Diet high in carbs, not fat, linked to disease.

• Position: Saturated Fat - Diabetes and heart disease

Doubling or even nearly tripling saturated fat in the diet does not drive up total levels of saturated fat in the blood, according to a controlled diet study by Jeff Volek, professor of human sciences at Ohio State University, Columbus. Plowever, increasing levels of carbohydrates in the diet during the study promoted a steady increase in the blood of a fatty acid linked to an elevated risk for diabetes and heart disease.

The finding "challenges the conventional wisdom that has demonized saturated fat and extends our knowledge of why dietary saturated fat does not correlate with disease," says Volek.

In the study, participants were fed six three-week diets that progressively increased carbs while simultaneously reducing total fat and saturated fat, keeping calories and protein the same. The researchers found that total saturated fat in the blood did not increase--and went down in most people--despite being increased in the diet when carbs were reduced. Palmltoleic acid, a fatty acid associated with unhealthy metabolism of carbohydrates that can promote disease, went down with low-carb intake and gradually increased as carbs were reintroduced to the study diet.

"It's unusual for a marker to track so closely with carbohydrate intake, making this a unique and clinically significant finding. As you increase carbs, this marker predictably goes up," Volek indicates.

When that marker increases, it is a signal that an increasing proportion of carbs is being converted to fat instead of being burned as fuel. Reducing carbs and adding fat to the diet in a well-formulated way, on the other hand, ensures the body will promptly burn the saturated fat as fuel--so it will not be stored.

"When you consume a very low-carb diet your body preferentially burns saturated fat," Volek explains. 'We had people eat two times more saturated fat than they had been eating before entering the study, yet when we measured saturated fat in their blood, it went down in the majority of people. Other traditional risk markers improved, as well."

Volek and colleagues recruited 16 adults for the study, all of whom had metabolic syndrome, defined as the presence of at least three of five factors that increase the risk for heart disease and diabetes (excess belly fat, elevated blood pressure, low "good" cholesterol, insulin resistance or glucose intolerance, and high triglycerides).

After getting them to a baseline reduced-carb diet for three weeks, researchers fed the...