AJCN.org – Dietary recommendations related to maintaining a healthy heart routinely suggest substituting low-fat or nonfat dairy products for their full-fat counterparts. However, a growing literature is beginning to question this long-held and dogmatic belief, with several studies actually documenting inverse relations between dairy products and cardiovascular risk. Furthermore, researchers have identified compounds relatively unique to milk fat (e.g. conjugated linoleic acid, or CLA) with potentially heart-healthy properties. The July 2010 issue of The American Journal of Clinical Nutrition presents results from 2 independent studies that carefully examined whether dairy fat consumption is related positively or inversely to risk of myocardial infarction (heart attack).

Both studies employed “case-control” designs in which a group of individuals (cases) who had experienced a heart attack were compared with another group (controls) who had not. The first study, conducted in Sweden, included 444 cases and 556 controls. Participants provided information on cardiovascular risk factors (e.g. smoking) and diet; blood samples were collected and analyzed for 2 fatty acids somewhat unique to dairy fat (15:0 and 17:0). The second study took place in Costa Rica and compared 1,813 cases with 1,813 controls. In addition to assessing basic information concerning cardiovascular disease risk factors and diet, the researchers also obtained a subcutaneous adipose tissue sample taken from the upper buttock region. These samples were analyzed for their content of CLA (9c,11t-18:2), a naturally-occurring fatty acid found almost exclusively in whole milk and beef products.

The Swedish researchers found that, in women, proportions of 15:0 and 17:0 in plasma were higher (P < 0.05) in controls than in cases; in fact, having the greatest amount of these fatty acids was associated with a 26 percent lower risk of heart attacks in women. A similar trend was found for men, but it was not statistically significant. Even stronger relations between dairy fat intake and heart attack risk were reported from the Costa Rican study. After control for a variety of factors such as saturated and trans fat intake, study participants with the lowest concentrations of adipose tissue CLA were 49 percent more likely to be cases than controls. As would be expected, subjects with the highest adipose tissue CLA also had the highest intakes of dairy products.

Although these results might seem counterintuitive because dairy fat also contains high proportions of saturated fat and cholesterol, they fit with a growing literature suggesting that dairy foods, per se, may be associated with a lower risk of heart disease.

References: Smit LA, Baylin A, Campos H. Conjugated linoleic acid in adipose tissue and risk of myocardial infarction. American Journal of Clinical Nutrition. July 2010;92:34–40.

Warensjö E, et al. Biomarkers of milk fat and the risk of myocardial infarction in men and women: a prospective, matched case-control study. American Journal of Clinical Nutrition. July 2010;92:194–202.