Keto Diet Study Finds 67% Liver-Fat Reduction
A new keto diet study has found that three popular eating plans produced roughly the same amount of weight loss, but one delivered significantly greater improvements in liver fat, blood sugar and insulin levels.
The randomized clinical trial, led by researchers at Washington University School of Medicine in St. Louis, compared a very-low-carbohydrate ketogenic diet with a Mediterranean diet and a high-carbohydrate, low-fat plant-forward diet.
After about five months, participants in all three groups lost approximately 10% of their starting body weight. However, the ketogenic group experienced a substantially larger reduction in liver fat, with levels falling by 67%, compared with 45% in the other two groups.
The findings, published August 27 in the peer-reviewed journal Cell Metabolism, could add a new dimension to the long-running debate over whether the best diet is simply the one that produces weight loss or whether the composition of the diet matters as well.
The researchers stressed, however, that the results apply specifically to adults with obesity, prediabetes and excess liver fat. They do not establish that a ketogenic diet is universally superior for everyone seeking to lose weight.
Keto Diet Study Compared Three Popular Eating Plans
The study involved 55 adults with what researchers described as metabolically unhealthy obesity. Participants had obesity along with prediabetes and fatty liver.
Researchers randomly assigned them to one of three dietary patterns for approximately five months.
The first group followed a low-carbohydrate, high-fat ketogenic diet. The second followed a Mediterranean diet containing a more balanced mixture of carbohydrates and fats. The third followed a high-carbohydrate, low-fat plant-forward diet.
One of the study’s most important features was how closely researchers controlled what participants ate.
Participants received 100% of their food from the study team and met weekly with a dietitian. That gave researchers unusually detailed control over the participants’ diets and reduced uncertainty about whether people were actually following their assigned plans.
That distinction matters because nutrition studies often depend on participants accurately remembering and reporting what they eat.
In this trial, researchers had far more confidence that differences in metabolic outcomes were related to the dietary patterns being studied.
All Three Diets Produced Similar Weight Loss
The headline finding may seem surprising.
Despite their major differences in carbohydrate, fat and protein composition, all three diets produced approximately the same amount of weight loss.
Participants lost about 10% of their initial body weight over the study period.
They also experienced an approximately 50% improvement in insulin sensitivity in their muscles. Researchers said the similar improvements suggested that weight loss itself was a major driver of the improvement in muscle insulin resistance rather than the specific ratio of carbohydrates and fats in the diet.
That finding challenges the idea that one particular diet must always be superior for weight reduction.
Instead, it suggests that several very different approaches can produce meaningful weight loss when people follow them consistently.
The more interesting differences appeared when researchers looked beyond the scale.
Keto Diet Study Reveals Major Difference in Liver Fat
The biggest contrast emerged in liver health.
Participants following the ketogenic diet reduced the amount of fat stored in their liver by 67% after five months. The other two groups experienced a 45% reduction.
The researchers also found that insulin sensitivity in liver cells improved two to three times more among people following the ketogenic diet than among those following the other plans.
The liver plays a central role in regulating blood glucose. When liver cells respond appropriately to insulin, the liver can better control how much glucose it releases into the bloodstream.
That makes the finding particularly important for people who already have problems with blood sugar regulation.
The results do not mean that every person with fatty liver should automatically switch to a ketogenic diet. Rather, they suggest that the composition of a weight-loss diet may influence certain metabolic outcomes beyond the amount of weight lost.
Blood Sugar Improved More on the Ketogenic Diet
The differences were not limited to liver fat.
The ketogenic diet also produced greater improvements in blood sugar control.
Researchers measured participants’ glucose levels over a 24-hour period. Those following the ketogenic plan experienced a 20% reduction from baseline, compared with an 8% reduction among participants on the other two diets.
Daily insulin levels also fell substantially.
The ketogenic group experienced a 74% decrease in daily insulin levels. The Mediterranean group recorded a 44% reduction, while the high-carbohydrate group experienced a 27% reduction.
Researchers explained that the sharp decline in insulin levels on the very-low-carbohydrate diet partly reflects the reduced need for insulin when carbohydrate intake is dramatically restricted.
The findings suggest that two diets can produce similar weight loss while affecting glucose and insulin metabolism differently.
Prediabetes Reversal Was Also Higher in the Keto Group
Another notable finding involved prediabetes.
Half of the participants assigned to the low-carbohydrate ketogenic diet no longer met the study’s criteria for prediabetes by the end of the trial.
That compared with 29% of participants in the Mediterranean diet group and 7% of those following the high-carbohydrate, low-fat plant-forward diet.
Those numbers are striking, but they should be interpreted carefully.
The study included only 55 people, meaning each diet group was relatively small. A larger trial would be needed to determine how reliably the differences would appear in a broader population.
The study also lasted only about five months.
That means the researchers were able to document meaningful short-term metabolic changes, but the trial cannot establish whether the differences would remain over several years or whether they would translate into fewer cases of diabetes, cardiovascular disease or advanced liver disease.
Why Liver Fat Matters
Fat accumulation in the liver is increasingly recognized as an important metabolic health concern.
Excess liver fat can occur alongside obesity, insulin resistance and prediabetes. Over time, metabolic problems can contribute to more serious disease.
