Research Sheds Light on Fat and Inflammation
By Mark Messina, PhD, Executive Director, Soy Nutrition Institute
Fat is back. Not that it ever really went away. Even when very low-fat diets were all the rage, experts recognized that certain fats were more harmful than others and some were even beneficial.
A common misperception is that omega-6 polyunsaturated fats, which are found in abundant amounts in most oils, including soybean oil, are pro-inflammatory. Meanwhile, it is thought that omega-3 polyunsaturated fats protect against inflammation. Chronic inflammation is believed to be a key process underlying many chronic diseases.
Back in the late 1970s, researchers suggested that the low incidence of heart disease among the Inuit of Canada and Alaska was related to their fat intake.1 Specifically, this population eats a diet high in the omega-3 fatty acid eicosanoic acid from fish and low in the omega-6 fatty acid arachidonic acid which is found in other types of meat.
The findings put omega-3 fats in the spotlight, giving rise to the popularity of fish oil supplements. But evidence in support of the health benefits of omega-3 fat has never been as consistent as anticipated. In fact, recent commentaries published in two distinguished medical journals reached completely opposite conclusions about the benefits of omega-3 fat supplementation.2,3
Likewise, the harmful effects of saturated fat have been brought into question recently. It is now recognized that while saturated fat raises LDL-cholesterol, it also increases LDL particle size; large LDLs are less atherogenic than small LDLs.4 Nevertheless, prospective epidemiologic studies clearly show that replacing saturated fat with omega-6 polyunsaturated fat reduces CHD risk and mortality.5,6 And in the end, it’s this relevant endpoint—heart disease—that matters.
While replacing saturated fat with complex carbohydrates also reduces risk, the beneficial effects are smaller compared to omega-6 fats. Which raises this question: If omega-6 fats increase inflammation why would replacing saturated fat with omega-6 fat reduce CHD risk?
Part of the explanation is that omega-6 fats reduce serum LDL-cholesterol. More importantly, despite the common perception, the proinflammatory effects of omega-6 fat aren’t very well established. In fact, a systematic review of clinical trials published in 2012 concluded that there is “virtually no evidence” from clinical trials that linoleic acid, the main dietary omega-6 fat, increases concentrations of inflammatory markers in healthy people.7
This finding may seem surprising since it is thought that in vivo, linoleic acid is converted into arachidonic acid, the omega-6 fat from which the alleged proinflammatory hormones (eicosanoids) are produced. However, extensive clinical research shows that increasing linoleic acid intake has little effect on endogenous levels of arachidonic acid.8 Furthermore, not all of the eicosanoids produced from arachidonic acid are pro-inflammatory.9
These findings will hopefully change the way that different fats and oils are viewed in healthy diets. Until the dust settles, it’s clear that soybean oil is a choice that provides the best of all worlds, since it is rich in both omega-6 and omega-3 fats. While ideally most dietary fat should come from whole foods, added fats and oils can play important culinary roles.