Trans Fatty Acids and Soybean Oil Backgrounder

During the 1960s and 1970s, consumers demanded that food companies eliminate fats such as lard, beef tallow and tropical oils (i.e., palm, palm kernel and coconut oils) from their products in order to reduce saturated-fat content. In many applications, the higher-saturate oils were replaced with partially hydrogenated vegetable oils (fully hydrogenated oils are very seldom used). Hydrogenated oils have hydrogen atoms added to make the oil more stable, either solid at room temperature or still liquid, but more resistant to oxidation. Without increasing dietary cholesterol or introducing high levels of saturated fat, hydrogenated oils offer more stability for certain food-industry applications, such as frying, baking, and creating a desired texture in pastries, cookies and crackers.

However, recent studies have pointed to the possible negative health effects of trans fatty acids produced during the hydrogenation process, indicating that trans may behave like saturated fat in the body. Nevertheless, the average American only eats a very small amount of trans fat, while consuming a much larger quantity of saturated fat. Trans fat typically represents 2% to 4% of the American diet, while saturated fat represents approximately 12% (Journal of the American Dietetic Association, 1999; 99:166-174). Health advocates such as the American Dietetic Association agree that limiting overall fat intake is the best option.

Background on fats 

The fats found in foods are essential to our diet. Fats supply the body with energy and essential fatty acids, promote the absorption of fat-soluble vitamins and provide insulation. Dietary Reference Intakes (DRIs), issued by the Institute of Medicine of the National Academies in 2002, recommend a range of 20% to 35% of total calories from fat to meet the body’s daily energy and nutritional needs. Nutrition professionals and organizations, such as the American Dietetic Association (ADA), generally suggest that our diets contain no more than 30% of calories from fat. In a 2,000- calorie diet, 30% of calories from fat equates to almost 600 calories, or 66 grams of fat per day.

Many have hypothesized that fats with similar chemical structures may lead to similar health effects in the body. With trans fats, the hydrogen atoms exist on the opposite sides of the carbon chain. This causes the fatty acid to be a straighter chain, more like the straight chain of a saturated fatty acid than like either a monounsaturated or polyunsaturated fatty acid, which have bends in the chain where the carbon atoms have only one hydrogen bonded to them instead of two.

Nature makes most mono- and polyunsaturated fatty acids in the cis form, meaning that the hydrogens that are bonded to the carbon atoms at the point of unsaturation are on the same side of the carbon chain. A small percentage of the fatty acids made in nature are made in the trans form, mainly in meat and dairy products and estimated to be less than 10% of the fatty acids present in these products.

The other major source of trans fatty acids is partially hydrogenated vegetable oil. During the hydrogenation process, when hydrogen is added to make the fatty acids less unsaturated, some of the cis fatty acids will convert to the trans form.

Health issues and

trans fatty acids 

Numerous research and epidemiological studies have been conducted over the past few years to try to determine the impact of trans fatty acids on cholesterol levels and coronary heart disease (CHD). Many of the reports conflict, with some indicating that trans fatty acids do not significantly impact cholesterol levels while others tend to indicate the contrary.

One of the first studies to suggest a possible link between trans fatty acids and risk of heart disease was published in 1992 in the American Journal of Clinical Nutrition (56:1,019-1,024). This study, by Troisi, et al., found a correlation between increased consumption of trans fatty acids and an increase in low-density lipoprotein (LDL; “bad”) cholesterol and decrease in high-density lipoprotein (HDL; “good”) cholesterol. Troisi concluded that this could represent an increased risk of heart attacks.

A review of dietary data from the Nurses’ Health Study, published in 1993 in Lancet (341:581-585), indicated that consumption of trans fatty acids was directly related to risk of CHD.

More recently, a review of a number of studies published in “Fatty Acids in Foods and Their Health Implications” (2nd Ed., 2000) also suggested that high levels of trans fatty acids in the diet appear to raise LDL cholesterol levels and reduce HDL levels, but did not confirm an increase in CHD.

