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Trans fats, pregnancy, breast feeding and babies

Dietary trans fats from hydrogenated vegetable oil find their way, unaltered, across the placenta of pregnant women and into the growing foetus. They contribute to low birth weight and mothers who consume trans fats are more likley to suffer pre-eclampsia.

The damage continues after birth, as trans fats in the mother's diet also contaminate their milk. These trans fats in human milk displace 'essential fatty acids' (such as omega-3 fatty acids) that help the baby, and specifically the baby's brain and nervous system, to grow and develop. In addition, dietary trans fats reduce overall fat levels in milk. It is also known that dietary trans fats inhibit assimilation of essential fatty acids, so the children of mothers who eat a trans fat-loaded diet suffer a nutritional "double double whammy".

Our advice is that if you are intending to become pregnant, if you are pregnant, or if you are a breast-feeding mother, do everything you can to avoid eating trans fats for the sake of your baby's health.

It has been estimated that, if a person stops eating trans fats altogether on a given date, it will take approximately two years for the residual trans fat in their bodies to be cleared through by the natural turnover of fat in body tissue. We would therefore advise women to try and avoid dietary trans fat for two years before becoming pregnant, not only to avoid passing trans fat to the baby in milk, but also to prevent trans fat being incorporated directly into the foetus.

In this regard, a German study found a correlation between the consumption of trans-fatty acids by mothers and low birth weight in infants ["Trans fatty acids may impair biosynthesis of long-chain polyunsaturates and growth in man", by B. Koletzko, Acta Paediatr., 1992, April 81(4): 302-6]. According to Dr. Sheila Innes of the University of British Columbia, babies born with higher levels of trans fat have lower levels of essential omega 3 fatty acids: "With trans fatty acids, if they are high in the diet, the essentially fatty acids are low".

For information on pre-eclampsia see "Risk of Preeclampsia in Relation to Elaidic Acid (Trans Fatty Acid) in Maternal Erythrocytes" by Williams M. A. et al, (Gynecol Obstet Invest 1998; 46: 84-7).

How much trans fat is there in mothers' milk?

A 1992 study of 198 Canadian mothers by the Nutrition Research Division of Health Canada found that the fat in human milk contained an average of 7.2 percent trans fat, ranging across the sample from 0.1 to 17.2 percent. Analysis of the trans fats showed that they came from hydrogenated vegetable oils. The work was led by Professor Chen Zhen Yu of the Department of Biochemistry of The Chinese University of Hong Kong.

In a simultaneous sample of 51 Hong Kong Chinese women, he found an average of just 0.88 percent trans fat in their milk, reflecting their lower dietary intake of hydrogenated oil. A sample of 33 mainland Chinese women found just 0.22 percent of trans fat in their milk.

The study also examined the effect of feeding trans fats to lactating rats. A positive correlation was found: rats on a 10 percent trans fat diet produced milk with six percent of trans fat, while rats on a 25 percent trans fat diet produced milk with 16 percent trans fat (as percent of fat content).

In another aspect of the study, newborn and maternal rats were fed with large doses of trans fat. It was observed that the trans fat accumulated in the heart, kidney, and liver, in the place of natural cis-fatty acids. Over consumption of trans fat also interfered with the metabolism of essential fatty acids in newborn rats.

In the light of his findings, Professor Chen advises lactating mothers to reduce their intake of hydrogenated fats.

See an abstract of the paper here. ["Trans fatty acid isomers in Canadian human milk", Lipids 1995 Jan; 30(1):15-21, by Chen Z. Y., Pelletier G., Hollywood R, Ratnayake W. M., of the Nutrition Research Division, Health Protection Branch, Health Canada, Ottawa, Ontario.] See also a summary of Professor Chen's work here.

Reductions in essential fatty acids in human milk

Research by Sheila M. Innis and D. Janette King in 1999 based on a sample of 103 Canadian mothers found that "trans Fatty acids in human milk are inversely associated with concentrations of essential all-cis n-6 and n-3 fatty acids and determine trans, but not n-6 and n-3, fatty acids in plasma lipids of breast-fed infants".

See their paper here. [American Journal of Clinical Nutrition, Vol. 70, No. 3, 383-390, September 1999].

Research also indicates that trans fats in the diet of lactating mothers reduces the overall fat content of milk. See here ["Milk fat depression in C57Bl/6J mice consuming partially hydrogenated fat", Journal of Nutrition 1990 August;120(8):818-24, by Teter B. B., Sampugna J., Keeney M., Department of Chemistry and Biochemistry, University of Maryland, College Park 20742].

Both Omega-3 and Omega-6 essential fatty acids are necessary for the proper development of foetal and infant tissues, especially the brain and nervous system. Omega-3s affect parts of the brain relating to learning ability, mood, and perception, specifically the development of the eye and visual system.

According to Dr Donald Rudin, writing in The Omega-3 Phenomenon,

"American mothers produce milk that often has only one-fifth to one-tenth of the omega-3 content of the milk that well-nourished, nut-eating Nigerian mothers provide their infants."
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