Effect of butter and margarine intake on human milk CLA and fat concentrations in lactating women

Principal Investigators:

Mark McGuire, University of Idaho
Michelle McGuire, Washington State University
Kathy Beerman, Washington State University



Project Summary:

Lactating women were randomly assigned to a treatment sequence in a 3 x 3 Latin square design. Treatments consisted of muffins and cookies made with either 1) butter (containing CLA and no industrially-produced trans fatty acids), 2) regular margarine (containing no CLA and high amounts of industrially-produced trans fatty acids) and no trans margarine (containing either CLA nor industrially-produced trans fatty acids). Women consumed approximately 30 g of each lipid source daily for the 7-d periods. Milk samples were collected at the end of each period by complete breast expression. Milk composition was determined and fatty acid composition was analyzed using gas chromatography. Statistical analysis of the over-all Latin square design suggested that there was no effect of lipid source on milk fat or protein concentration. However, subsequent analyses showed a clear reduction in milk fat (40%) in lean subjects during the regular margarine period, as compared to the butter and no trans margarine periods. This is important as a relatively large literature suggests that milk fat percent is somehow influenced by body composition. It is possible that this may be mediated by dietary fatty acids. Further, we found a small but significant decrease in lactose concentration during the butter treatment. The fatty acid profile of milk was altered by dietary supplementation with the different lipid sources. Mean CLA concentration was highest during the butter period and lowest during the no trans margarine period; interestingly, consumption of regular margarine resulted in significantly higher milk CLA than consumption of no trans margarine. This suggests that women can produce CLA from fatty acids found in regular margarine. Further, butter consumption resulted in higher concentrations of palmitic acid in milk fat. Conversely, butter consumption decreased linoleic acid and linolenic acid concentrations compared to either margarine.


Masters, N., McGuire, M.A., Beerman, K., Dasgupta, N. and M.K. McGuire. 2001. Maternal supplementation with conjugated linoleic acid decreases milk fat in humans. Lipids, in press.

Precht, D., J. Molkentin, M.A. McGuire, M.K. McGuire, and R.G. Jensen. 2001. Overestimates of oleic and linoleic acid contents in materials containing trans fatty acids and analyzed with short packed gas-chromatographic columns. Lipids 36:213-216.

Jensen, R.G., M.A. McGuire, and M.K. McGuire. 2000. Trans fatty acids in human milk. Eur. J. Lipid Sci. Technol. 102:640-642.


None to date. However, these data will be the main focus of a master's thesis of Nicole Anderson. She will defend this thesis in Spring, 2002.

Published Abstract:

N Anderson, MK McGuire, MA McGuire, K Beerman, N Dasgupta, A Koepp, R Falen, JM Griinari and J Williams 2002 Consumption of "no trans" margarine decreases human milk and serum conjugated linoleic acid (CLA) concentrations. Submitted for presentation at the Experimental Biology meetings (April, 2002; New Orleans, LA).


Trans fatty acids: Is it the butterfat switch? and Feeding to manipulate CLAs in dairy products at the Pacific Northwest Animal Nutrition Conference, October 1999. Portland, OR.

"CLA; evidence that all fats aren't created equal" to the Idaho Dietetics Association, Lewiston, ID, April 26, 2001.

Documentation of CLA intake in humans: Potential health implications during the postpartum period for mothers and infants. Proc. 1st Inter. Conf. on Conjugated Linoleic Acid (CLA) in Alesund, Norway, June 2001.