If milk does the heart good, it might do even more if it comes from dairy cows grazed on grass instead of on feedlots, according to a US study.
Earlier studies have shown that cows on a diet of fresh grass produce milk with five times as much of an unsaturated fat called conjugated linoleic acid (CLA) than cows fed processed grains.
Studies in animals have suggested that CLAs can protect the heart, and help in weight loss.
Hannia Campos of the Harvard School of Public Health in Boston and her colleagues found in a study of 4000 people that those with the highest concentrations of CLAs - the top fifth among all participants - had a 36% lower risk of heart attack compared to those with the lowest concentrations.
Those findings held true even once the researchers took into account heart disease risk factors such as high blood pressure and smoking.
Campos says these new findings, published in the American Journal of Clinical Nutrition, suggest that CLA offers heart-healthy benefits that could more than offset the harms of saturated fat in milk.
"Because pasture grazing leads to higher CLA in milk, and it is the natural feed for cattle, it seems like more emphasis should be given to this type of feeding," says Campos.
Dairy products in the United States come almost exclusively from feedlots, she says, and cow's milk is the primary source of CLA. Beef contains a small amount.
'Not the villain'
For their study, Campos and her colleagues looked to Costa Rica where pasture grazing of dairy cows is still the norm.
They identified nearly 2000 Costa Ricans who had suffered a non-fatal heart attack, and another 2000 who had not. They then measured the amount of CLA in fat tissues to estimate each person's intake.
Since CLA typically travels with a host of other fats, the researchers went a step further to tease apart its effects from those of its predominantly unhealthy companions.
The difference in risk attributed to CLA subsequently rose to 49%.
"Whole-fat milk and dairy products have gotten such a bad reputation in recent years due to their saturated fat and cholesterol contents, and now we find that CLA may be incredibly health-promoting," says Michelle McGuire, spokesperson for the journal's publisher, the American Society for Nutrition. "Whole milk is not the villain."