The effects of ruminant trans fatty acids and dairy food on cardiovascular disease and cardiometabolic risk.

Abstract

Background: Dairy food is the richest source of animal fats in the human diet and comprises saturated, unsaturated and trans fatty acids. There is lack of clear evidence on the effects of dairy fat, especially trans fatty acids, and food on cardiovascular health. This has led to incongruent advice on how much dairy fat and food is part of a healthy eating plan. Aim: To evaluate the effects of ruminant trans fatty acids and whole fat dairy food on cardiometabolic risk factors and cardiovascular disease. Methods: An observational study evaluated associations between plasma ruminant trans fatty acid levels and cardiovascular disease. A randomized study in 180 healthy adults assessed effects of changing dairy food intake on cardiometabolic risk factors and plasma levels of fatty acids. Fatty acid levels in whole milk and in plasma from vegans were evaluated. A meta-analysis evaluated the effects of dairy food on cardiometabolic risk. Results: The observational study suggests that two thirds of plasma trans fatty acids in New Zealanders with significant coronary artery disease are those thought to originate from ruminant sources. These trans fatty acids are associated with increased risk of recent myocardial infarction and polyvascular disease, but not increased mortality. However, in the randomized study, advice to change dairy food intake had little effect on fatty acids including saturated and trans fatty acids thought to be exclusively ruminant. Analyses of milk confirmed the presence of these trans fats, however; however, levels markedly varied between types of milk and between a year of normal rainfall and drought. Trans fatty acids, principally palmitelaidic acid were found in the plasma of vegans. The randomized study and a meta-analysis suggest that increasing whole and low fat dairy food increases weight but has no significant effects on other cardio-metabolic risk factors. Conclusion: The main source of trans fatty acids in the New Zealand diet is probably from dairy food. These fatty acids are associated with increased cardiovascular risk, suggesting that all trans fatty acids regardless of source may be harmful. However, modifying the intake of dairy food alone has no effect on plasma levels, and trans fatty acids were found in vegans implying that they are also from other sources. TFA levels in milk depend on feeding practices, suggesting that exposure to TFA in the diet could be reduced by changing farming practices. Increasing public awareness on all sources of TFA in the diet could be considered. Dietary advice to increase intake of low fat, and to a lesser extent whole fat dairy food, is associated with weight gain but has little effect on plasma fatty acids or cardio metabolic risk factors. Whilst small effects on cardiometabolic risks accumulating over a long period cannot be excluded, evidence suggests that dairy food is neither harmful nor beneficial for cardiovascular health. There is no evidence to support the traditional food pyramid approach to dietary advice where 3 or more servings of dairy food each day are recommended.