The WashU researchers noted that fatty liver disease affects a large proportion of adults with obesity worldwide and has become a major contributor to chronic liver disease and cirrhosis.
That makes the 67% reduction seen in the ketogenic group particularly interesting.
The result suggests that losing weight is not necessarily the entire story.
Two people could lose a similar percentage of their body weight while experiencing different changes in where fat is stored and how their organs respond to insulin.
For researchers, that raises a larger question: Could the composition of a diet influence metabolic health independently of weight loss?
This trial suggests the answer may be yes, at least for some outcomes in a specific group of patients.
The Study Does Not Prove Keto Is Best for Everyone
Despite the dramatic numbers, researchers were careful about the limits of their conclusions.
The participants were not a random sample of the general population.
They were adults with obesity, prediabetes and excess liver fat. That is a specific metabolic profile, and the results cannot automatically be applied to people who do not have those conditions.
The trial also tested highly controlled diets.
Participants received all of their food from researchers and received ongoing dietary support. In ordinary life, maintaining a strict ketogenic diet—or any highly structured eating plan—can be considerably more difficult.
That is why the researchers continue to emphasize the importance of diet adherence.
A theoretically effective diet may have limited real-world value if a person cannot maintain it.
At the same time, the findings indicate that adherence is not the only consideration. Once people successfully followed the assigned diets and lost similar amounts of weight, the ketogenic plan still produced different results for several metabolic measures.
Mediterranean and Plant-Forward Diets Still Delivered Benefits
The results should not be interpreted as showing that the Mediterranean and plant-forward diets failed.
They did not.
Participants following all three dietary approaches lost substantial amounts of weight and improved muscle insulin sensitivity. Both of the non-keto groups also experienced reductions in liver fat and improvements in metabolic health.
The key difference was the magnitude of certain improvements.
That distinction is important because the study was not a simple comparison between a successful diet and two unsuccessful ones.
Instead, researchers compared three diets that all produced meaningful weight loss and then examined whether the metabolic effects were identical.
They were not.
The ketogenic diet appeared to offer additional benefits for liver insulin sensitivity, liver fat, glucose control and circulating insulin levels in this particular group.
What Makes the Findings Different From Typical Diet Research?
Nutrition research is notoriously difficult.
People eat different foods, portion sizes vary, and participants may not follow instructions perfectly. Researchers therefore often have trouble determining whether an observed health effect comes from a diet itself, the amount of weight lost, or differences in adherence.
The WashU trial attempted to address that problem by supplying all of the participants’ food.
Researchers could therefore control the nutritional composition of each diet much more precisely.
The participants also met weekly with dietitians, helping maintain adherence throughout the trial.
That design gives the findings additional value.
It does not eliminate every limitation, but it makes the comparison between the diets more controlled than many real-world diet studies.
The Bigger Lesson May Be About Metabolic Health
The study’s most important message may not be that everyone should follow a ketogenic diet.
Instead, it may be that weight loss and metabolic health should be viewed as related but separate outcomes.
Weight loss itself produced major benefits across all three groups.
However, once researchers examined liver insulin sensitivity, liver fat, glucose levels and insulin concentrations, the diets began to separate.
That suggests that the question “Which diet helps people lose the most weight?” may be too narrow.
For people with metabolic disease, a more useful question may be: “Which dietary pattern produces the health changes that matter most for that individual?”
The answer could differ depending on a person’s health status, preferences, ability to adhere to a diet and medical needs.
Researchers Want to Understand Why Keto Performed Differently
The study also opens the door to additional research.
Scientists want to understand the biological mechanisms behind the different metabolic responses.
The WashU team said future studies will examine how weight loss produces these metabolic improvements and will also investigate the role of GLP-1 medications.
That is increasingly relevant as GLP-1 drugs become an important part of obesity treatment.
Some people use medication to help achieve weight loss, while others rely on dietary and lifestyle changes. Understanding how these approaches affect liver fat, insulin sensitivity and glucose metabolism could help researchers develop more targeted strategies in the future.
The new trial provides a useful starting point because it separates the effect of weight loss from some of the metabolic effects associated with dietary composition.
What the Keto Diet Study Means for Weight Loss
The findings offer a nuanced answer to the debate over which popular diet is best.
If the goal is simply weight loss, the three diets performed similarly in this controlled trial.
If the goal is improving certain metabolic markers in adults with obesity, prediabetes and fatty liver, the ketogenic diet produced additional benefits.
Most notably, liver fat fell 67% in the ketogenic group compared with 45% in the Mediterranean and plant-forward groups. Liver insulin sensitivity also improved more substantially, while blood glucose and daily insulin levels fell further.
But the study does not establish that keto is universally the healthiest diet.
It was a relatively small, short-term trial involving a very specific population. More research is needed to determine whether the results persist over longer periods and whether similar benefits occur in other groups.
For now, the strongest conclusion is more measured.
Weight loss itself appears to provide broad metabolic benefits, regardless of whether it comes from a ketogenic, Mediterranean or plant-forward approach. Yet the new evidence suggests that diet composition may still matter when the goal extends beyond the number on the scale.
For people dealing with obesity, prediabetes or fatty liver disease, those differences could become an important area of future nutrition research.
