Adam L. Lock, PhD, Fre´de´ric Destaillats, PhD, Jana Kraft, PhD, and J. Bruce German, PhD Department of Animal Science, University of Vermont, Burlington, Vermont (A.L.L., J.K.), Department of Food Science and Technology, University of California, Davis, California (J.B.G.), Nestle´ Research Center, Vers-chez-les-Blanc, Lausanne, SWITZERLAND (F.D.)
The symposium “Scientific Update on Dairy Fats and Cardiovascular Diseases” was held on 25 June 2008 in Reading (UK). The event was hosted by the University of Reading (UK) and organized and facilitated by the International Dairy Federation’s Standing Committee on Nutrition and Health. The objectives of this symposium were to provide a reappraisal of the impact of dairy foods and milk fat on cardiovascular diseases (CVD) and to place dairy fat into the context of overall human health.
An adequate supply of good quality food is essential for human health and well-being. It is unsurprising then that ruminant milk and dairy products have been recognised as important human food sources from as early as 4000B.C. as evidenced by the depiction of dairying in rock drawings from the Sahara and from cheese remains being found in Egyptian tombs dating back to 2300 B.C. . The dairy sector has made continuous advancement over the years and today there is a wide variety of milks and dairy products readily available to the consumer. In response to considerable scientific research on the nutritional value of milk, dietary guidelines around the world have recommended daily consumption of dairy products for the overall health of the population . The important contributions of these products in meeting human dietary requirements for energy, high quality protein and several key minerals and vitamins are well documented [3,4], although the nutritional importance of dairy fats is often less well understood. With the projected growth in world population and the increased demand for animal-derived food products as living standards improve, dairy products will undoubtedly continue to be an important dietary source of nutrients.
Food provides essential nutrients, but there is also growing
consumer recognition of the link between diet and health; this awareness impacts food choices. For over half a century, the concept of eating healthy has become synonymous with avoiding dietary fat and cholesterol, especially saturated fat, and on a population basis, a diet low in saturated fat remains at the heart of nutritional advice in many countries for lowering plasma cholesterol and reducing CVD risk. In the case of dairy products, there has been a general perception that a food containing saturated fat is unlikely to be beneficial to health. Yet, over the last decade, evidence has been accumulated that the composition and quantities of dietary fat is very important in determining the relative risk to diseases such as CVD and cancer, and that milk-derived fat may offer significant health benefits compared to some common sources of dietary fats [5–7].
On average bovine milk contains about 33 g total lipid (fat) per litre. Triacylglycerols, which account for about 97% of the lipid fraction, are composed of fatty acids of different carbon chain length (4 to 24 atoms), degree of saturation and positional specificity on the glycerol backbone. Other milk lipids are diacylglycerol (about 2% of the lipid fraction), cholesterol (less than 0.5%), phospholipids (about 1%) and free fatty acids (less than 0.5% of total milk lipids). Milk fat is present as complex globules with structural properties distinct from other biological sources of fats. It is one of the most complex naturally occurring fats with more then 400 different fatty acids reported, however, only about 20 of these make up approximately 95% of the total . It is important to recognize that a large diversity of dairy foods of widely differing composition is manufactured from this unique raw material.
Research continues to unravel the complexities associated with individual fatty acids and fats from different sources and it is becoming increasingly apparent that not all fatty acids, or saturated fatty acids, have the same biological effects. It is important to understand that the saturated fatty acids in milk vary in their structure and many have no effect on plasma cholesterol. This was highlighted by The Nutrition Committee of the American Heart Association whom emphasised the diversity in the biological effects of individual fatty acids and the need to evaluate specific fatty acids with respect to a range of variables related to the risk of coronary heart disease (CHD) . About 60% of the fatty acids in milk fat are saturated and of these there is consensus that 4:0, 6:0, 8:0, 10:0 and 18:0 have no effect on circulating cholesterol. Of the saturated fatty acids in milk fat, lauric (12:0), myristic (14:0) and palmitic (16:0) acid have been shown to increase plasma concentrations of total cholesterol and LDL-cholesterol when added as dietary supplements . The pattern of changes of circulating cholesterol in different lipoprotein fractions, however, is an important consideration since further advances in this area have established that lauric, myristic and palmitic acid may also result in increases in circulating HDL-cholesterol , a change that is associated with a reduced risk of CHD.
