New research links diet high in carbs — not fat — to diabetes, heart disease risks
By Michael Fielding on 12/5/2014
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. 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.
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,” senior author Jeff Volek, a professor of human sciences at The Ohio State University, said in a news release. “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.”
The researchers found that total saturated fat in the blood did not increase — and actually dropped in most people — despite being increased in the diet when carbs 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.
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.
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 won’t be stored.
“When you consume a very low-carb diet your body preferentially burns saturated fat,” Volek said. “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.”
The study does not address what happens to palmitoleic acid levels when high carbs are combined with a diet high in saturated fat. Instead, Volek hoped to identify the carb-intake point at which participants began to store fat.
“That turned out to be highly variable,” he said. “Everyone showed increased palmitoleic acid levels as carbs increased, but values varied widely between individuals, especially at the highest carb intake. This is consistent with the idea that people vary widely in their tolerance to carbohydrates.”
Participants’ existing health risks were not a factor in the study because everyone ate the exact same diet for 18 weeks. Their bodies’ responses to the food were the focus of the work.
Fat is the new black
U.S. consumers increasingly are demanding their beef, even as higher prices normally would have dampened sales and consumption.
And what seems to be fueling the demand is a wave of media coverage, first, of the results of a meta-analysis of existing health data, released in March 2014, that questions the longstanding link between saturated fat and heart disease; and second, the April release of the book, “The Big, Fat Surprise: Why butter, meat and cheese belong in a healthy diet.”
Author Nina Teicholz, a journalist who spent nine years reviewing 50 years of research and interviewing nutrition experts, told attendees at the North American Meat Association Outlook Conference in September that the switch away from a diet that includes saturated fats in meat, eggs and dairy has resulted in increased carbohydrate consumption, which has contributed to obesity and diabetes.
The Ohio State research was published in the Nov. 21 issue of the journal PLOS ONE.