As I am still waiting for my little one to make her grand entrance, I thought I would look into detail at a nutrient found in breast milk that seems to be getting a lot of media attention at the moment – the essential fatty acids DHA and AA.
Breast milk contains essential fatty acids – these are components of fats that must be provided by the diet. The most well known essential fatty acids in breastfeeding are arachidonic acid (AA) and docosahexaenoic acid (DHA). AA makes up part of cell membranes and are used to make signalling molecules in the body. DHA is also part of cell membranes, particularly in the retina and brain.
Normal breast milk contains both these essential fatty acids, and their precursors. The concentration of AA is fairly constant at 0.35 – 0.7 % by weight of the fatty acids in breast milk, whereas there is a lot more variation in DHA concentrations from 0.17 – 1.0 % by weight. To put that in perspective, the total lipid content of breast milk is around 4 g per 100 ml.
The concentration of AA in breast milk probably does not change too much because it is synthesised from linoleic acid (LA), which is a significant component of the most widely-used oils in the world (e.g. sunflower oil, corn oil, peanut oil, soy bean oil). The DHA content of breast milk varies more widely – the conversion of DHA from the more widely consumed alpha-linolenic acid (ALA) is poorer and ALA is found in lower amounts in oils used in normal diets. Just to illustrate this point, the commonly used oils corn, cottonseed, sunflower and soybean oil all contain over 50% LA, according to the wikipedia links. The only oil that is likely to be easy to find in the average supermarket with more than 50% ALA is linseed oil, and the more common canola and soybean oil contain only around 10% ALA. DHA is also naturally found in only fatty fish and very few other sources. A company that makes DHA from algae has provided a DHA calculator that illustrates the most common food sources of DHA. So this is probably why there is so much more variation in DHA concentrations in breast milk.
Recently, there have been moves to make recommendations to pregnant and lactating women about how much DHA they should be consuming. Once the concentration of DHA in breast milk exceeds 0.8 % of the fatty acids, there is no further increase in red blood cell DHA and this is considered to be the plateau (Gibson, 1997). Another study found a plateau of 0.5 %, acheived with 200 mg DHA from 21 weeks of pregnancy (Bergmann, 2008). Current recommendations are around 200 mg DHA per day, or two servings of fatty fish per week.
I borrowed heavily from the information in this review and consensus statement:
Koletzko B, et al. (2008) Recommendations and guidelines for perinatal practice: The roles of long-chain polyunsaturated fatty acids in pregnancy, lactation and infancy: review of current knowledge and consensus recommendations J. Perinat. Med. 36 (2008) 5–14 DOI 10.1515/JPM.2008.001 http://www.ncbi.nlm.nih.gov/pubmed/18184094
My other references were:
Bergmann, BL et al. Supplementation with 200 mg/Day Docosahexaenoic Acid from Mid-Pregnancy through Lactation Improves the Docosahexaenoic Acid Status of Mothers with a Habitually Low Fish Intake and of Their Infants. Annals of Nutrition and Metabolism. Vol. 52, No. 2, 2008. http://www.ncbi.nlm.nih.gov/sites/ppmc/articles/PMC2790529/
Fidler N, Sauerwald T, Pohl A, Demmelmair H, Koletzko B. (2000) Docosahexaenoic acid transfer into human milk after dietary supplementation: a randomized clinical trial. J Lipid Res. Sep;41(9):1376-83. http://www.ncbi.nlm.nih.gov/pubmed/10974044
Gibson RA, Neumann MA, Makrides M. (1997) Effect of increasing breast milk docosahexaenoic acid on plasma and erythrocyte phospholipid fatty acids and neural indices of exclusively breast fed infants. Eur J Clin Nutr. 51: S78–84. http://www.ncbi.nlm.nih.gov/pubmed/9306083
The DHA calculator is provided by Life’sDHA, and is based on a typical American diet – fried catfish with cornbread and steamed broccoli, anyone? The fish products are the only sources of DHA as far as I can see. http://www.lifesdha.com/dha-calculator.aspx