The comparison between
cis -fatty acid and trans -fatty acid
Before You Swap Butter for Margarine
Adverse Health Effects of Hydrogenated Vegetable Oils
It is well known that too much animal fat in the diet can increase the risk of cardiovascular disease, cancer, diabetes, obesity, and other chronic diseases. Animal fats such as beef tallow and lard contain cholesterol and a higher level of saturated fatty acids than vegetable oils such as corn, soybean, rapeseed, and sunflower oil. The latter are believed to have fewer adverse effects on health due to the absence of cholesterol and their higher unsaturated fat content.
Yet vegetable oils remain in liquid form because of their lower melting point, and hence do not offer the convenience of, say, being spreadable like butter. Besides they go bad easily: food that has been cooked with vegetable oils do not keep. Food manufacturers at the turn of the century invented a process called 'hydrogenation' which converts vegetable oils into 'vegetable shortening' by catalyzing them with hydrogen and certain metals in the presence of heat. In the last decade food manufacturers and fast food restaurants have switched to using hydrogenated vegetable oils because they are less expensive and because food cooked with them has a longer shelf life. It was also found that when partially hydrogenated, vegetable oils become margarine, which quickly replaced butter in the market due to its lower cost and 'healthier' image.
Hydrogenated Vegetable Oil is Unhealthy
But while the world was believing that vegetable oils were a healthier alternative to animal fats, studies showed hydrogenated vegetable oil could be a health hazard.
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The comparison between
cis -fatty acid and trans -fatty acid
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A research conducted by Harvard University found that people consuming more trans-fatty acids have a higher risk of cardiovascular disease. Another study published in Lancet showed that the consumption of hydrogenated vegetable oils by 85,095 nurses over an eight-year period had increased the occurrence of coronary heart diseases among them. And Dutch researchers found that volunteers on a trans-fatty acid diet have 20-30 mg more serum cholesterol than those on a cis-fatty acid diet. These findings cast doubts on the widespread use of hydrogenated vegetable oils in Western fast food restaurants. The effects of trans-fatty acids on health becomes a controversial issue.
Mother-Infant Transfer of Trans-Fatty Acids
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Prof. Chen Zhen Yu of the Department of Biochemistry of The Chinese University found a positive correlation between the level of consumption of trans-fatty acids by lactating Canadian women and the trans-fatty acid content in their breast milk, in a study he conducted in 1992 as a research fellow at the Nutrition Research Division of the Department of Health in Canada. This means that trans-fatty acids present in partially hydrogenated vegetable oils are transferred to human milk through maternal diets. Another study conducted by German researchers found a correlation between the consumption of trans-fatty acids by mothers and low birth weight in infants.
It is estimated that North Americans consume approximately 10g of trans-fatty acid per day. As the diet of Hong Kong's population becomes more westernized, does it also mean that Hong Kong women are consuming more trans-fatty acids.' In 1995 Prof. Chen began the project 'Metabolic Rate of Trans-/Cis-Fatty Acids Present in High-Trans Milk and Their Effect on metabolism of Essential Fatty Acids' The project was supported by a HK$1,180,000 grant from the Research Grants Council.
Trans-Fatty Acid Content of Hong Kong Maternal Milk
The study was divided into two parts. One part investigated the fatty acid composition of the breast milk of 51 Hong Kong Chinese women and compared it with that of 33 mainland Chinese and 198 Canadian women. It was found that Hong Kong Chinese breast milk contained 0.88 per cent of trans-fatty acid, while mainland Chinese breast milk contained 0.22 per cent, and Canadian breast milk, 7.19 per cent.
Adverse Effects of Trans-Fatty Acids
The study's other part investigated the relation between the amount of trans-fatty acids in maternal diet and that in maternal milk by putting lactating rats on diets with varying levels of the acids in question and analyzing their milk. A positive correlation was found: rats on a 10 per cent trans-fatty acid diet produced milk with six per cent of the acid while rats on a 25 per cent diet produced milk with 16 per cent.
Prof. Chen and his colleagues also found adverse effects associated with feeding newborn and maternal rats with large doses of trans-fatty acids. They could accumulate in the heart, kidney, and liver, in the place of natural cis-fatty acids. Over consumption of trans-fatty acids also interferes with the metabolism of essential fatty acids in newborn rats. Although the adverse effects of trans-fatty acids in maternal milk have not been confirmed, Prof. Chen advises lactating mothers to reduce their intake of both saturated and hydrogenated fats.
Prof. Chen Zhen Yu graduated
with a BSc in chemistry from Henan Normal University in 1982. He then
went abroad to the US where he obtained his PhD in food and nutritional
science from the University of Massachusetts (Amherst) in 1989. For
the next five years, he was first postdoctoral fellow in the Department
of Nutritional Science at the University of Toronto, then research fellow
at the Nutrition Research Division of the Department of Health, Canada.
He joined The Chinese University in 1994.