Replacing Saturated Fat With Polyunsaturated Fats--Not Carbs--Reduces CHD Risk

March 23, 2010

March 23, 2010 (Boston, Massachusetts) — Replacing dietary saturated fats with polyunsaturated fats significantly reduces the risk of coronary heart disease events, a new study has shown [1]. The findings, say investigators, highlight the importance of replacing saturated fat with healthy food choices, such as fish and vegetable oils, in order to get the heart-protective benefits of a low–saturated-fat diet.

"For 60 years we've been recommending reduced saturated-fat consumption without a focus on what should replace it in the diet," lead investigator Dr Dariush Mozaffarian (Harvard University, Boston, MA) told heartwire . "In practice, what's happened, if you look at trends over the past decade, saturated fat has been replaced by carbohydrates, largely refined carbohydrates. There have been several recent meta-analyses of observational studies showing that if you reduce saturated fat and don't pay attention to the replacement, there is no association with lower heart-disease events."

Mozaffarian pointed to a recent meta-analysis of prospective epidemiologic studies showing that there was no significant evidence that dietary saturated fat is associated with an increased risk of coronary heart disease or cardiovascular disease [2].

"This is pretty important on a policy level," said Mozaffarian. "It's naturally assumed that lowering saturated fat is good for the heart, but that's not what the evidence shows." Simply reducing saturated fat without regard to what is substituted for it might not derive any benefit, he said.

The results of the study are published online March 23, 2010 in PLoS Medicine.

Meta-Analysis of Eight Trials

In this newest meta-analysis, the researchers hypothesized that polyunsaturated fats might be the ideal replacement nutrient for saturated fats. They performed a systematic review of studies that randomized patients to polyunsaturated fats for at least one year without any additional medications, had an appropriate control group, and reported the incidence of coronary heart disease, defined as MI and/or cardiac death. In total, eight trials were included, with 13 614 participants and 1042 coronary heart disease events.

The average weighted consumption of polyunsaturated fats was 14.9% of energy consumption in the intervention groups compared with 5.0% of energy from the controls. The risk of MI and/or cardiac death was reduced a significant 19% for those who consumed more polyunsaturated fats. With each 5% increase in the percentage of energy from polyunsaturated fats, there was a 10% reduction in the risk of coronary heart disease.

"We found that there was a significant overall benefit in using polyunsaturated fat as a replacement for saturated fat, and this benefit was about a 20% reduction in heart disease for the exchange the individuals made," said Mozaffarian. "Most of the trials used soybean oil or other vegetable oils that have a little bit of omega-3 fatty acids, but the great majority of polyunsaturated fats in the diet, 90% to 95%, were omega-6 fatty acids."

To put the results in context, the researchers pulled evidence from other studies looking at replacing saturated fats with carbohydrates and report that there is no benefit to individuals, "which is striking because this is what we've been doing for the past 50 or 60 years," said Mozaffarian. There are few studies examining replacing saturated fats with monounsaturated fats, he added, so no conclusions can be made about this source of energy.

"These findings are relevant for industry and consumers because industry is trying to reduce trans fat and replace saturated fat in food, and polyunsaturated fat should be the preferred replacement, if at all possible," continued Mozaffarian. "Consumers don't think one-to-one about replacing foods, but if you're trying to reduce saturated fats and just eating a lot of low-fat, high-carbohydrate foods instead, rather than a healthy overall diet, you're probably not going to get the benefit of these low–saturated-fat diets."

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