11.09.2015
Study suggests liver fat is the driver

by Parker Brown
Staff Writer, MedPage Today

LOS ANGELES — Restricting sugar led to improved insulin sensitivity in a small trial, pointing to the role of fructose on metabolic syndrome, researchers said here.

The research — presented during a poster session here at the annual Obesity Week — was the second report from a study conducted in the lab of prominent sugar and processed-foods researcher Robert Lustig, MD, from the University of California San Francisco. The first, published recently in the journal Obesity, reported that when 43 children with obesity cut their dietary sugar from 28% to 10% of their diet and replaced it with starches, their metabolic parameters improved significantly after 9 days.

The presentation here was an attempt to explain the mechanism behind the usual trajectory of worsening metabolic profiles, said Lustig in an interview with MedPage Today.

Children in the trial had lost a substantial amount of hepatic fat (22%) and visceral fat (7.3%), but not subcutaneous fat; and fasting insulin, initial area under the curve (IAUC), c-peptide, and Composite Insulin Sensitivity Index (CISI) improved.

Twenty-two of the patients had liver steatosis of greater than 5% at baseline; all of them lost liver fat and had their insulin sensitivity improve. The question that the researchers then tried to answer was whether the loss in liver fat correlated with improved insulin sensitivity, said Lustig.

They found that the improved insulin sensitivity was due to changes in liver fat, and not changes in the visceral fat. “The visceral fat played no role,” Lustig added. “This says that we can fix obese children’s metabolic health in 9 days on the same number of calories, without changing subcutaneous fat,” he said.

The first study established that the changes in liver fat were due to fructose. “And now we know the liver fat predicts the changes in insulin sensitivity,” said Lustig.

The earlier study received significantattention, but the small size of the study left it open to criticism that it was underpowered. But Lustig said that the study was generally well-received among researchers.

Patients were either Hispanic or African-American and all were ages 9 to 18. All of them consumed copious amounts of sugar — at least 50 grams per day — and had evidence of at least one comorbidity. The researchers attempted to keep weight constant, which meant that they had to increase portions, said Lustig.

Patients were weighed daily and the calories were adjusted. All the investigators were blinded to all the data until the study was over. Glucose tolerance tests were performed. The pre-study diets of the children were used as a control, and researchers attempted to keep other factors besides sugar consumption consistent.

“We needed to isolate sugar, and the only way to do that was to provide them with as crappy of food as they started with,” said Lustig, adding that the findings have “enormous public health implications”.

“These data support the assertion that fructose restriction should be an integral modality to improve metabolic status in children with obesity, irrespective of weight loss,” concluded the researchers.