Doubling and even nearly tripling saturated fat in diets does not drive up total levels of saturated fat in the blood, according to a controlled diet study.
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 carbohydrates were reduced. Palmitoleic 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 re-introduced to the study diet.
However, 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.
In the study, participants were fed six three-week diets that progressively increased carbohydrates while simultaneously reducing total fat and saturated fat, keeping calories and protein the same.
A sampling of foods provided to research participants during the three weeks that they were eating a very-low-carb diet. Credit: Ohio State University
The finding “challenges the conventional wisdom that has demonized saturated fat and extends our knowledge of why dietary saturated fat doesn’t correlate with disease,” said senior author of the PLOS One paper Jeff Volek, a professor of human sciences at The Ohio State University. “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.”
When that marker increases, he said, it is a signal that an increasing proportion of carbs are 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 won’t be stored.
“When you consume a very low-carb diet your body preferentially burns saturated fat,” Volek said. “We had people eat 2 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.”