We’ve heard about trans fat for years. Research and health professional communities have long investigated potential uses and health impacts of trans fat in food. However, according to the IFIC Foundation Food & Health Survey, consumer awareness of trans fat has peaked only in the last few years, with awareness increasing significantly over the last several years.
In 2003, the U.S. Food & Drug Administration (FDA) issued a regulation to require mandatory labeling of trans fat in foods and beverages within three years. In 2006, a line was included on the Nutrition Facts Panel indicating trans fat content. In 2010, the Dietary Guidelines for Americans advised consumers to “keep trans fatty acid consumption as low as possible by limiting foods that contain synthetic sources of trans fats, such as partially hydrogenated oils, and by limiting other solid fats.”
In November 2013, the FDA issued a Federal Register notice with a preliminary determination that partially hydrogenated oils (PHO), the largest source of trans fat in American diets, would no longer be generally recognized as safe (GRAS). A public comment period ensued and recently closed on March 8, 2014.
Dr. Ronald Mensink
The case of PHOs and trans fat, however, is not “closed.” Consumers and health professionals still have many questions regarding the safety and use of PHOs in food production and potential health implications of consuming trans fat, such as PHOs. With that in mind, we recently interviewed Dr. Ronald Mensink, a leading global researcher and expert in the field of human nutrition. Dr. Mensink works in the Department of Human Biology at Maastricht University in the Netherlands, where he is also a professor of Molecular Nutrition with an emphasis on lipid metabolism and leader of Research line 1 “The Metabolic Syndrome” from NUTRIM (School for Nutrition, Toxicology and Metabolism). With such an impressive background, you can expect his insights trans-lated into one tough lesson in lipid science and oil hydrogenation!
FI: Let’s start with the basics. When was the hydrogenation process (of oils) first developed and why?
RM: Around 1900, Wilhelm Normann (a German chemist) patented a process to hydrogenate oils. This made it possible to convert a liquid vegetable oil into a more solid fat. At that time, the potential benefits of hydrogenating oils were enormous. The hydrogenated fat could be used as the basis for the production of “margarine,” which was very much needed at the time due to a shortage of butterfat on the market. Hydrogenation also made it possible to find a more affordable use for vegetable oils, which were less expensive than animal fats.
FI: What is the difference between saturated and unsaturated fatty acids?
RM: All fats and oils are composed of different fatty acids, which can be saturated or unsaturated. An unsaturated fatty acid has at least one double bond. In general, this is a so-called cis double bond, which means that the fatty-acid molecule has a “kink.” (See diagram at left.) As a result, these cis-unsaturated fatty acids have a low melting point and are liquid at room temperature.
FI: And what is the difference between partially and fully hydrogenated oils?
RM: Vegetable oils that contain oleic acid, linoleic acid, and alpha-linolenic acid are used for hydrogenation. These three unsaturated fatty acids have one, two and three cis double bonds, respectively. If you fully hydrogenate these three fatty acids, they will all be converted into stearic acid, which is a saturated fatty acid commonly found in our diet and also in many fats and oils.
During partial hydrogenation, the cis double bond can be converted into a trans double bond. Thus, in contrast to a partially hydrogenated oil, the level of trans fatty acids in fully hydrogenated oils is much lower. Some trans fatty acids, however, are always present, whether they are a result of hydrogenation or other processes needed to make the oil acceptable for human consumption.
FI: What is trans fat?
RM: When a cis-unsaturated fatty acid has a trans double bond (i.e. “trans fat”), it creates trans fat. The molecule is more stretched (like that of a saturated fatty acid) and its melting point is higher.
FI: Are all trans fats the same?
RM: No. There are different forms of trans fatty acids in our diets. Most trans fatty acids have 18 carbon atoms and one double bond. However, some trans fatty acids have more double bonds, or 16 carbon atoms and one double bond.
FI: What are the sources of trans fats typically found in our diet?
RM: There are two sources of trans fat in our diets. One source is from hydrogenated oils. The other source is meat and dairy products from ruminating animals (e.g. cows, goats, and sheep). Trans fat occurs in the products of these animals through biohydrogenation of unsaturated fatty acids by rumen bacteria. The resulting trans fatty acids are sometimes called “natural” trans fats; however, it is unclear whether “natural” sources of trans fat have different metabolic effects than hydrogenated oils.
FI: Are there health risks associated with consuming partially hydrogenated oils and/or trans fats?
RM: Many research papers suggest adverse health effects of trans fatty acid consumption, but not all results are consistent. A very consistent finding, however, is the positive relationship between trans fatty acid intake and the risk of developing cardiovascular disease (CVD). These studies come from many different countries, using different cohorts and methods to estimate trans fatty acid intake. Many of these studies were initiated after we found that increasing intake of trans fat (18-carbon) from hydrogenated fats at the expense of oleic acid increased the concentration of the atherogenic LDL cholesterol, while at the same time decreasing HDL cholesterol.*
These effects have since been confirmed repeatedly and also at lower (more realistic) intakes. Thus, intervention studies and prospective epidemiological studies are very much in agreement and show negative effects of trans fats on risk factors for cardiovascular disease and on cardiovascular disease itself.
Partially hydrogenated fats may also negatively affect other risk markers for cardiovascular disease, but those results are more controversial. However, it should be noted that some studies suggesting that high plasma levels of trans fatty acids with 16 carbon atoms may be associated with some positive health effects, but this requires further study.
FI: How has trans fat consumption (from both natural and hydrogenated sources) changed in recent decades?
RM: Survey data have shown that consumption of trans fat is decreasing. Although it is difficult to have good quantitative estimates for intakes due to wide variations between subjects and even between brands of the same type of food product, intake of naturally occurring trans fat is low and the intake of hydrogenated fats is decreasing. At the current time, I wouldn’t be surprised if intake from both sources is about equal.
FI: At our current level of consumption level, what does research indicate about trans fats’ impact on our health?
RM: A difficult question to answer. In general, you can say “the less, the better,” but the impact on health also depends on what replaces trans fat in the diet.
FI: Some of your research has shown that it may be more beneficial to consume some trans fat in your diet as compared to none. Why might this be?
RM: The health effects of fats and oils should be the driving force when formulating food products. However, in food preparations, you also use the taste and functional characteristics of a fat. You cannot simply exchange one oil or fat for another without affecting the characteristics of the product.
In one of our studies, we tested two semi-liquid fats with similar functional characteristics, but with different fatty acid compositions. One fat consisted of 4.5% trans fatty acids, but was rich in cis-monounsaturated fatty acids (oleic acid). The other fat consisted of only 1% trans fatty acids, but was rich in saturated fatty acids. The total diets provided less than 0.7% of energy from trans fatty acids, but the health effects of the semi-liquid fat with the highest level of trans fatty acids were more favorable on LDL cholesterol and the total to HDL cholesterol ratio, but less favorable on HDL cholesterol.
Of course, this does not mean that there is no need to reduce the intake of trans fat, but that we should not focus on trans fatty acids alone.
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*Low HDL cholesterol (less than 40 mg/dL for men, less than 50 mg/dL for women) is associated with a higher risk of heart disease. An HDL of 60 mg/dL and above is considered protective against heart disease. (American Heart Association, 2013)