Low-carb diet improves metabolic syndrome in some cases

A low-carb diet may have benefits for people at risk of developing type 2 diabetes even if they don't lose any weight, according to a new study by researchers at Ohio State University in Columbus and published in the Journal of Clinical Investigation Insight.

Researchers wanted to know what happens to obese people with metabolic syndrome, a precursor to diabetes, when they eat a diet low in carbohydrates but don't lose weight. They found that more than half of study participants no longer met the criteria for metabolic syndrome immediately following a four-week low-carb diet.

In the study, which was supported by the National Dairy Council and the Dutch Dairy Association, the research ream looked at 16 men and women with metabolic syndrome, a cluster of factors that also put people at higher risk of heart disease and stroke. Over about four months, each study participant ate three month-long controlled diets, high-carb, moderate-carb, and low-carb, with a two-week break between diets. The diets intentionally contained enough calories to keep participants’ weight stable. The order in which the participants ate the diets was randomly assigned.

After eating a low-carb diet, more than half the participants, five men and four women, saw their metabolic syndrome reversed, even though their caloric intake equaled their energy expenditure and they did not lose weight, according to Parker Hyde, PhD, lead researcher in the study.

Additionally, participants had a variety of significantly improved health measures, particularly lower triglycerides and improved cholesterol readings. Despite the fact that the low-carb diet contained 2.5 times more saturated fat than the high-carb diet, it decreased saturated fat in the bloodstream and was associated with an increase in the size of cholesterol particles in the blood, which decreases the risk of cardiovascular disease, Hyde said.

The researchers also report evidence of increased fat-burning efficiency after a low-carb diet and an improvement in blood sugar. They did not see statistically significant improvements in blood pressure or insulin resistance.

Three participants no longer had metabolic syndrome after the moderate-carbohydrate diet and one no longer had the syndrome after the high-carb diet. Jeff Volek, PhD, RD, the study's senior author and a professor of human sciences at Ohio State University, said that the results are likely explained by the fact that even these study diets, particularly the moderate-carb diet, represented a shift toward fewer carbs for study participants.

The conditions that contribute to metabolic syndrome include high blood pressure, high blood sugar, excess body fat around the waist, and abnormally low High-density lipoprotein cholesterol or high triglyceride levels. About a third of American adults have the syndrome, according to the American Heart Association.

Previous research has shown that low-carb diets can be beneficial for people with metabolic syndrome and diabetes, but nutrition scientists and others have debated whether that's a product of the diet or a product of the weight loss typically seen when people reduce carbs, according to Volek.

Because of the study design, waist circumference was not factored in as a contributor to metabolic syndrome. Had the participants been permitted to lose weight, it is likely that several more would have been considered free of the condition after the low-carb diet, Volek said.

This research doesn't address the potential long-term benefits and challenges of adopting a low-carbohydrate diet, and the researchers suggest that future long-term diet studies on people with metabolic syndrome need to include low-carb diets.

“There's no doubt that people with metabolic syndrome and type 2 diabetes do better on low-carb diets, but they typically lose weight and one of the prevailing thoughts is that the weight loss is driving the improvements,” Volek said in a statement. “That was clearly not the case here. Our view is that restricting carbs even without weight loss improves a host of metabolic problems. Obviously, quality of diet matters because quantity is locked down in this experiment."