Replacing milk saturated fatty acids for improved cardiovascular health: how strong is the evidence?
The November Nutrition Society Paper of the Month is ‘The impact of substituting SFA in dairy products with MUFA or PUFA on CVD risk: evidence from human intervention studies’. With the substantial economic and social burden of CVD, the need to modify diet and lifestyle factors to reduce risk has become increasingly important. Milk and dairy products, being one of the main contributors to SFA intake in the UK, are a potential target for dietary SFA reduction. Review author Katherine Livingstone discusses this below.
The present review summarises findings from nine chronic human intervention studies, where consumption of a control milk or dairy product and one that had been modified through bovine diet to have lower saturated fatty acid (SFA) content were compared to evaluate their effect on markers of cardiovascular disease (CVD) risk.
Studies by Tholstrup et al. (1998), Noakes et al. (1996) and Seidel et al. (2005) fed cows a rapeseed-based diet (a source of MUFA) and achieved reductions in milk SFA of 10, 17 and 19 % respectively. Studies that fed a source of n-6 PUFA, Tholstrup et al. (2006) and Lacroix et al. (2012), achieved reductions of 13.8 and 14.2 % respectively. In the studies that fed cows n-3 PUFA, Malpuech-Brugere et al. (2010), Legrand et al. (2010) and Weill et al. (2002), reductions in the proportions of SFA were 15.4, 6.2 and 6 %. In contrast to all the other studies, these studies adopted ‘livestock’ approaches, thereby altering the FA concentration of not only dairy products but also other animal products such as eggs and pork.
All studies based estimates of CVD risk on changes in total cholesterol and low- and high-density lipoprotein (LDL/HDL) cholesterol concentrations. Poppitt et al. (2002), Tholstrup et al. (2006) and Lacroix et al. (2012) also included inflammatory markers, yet saw no significant changes in these markers between dairy products.
Large variations in study designs, including the choice of fat supplement, choice of milk or dairy product tested (where butter was the main product of choice), number of subjects, meant that direct comparison between studies was limited. Furthermore, upon closer inspection of the fatty acid composition of the test products and the diets, it became apparent that other sources of dietary fat were introduced into three of the study diets, which meant changes in cholesterol concentrations may not have been solely driven by the test products. Three other studies also provided incomplete fatty acid information.
Nonetheless, of the eight studies that measured blood cholesterol, four reported a significant reduction in total and LDL-cholesterol following chronic consumption of modified milk and dairy products. Seidel et al. (2005) was the only study to show an increase in HDL-cholesterol, and was also the only study to compare responses in normo- and hyper-cholesterolaemic subjects. Seidel et al. (2005) suggested that a significant reduction in LDL-cholesterol could be achieved in both the normo- and hyper-cholesterolaemic population.
Thus, evidence from these studies suggests that consumption of milk and dairy products with modified fatty acid composition, compared with milk and dairy products of typical milk fat composition, may be beneficial to CVD risk in healthy and hyper-cholesterolaemic individuals.
However, current evidence is limited by small sample sizes, lack of evidence for individual milk and dairy products, use of transitory markers to estimate CVD risk and incomplete fatty acid information. Further randomised controlled trails are needed to investigate the complex role of milk and cheese in CVD risk and explore the use of novel and more holistic markers of CVD risk.
Nutrition Society Paper of the Month
Each month a paper is selected by one of the Editors of the five Nutrition Society Publications (British Journal of Nutrition, Public Health Nutrition, Nutrition Research Reviews, Proceedings of the Nutrition Society and Journal of Nutritional Science). This paper is freely available for one month.