A study on Dutch men found a positive correlation between trans fatty acid intake and the increase in CHD; however, other scientists reviewing the study have questioned whether the results are from the consumption of trans fatty acids or from other forms of fats (Lancet, 2001; 357:746-751, 732-733). The review of the Dutch study further indicates that the results of other epidemiological studies are inconclusive.

In July 2002, the National Academy of Sciences (NAS) issued a report concluding that trans fats boost LDL cholesterol levels more than saturated fat does, and diminish HDL levels. NAS did not set a recommended daily allowance for trans fats or establish safe upper levels, but recommended that people limit their intake as much as possible while eating an overall healthy diet.

The American Dietetic Association (ADA), Chicago, recommends that patients with already high levels of LDL cholesterol limit their intake of foods high in trans fatty acids. Noting the effectiveness of medical nutrition therapy as a means to manage high blood cholesterol and reduce the factors associated with cardiovascular disease, the ADA accordingly developed a protocol for hyperlipidemia (high cholesterol) that includes a lifestyle goal of limiting foods high in trans fat (Journal of the American Dietetic Association, 2002; 102(1):18-20). The studies examined in the ADA protocol were noted for their strong design, though doubts exist about their applicability to the general population, bias and adequacy of sample size in some of the studies. There are also inconsistencies in the results among the studies as a group.

Research at the Dallas-based University of Texas Southwestern Medical Center, as reported in 2000 in the Journal of the American Medical Association (284:2,740-2747), compared the impact of a diet where all of the fat came from butter to one where the source of the fat was tub margarine. When 46 families went on the diet containing tub margarine, 80% of them had lower cholesterol levels than when following the diet containing butter. It should be noted that genetics also appeared to play a role, as parents whose cholesterol levels responded the most significantly to saturated fat also had children whose cholesterol levels responded the most strikingly.

Trans fat intake levels 

The American Heart Association’s Nutrition Committee Dallas, advises that healthy Americans over the age of 2 limit the fat they eat. Specifically, they recommend limiting intake of saturated fat to less than 10% of total calories. Total fat intake should be between 20% and 35% of total calories. In practical terms, if people limit their daily intake of fats and oils to about five to eight teaspoons, the American Heart Association notes they are not likely to get an excess of trans fatty acids. Most popular processed foods offer less than 10 grams of trans fat per serving, suggesting that an overall healthy diet can accommodate a few snack products.

Margarines currently on the market contribute less than 1 gram of trans fat to the daily diet, about 8 calories out of the average 2,000 consumed. Many margarine products, including some tub and most squeeze/liquids, are transfree. As a rule, the softer the margarine product, the fewer trans fatty acids it contains. The trans-fatty-acid levels in partially hydrogenated vegetable shortening used for baking and frying range from 14% to 18%, down from the 25%- plus levels common in previous generations of shortenings.

While most oil that is hydrogenated —canola, soybean and others —will contain trans fat, plain, nonhydrogenated soybean and other oils, such as that used for salad dressing and mayonnaise, do not contain any trans. (Nor do soy and soy-foods in and of themselves contain trans). According to the 2004-05 “National Report on Consumer Attitudes About Nutrition” published by the United Soybean Board (USB), Chesterfield, MO, soybean oil also offers one of the few non-fish sources rich in omega-3 fatty acids essential for various body functions. In a 2004 USB study, 79% of consumers reported that they used vegetable oil or soybean oil most often, and 87% consider soybean oil to be healthy.

While we learn more about the effects of trans fatty acids, the American Dietetic Association’s advice remains to limit total fat intake to no more than 30% of overall calories. Trans fatty acids represent a much-smaller contribution to the overall diet than that of saturated fatty acids. Selecting a wide variety of healthful foods, incorporating fats in the diet in moderation and enjoying regular physical activity will provide Americans with the building blocks toward maintaining good health.

Dedicated to the future of edible oils, the United Soybean Board (USB) has established a core team of exceptional academic and industry professionals who are developing an enhanced soybean that will result in a soybean oil that better meets the needs of food-industry professionals and provides additional health benefits to consumers. A farmer-led organization comprised of 64 farmer-directors, USB oversees the investments of the soybean check-off on behalf of all U.S. soybean farmers. For more information, visit

www.talksoy.com and www.qualisoy.com.