Fatty Acids in U.S. Milk

Milk can be a significant source of dietary fats. Many factors can influence its fatty-acid composition, especially the cows diet. The last survey of U.S. dairy milk fatty-acid composition was 25 years ago, in which timeframe there has been a substantial change in dairy feeds as well as analytical methods. A new study from Cornell University, Ithaca, NY, gives a picture of the current composition of retail milk in the United States.

Whole dairy milk contains 3.25% fat with more than 60% of that being saturated fats. The exact composition of milk has grown in interest as consumers are increasingly aware that food componentsincluding dietary fatty acidsmight influence human health maintenance and disease prevention.

The study, Survey of the fatty acid composition of retail milk in the United States including regional and seasonal variations, published in the January 2011 issue of the Journal of Dairy Science, looked at samples of fluid milk from 56 different U.S. milk processing plants every 3 months for a year to include any seasonal and geographical variations. The researchers selected plants that represented 50% or more of the fluid milk produced in that area.

Analysis of the milk showed that that saturated fatty acids comprised 63.7% of total milk fatty acids with palmitic and stearic acids representing the majority (44.1% and 18.3% of total saturated fatty acids, respectively). The milks unsaturated fatty acids comprised 33.2% of the total fatty acids, and consisted mainly of oleic acid (71.0% of total unsaturated fatty acids). These amounts were comparable to those of the 1984 milk survey. Trans fatty acids made up 3.2% of total fatty acids; the main trans isomer being vaccenic acid, which was 46.5% of total trans fatty acids. Cis-9, trans-11 18:2 conjugated linoleic acid represented 0.55% total milk fatty acids, and the major n-3 fatty acid (linolenic acid, 18:3) was 0.38%. There were some statistical differences for some fatty acids occurring due to seasonal and regional effects, but the scientists noted that they were minor from an overall human nutrition perspective because the fatty-acid profile for all samples were numerically similar.

The authors concluded that results demonstrate that U.S. milks fatty-acid profile is remarkably consistent across geographic regions and seasons from the perspective of human dietary intake of milkfat. This data adds to an earlier study (Survey of the fatty acid composition of retail milk differing in label claims based on production management practices, Journal of Dairy Science, Vol. 93, No. 5, May 2010, pp1918-1925) that found the fatty acid composition of conventional milk and milk labeled rbST-free or organic had no meaningful differences that would affect public health, and that all milks were similar in nutritional quality and wholesomeness.