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Newly published epidemiologic research goes a long way toward addressing two highly debated issues related to the health implications of dietary fat. More specifically, Chinese researchers provide evidence which supports a considerable amount of clinical data showing that the consumption of omega-6 polyunsaturated fat (PUFA) is not proinflammatory. In addition, U.S. researchers show that dairy fat can increase risk of cardiovascular disease but whether it does depends upon the macronutrient that replaces it in the diet.
The Chinese research consisted of a cross-sectional study involving 269 healthy participants (25-80 years old) from the Singapore Prospective Study Program who were selected by virtue of their falling into one of three predetermined dietary groups based on their fish and meat intake.1 Collectively, the results showed that high intake of red meat and high intake of fish increased plasma levels of arachidonic acid (AA). In contrast, neither the intake of omega-6 PUFA nor the intake of omega-6-PUFA-rich cooking oils (including soybean oil) was related to AA levels. However, such intakes were associated with higher levels of alpha-linolenic acid (ALA). Since fish and red meat are high in AA, these data show that preformed AA, but not its precursor linoleic acid ALA, is an important determinant of AA status. Consequently, these data refute concerns that omega-6 PUFA are proinflammatory. These concerns are based on the assumption that the intake of omega-6 PUFA increases endogenous levels of AA, which in turn will lead to the synthesis of proinflammatory eicosanoids.
The U.S. research consists of an analysis of data from three cohort studies: the Health Professionals Follow-Up Study (n=43,652 men), the Nurses' Health Study (n=87,907 women), and the Nurses' Health Study II (n=90,675 women).2 Dairy fat and other fat intakes were assessed every 4 years using validated food-frequency questionnaires. During 5,158,337 person-years of follow-up, there were 14,815 incident cardiovascular disease cases including 8974 coronary heart disease cases (nonfatal myocardial infarction or fatal coronary disease) and 5841 stroke cases.
Compared with an equivalent amount of energy from carbohydrates (excluding fruit and vegetables), dairy fat intake was not significantly related to risk of total CVD, coronary heart disease or stroke. However, replacement of 5% of energy intake from dairy fat with equivalent energy intake from PUFA was associated with a statistically significant 24% lower risk of CVD, whereas the 5% energy intake substitution of other animal fat with dairy fat was associated with a statistically significant 6% increased CVD risk. These data emphasize the important role that PUFA has in lowering risk of CVD.
Mark Messina, PhD, MS, is the co-owner of Nutrition Matters, Inc., a nutrition consulting company, and is an adjunct professor at Loma Linda University. His research focuses on the health effects of soyfoods and soybean components. He is chairman of The Soy Connection Editorial Board and executive director of the Soy Nutrition Institute.
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