Trans fats linked to infertility, reveals new study

Published this month in the American Journal of Clinical Nutrition​, the new study claims to be the first to examine the link between fat intake and infertility.

According to the scientists at Harvard School of Public Health in Boston, women ran a doubled risk of ovulatory infertility when they received two percent of their energy intake from trans fats rather than monounsaturated fats, which are contained in olive and canola oil.

Led by Dr Jorge Chavarro, the scientists examined the dietary intake of 18,555 women with no history of infertility who attempted a pregnancy between 1991 and 1999. During the examination period, participants were asked to complete two questionnaires listing almost 150 food items each. The women reported on how often during the previous year, on average, they had consumed each of the foods and beverages.

Nutrient intakes were estimated by summing the nutrient contribution of all food items in the questionnaire and taking into consideration the brand and type of margarine and the types of fat used in cooking and baking. The nutrient contents of each food and specified portion size were obtained from a nutrient database derived from the US Department of Agriculture (USDA), and additional information was obtained from food manufacturers.

During the eight-year follow-up, 3,430 women reported infertility, marked as an inability to conceive after one year.

According to the scientists' examinations, a two percent increase in energy intake from trans fatty acids was associated with a 94 percent greater risk of ovulatory infertility.

The association remained "significant"​ even after adjustment for other influencing factors, such as body mass index (BMI) and intake of alcohol and iron. Intake of saturated, monounsaturated and polyunsaturated fats had no association with infertility, said the scientists.

The findings will likely place even more focus on trans fats as the villain of food. The fats have already been repeatedly linked to raising LDL (bad) cholesterol levels, causing the arteries to become more rigid and clogged, and increasing the risk of heart disease.

This mounting scientific evidence and consequent media coverage has resulted in greater governmental and consumer awareness of the harmful effects of trans fats. Subsequent changes in labeling requirements to clearly reveal the trans fat content of foods has led to a sweeping reformulation effort in the US over the past few years, as food manufacturers attempt to slash the fats from their products.

The battle has also crept into the foodservice industry, with New York recently becoming the first city to ban the use of the fats in restaurants. Anti-trans campaigns are also well under way in other cities, which are expected to follow suit with similar moves in the near future.

Trans fatty acids - also known as trans fats - are formed when liquid vegetable oils are partially hydrogenated or 'hardened' for use as spreads such as margarine, cooking fats for deep-frying and shortening for baking.

The hunt for zero or low trans fat oils has led to an overall shift in demand in the vegetable oil market.

For example, there has been a recent increase in demand for traditional oilseeds that have been bred to have lower linoleic and linolenic acid levels to enhance oxidative stability (e.g. high oleic oil variants of soybean, canola and sunflower), as these are considered suitable alternatives to solid shortenings for frying and food processing. However there are still often issues of availability, as well as processing performance and product shelf life.

Tropical oils including palm oil, palm oil fractions, palm kernel oil, and coconut oil may also be used as alternatives to partially hydrogenated vegetable oil in some food processing applications because of their high melting points, but there can again be issues with flavor and functionality.