Full-fat dairy reduces cardiovascular disease?

Studies examining the epidemiological effect of a food rarely disclose its quality and source. Do you ever wonder if a study on meat, for example, might give different results if the subjects consumed only organic grass-fed meat rather than meat from hormone and antibiotic-laced feedlot animals fed on grain silage and offal? A study recently published in the European Journal of Clinical Nutrition came up with a surprise when it investigated the effect of full-fat dairy on cardiovascular disease in Australian adults.

"Dairy foods contain various nutrients that may affect health. We investigated whether intake of dairy products or related nutrients is associated with mortality due to cardiovascular disease (CVD), cancer and all causes."

The authors studied 1529 adult Australians over 16 years, correlating habitual intakes of dairy products with mortality and cause of death. When the numbers were analyzed an unexpected finding emerged:

"...compared with those with the lowest intake of full-fat dairy, participants with the highest intake had reduced death due to CVD after adjustment for calcium intake and other confounders."

The data compelled them to record conclusions contrary to popular dogma:

"Overall intake of dairy products was not associated with mortality. A possible beneficial association between intake of full-fat dairy and cardiovascular mortality needs further assessment and confirmation."

Perhaps it has something to with what the cows were eating. A study published just last month in the journal Veterinary Research Communications compared the effect of grass hay versus grain (maize = corn) on the properties of the milk to promote cardiovascular disease.

"14 Holstein dairy cows were fed...either grass hay (GH) or maize silage (MS). Milk samples were collected...and fatty acid (FA) profiles were analyzed...Milk from animals fed the GH-diet contained lower concentrations of saturated FAs and higher levels of polyunsaturated FAs (PUFAs). Feeding additional hay also increased conjugated linoleic acid and n-3 FA levels and decreased C16:0 levels."

What do these differences in fatty acids mean for cardiovascular disease risk?

"Increases in both PUFAs and n-3 FAs resulted in lower atherogenic and thrombogenic indices in milk from animals fed the GH diet compared with those fed the MS diet. A complete substitution of GH for MS appeared to improve milk FA profiles...."

Too bad the authors of the Australian study weren't able to specify what those Australian cows ate. But another fascinating study just published in the American Journal of Clinical Nutrition sheds more light on the matter. The authors begin by observing:

"Despite the high saturated fat content of dairy products, no clear association between dairy product intake and risk of myocardial infarction (MI) has been observed. Dairy products are the main source of conjugated linoleic acid (CLA; 18:2n–7t), which is produced by the ruminal biohydrogenation of grasses eaten by cows. Pasture-grazing dairy cows have more CLA in their milk than do grain-fed cows. Some animal models have reported beneficial effects of CLA on atherosclerosis."

The authors wanted to determine the association between CLA in adipose tissue and risk of MI [myocardial infarction]. They used 1813 individuals with non-fatal heart attacks compared to matched controls, in Costa Rica where people use traditional pasture-grazing for dairy cows. What did their data show?

"Adipose tissue CLA was associated with a lower risk of MI...Dairy intake was not associated with risk of MI, despite a strong risk associated with saturated fat intake."