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Diet Guidelines Favoring Vegetable Fats Refuted

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In turn, Ramsden's investigators included their Sydney conclusions in a new review of all studies to date exploring the impact of omega-6 consumption.

Despite the fact the American Heart Association (AHA) currently recommends that 5 percent to 10 percent of all calories come from polyunsaturated fat (principally from omega-6), the NIH team found no evidence to support the notion that linoleic acid confers health benefits. The review highlighted the possibility that boosting omega-6 consumption may actually increase the risk for developing heart disease.

Ramsden acknowledged that the Sydney study had been narrowly focused on a specific group of people: middle-aged men with a history of heart disease, who were asked to consume linoleic acid in quantities far exceeding both AHA guidelines and the dietary habits of most Americans.

"So, yes, one of the limitations of this kind of study is always the question of its generalizability to other populations," he cautioned.

But he also suggested that his team's rigorous look back offered valuable insights into how nutritional science has evolved.

"What to many people had at one time seemed pretty straightforward in the 1960s has turned out to form a much less black-and-white picture," he said. "Polyunsaturates are not just involved in cholesterol-lowering. They may also be involved in inflammation, oxidation or clotting. So, it's a very complex picture. And though our goal is not to come up with diet advice, it may be that our conclusions will have important implications for nutritional guidelines."

On that score, American Heart Association spokesperson Penny Kris-Etherton, a registered dietician and professor of nutrition at Pennsylvania State University, suggested that the controversy concerning linoleic acid is not new and will continue.

"But I don't think this is going to change AHA recommendations," she said. "Because there's very robust evidence showing the cardiovascular benefit of linoleic acid. The AHA science advisory board did not just look at one study or a couple of studies. There are lots of studies that form the basis for their guidelines."

"So, I don't think anybody should get alarmed and change their diet," Kris-Etherton said. "Those who are concerned should wait for more research to come out on this topic before taking any drastic measures to change their eating habits in a way that could be harmful."

More information

For more on AHA guidelines regarding linoleic acid, visit the American Heart Association.

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