’s response was distinct. While liver insulin sensitivity improved in all diets, the ketogenic group displayed two to three times more improvement than the others and notably reduced new fat production in the liver.

The overall liver fat dropped by 67% in the ketogenic diet group, in contrast to the 45% reduction in the other diets. According to Ben Ari, a likely explanation could be reduced triglyceride accumulation in the liver.

Tracking liver fat levels using MRI methods allowed for precise measurements, which are crucial as excess liver fat can lead to inflammation and replacement of healthy tissue with scar tissue. Ben Ari emphasized that “scarred areas of the liver do not function.” As scarring progresses, the liver’s ability to perform its essential functions diminishes.

Additionally, blood glucose levels fell by 20% in the ketogenic group, against an 8% drop in the other diets, and insulin levels decreased by 74% on keto, compared to 44% and 27% reductions in the other groups.

Glucagon levels surged by 52% among those on the ketogenic diet while decreasing in others. Notably, beta-hydroxybutyrate, a key ketone body, increased more than twentyfold in the ketogenic group but remained unchanged in the Mediterranean group and dropped in the low-fat group.

Post-study, half of the participants on the ketogenic diet no longer fit the prediabetes criteria, a stark contrast to 29% on Mediterranean and 7% on the very-low-fat diet.

Furthermore, the ketogenic group saw greater declines in markers like fasting glucose and insulin levels. Yet, none of the diets enhanced pancreatic beta-cell function, indicating that prolonged carb restriction might not restore this function in prediabetic participants.

While fasting triglycerides fell across all groups, the greatest reduction was noted in the ketogenic group. Other factors including lipid particles and insulin resistance metrics also showed betterments in the keto group, although no significant differences appeared in overall cholesterol levels or blood pressure across the diets.

I suppose it’s quite interesting to note that the ketogenic diet in this study obtained 23% of its total calories from saturated fat, yet participants didn’t experience a spike in blood fat or cholesterol levels. This finding surprised Dr. Max Petersen, the study’s lead author.

No serious negative effects were reported, and no one dropped out due to side effects, which is always a good sign. Nevertheless, the researchers pointed out the limitations of the trial—its small size and relatively brief duration of four to five months. They cautioned that this study doesn’t clarify whether these benefits could last long-term, or if a less extreme carbohydrate restriction might yield similar results down the line.