It is important to also recognize that individuals do not consume saturated fatty acids, or milk fat, as a dietary entity, but rather as fats in foods as part of an overall diet and investigations of the relationship of dairy product consumption and CVD also challenge the appropriateness of previous recommendations. As highlighted in this supplement, considering milk fat and dairy products within the context of overall health is a key consideration and in general, the available evidence does not provide support for the conclusion that consumption of dairy products adversely affects the risk of CVD. Clearly, the education of the public that fatty acids are not equal is required.
There is also increased recognition that foods contain ‘bioactive’ components that can affect health, and scientists are being asked to clarify the role of specific foods and food components in health maintenance and disease prevention . Consequently, the bioactive properties of a number of components in milk have been examined with regard to a range of health-related variables. Of special interest are the components associated with the prevention of chronic human diseases and results have demonstrated that milk contains specific proteins, peptides and fatty acids that are bioactive, while the production of fermented milk products also has been shown to have the potential to elicit beneficial effects on health-related variables. A partial list of the bioactive components in dairy products is highlighted in Table 1.
This supplement reflects the intellectual input from the invited speakers and their review of the scientific evidence related to the impact of dairy product consumption and milk fat in human diets on overall health and the risk of CVD. Additional information can be found in German et al. , which presents an overview of this symposium, general consensus of the invited speakers, thoughtful discussions of the conference participants, and future suggestions for milk fat-human health research. The symposium was convened with over 50 internationally recognized experts in dietary fats and human health and addressed topics and issues related to:
• The collective body of scientific evidence on the effects of dairy food consumption from cohort studies on CVD, diabetes and cancer
• The effects of dairy fats within different foods on plasma lipoproteins
• The effects of dairy products on non lipid risk factors for CVD
• The role of dairy products as essential contributors of micronutrients in reference food patterns and what effects recommending further reductions in dairy food consumption, to attain saturated fatty acid intake targets, would have on nutrient status at a population level
• The importance of recognising that saturated fatty acids in the diet come in a package along with other nutrients and are not consumed as a single dietary entity and the difficulty and inappropriateness of divorcing any discussion of dairy fat from dairy foods
• Identify areas of scientific agreement regarding the health effects of saturated fatty acids in milk and milk consumption per se on human health, as well as areas for further research
• Consider whether the current body of science for milk fat and CVD is consistent with current dietary recommendations which propose reducing dairy fat consumption as a means of reducing intake of saturated fatty acids.
In summary, this symposium provided a unique opportunity for researchers and experts from around the world with expertise in the area of milk, fats and human health to come together and review the available scientific evidence relating dairy products and milk fat to CVD risk. The information presented at this symposium and reviewed in this supplement highlight that despite the contribution of dairy products to the saturated fatty acid composition of the diet there is no clear evidence that dairy food consumption is consistently associated with a higher risk of CVD. Given the diversity of available dairy foods of widely differing composition and their contribution to nutrient intake within the population, recommendations to reduce dairy food consumption irrespective of the nature of the dairy product should be made with caution.
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4. National Research Council: “Designing Foods: Animal Product Options in the Marketplace.” Washington DC: National Academy Press, 1988.
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13. German JB, Gibson RA, Krauss RM, Nestel P, Lamarche B, van Staveren WA, Steijns JM, de Groot LCPGM, Lock AL, Destaillats F: A reappraisal of the impact of dairy foods and milk fat on cardiovascular disease risk. Eur J Nutr, in press, 2008.