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Translating Trans Fat

by Carole Conn, PhD, RD on Feb 01, 2004

Help your clients make choices that will limit their intakes of unhealthy trans fat.

Nutrition experts have long been urging consumers to cut down on their fat intake. Recently, a lot of attention has centered on a harmful type of fat known as trans fat. Problem is, trans fat content is not currently identified on most food labels. To give consumers benefit of this important information, on July 11, 2003, the U.S. Food and Drug Administration (FDA) issued a new rule requiring manufacturers of conventional foods and some dietary supplements to list trans fat on food labels; manufacturers have until 2006 to comply with this new rule.

While the new labels will provide essential information to assist those trying to make better food choices, many consumers (and some fitness professionals!) are still in the dark about just what trans fat is and why this new ruling was necessary. To help you respond to questions from your clients, this article provides an overview of trans fat; identifies some common food sources with high trans fat content; and describes the scientific evidence that suggests that a diet high in trans fat may be harmful to health.

Defining Trans Fat

Dietary fat is largely made up of fatty acids. There are two main types of fatty acids: saturated fatty acids (SFAs) and unsaturated fatty acids (UFAs). Although both types are present in fat, specific dietary fats are typically categorized based on the predominant fat. Generally speaking, saturated fats (i.e., dietary fats made up chiefly of SFAs) are considered the least healthful types of fat, owing to their negative effects on serum cholesterol levels.

Most unsaturated fats are considered healthier than saturated fats; these healthier alternatives are chiefly made up of cis fatty acids, which have a chemical formation that functions optimally in the body. However, some unsaturated fats are primarily made up of trans fatty acids, which have a chemical formation that is more similar to that of a saturated fat.

Recent studies have indicated that unsaturated fat containing trans fatty acids—known as trans fat—may be just as harmful to health as saturated fat. Trans fatty acids have been shown to interfere with the way healthy cis fatty acids work in the body, impairing vital functions such as immunity, cell membrane development and enzyme activity (Sébédio & Chardigny 1998; Groff & Gropper 2000; Calder et al. 1994). Trans fatty acids can affect the function of two of the most important cis trans fatty acids, linoleic acid and linolenic acid, which are considered essential since they can be obtained only through dietary sources, like plant oils.

The new label information will specify the number of grams of unsaturated trans fat—not the cis fat—that is part of the total fat content of any given food. The trans fat entry will appear on the new labels directly under the entry for saturated fat. For details on what products will list, see “The New Trans Fat Labeling Law” on this page.

Common Food Sources of Trans Fatty Acids

Trans fatty acids are found in both animal and plant sources in our diets. Bacteria in the digestive tract of some animals, such as cows, sheep and goats, actually produce trans fatty acids during digestion. About 3 to 5 percent of the unsaturated fatty acids found in milk and meat derived from these animals are in the trans formation (Stender et al. 1995). The actual amount varies, depending on what the animals are fed (Bauman et al. 2000).

Trace amounts of trans fatty acids occur naturally in some plant sources, such as certain vegetables (Ackman & Mag 1998). Although small quantities of trans fatty acids can form during the production of vegetable oils, most salad and fish oils contain the healthier cis formation. However, plant oils are often processed and partially solidified to create shortening and margarine (Alexander 1981). In a process known as hydrogenation, the oils are heated to a very high temperature in the presence of hydrogen, causing them to harden at room temperature (Ackman & Mag 1998). During the hydrogenation process, some of the unsaturated cis fatty acids become saturated fatty acids and some are transformed into trans fatty acids. The longer the oil is hydrogenated, the more saturated and solid it becomes. For example, stick margarine is harder than tub margarine because it has undergone a longer hydrogenation process. As a result, stick margarine contains more saturated fat and trans fat than tub margarine.

Manufacturers rely on hydrogenation to prevent oils from becoming rancid, thus improving products’ shelf life. In addition, oils that are solid at room temperature produce better textures for processed baked products, such as cakes and pastries. It is estimated that 80 to 90 percent of the intake of trans fatty acids in the average American’s diet comes from eating these partially hydrogenated fats as table spreads and as fried or baked products, especially snack foods (American Society for Clinical Nutrition & American Institute of Nutrition 1996).

You might be surprised at the number of common foods that are high in trans fat (see “Comparing Fat Contents” below) and how easy it is to consume this type of fat unwittingly over the course of a day. Look at how quickly trans fat adds up when you consume these ordinary items:

Breakfast: 2 slices of toasted bread made with partially hydrogenated vegetable oil (~ 0.4 gram [g] trans fat) spread with 2 teaspoons of stick margarine (~ 2.5 g trans fat)

Morning Snack: coffee and one donut (~ 3 g trans fat)

Lunch: a cup of soup with 8 saltine crackers (~ 1 g trans fat)

Afternoon Snack: cheese, grapes and a handful of snack crackers (~ 2 g trans fat)

Dinner: a small hamburger with a bun (~ 0.5 g trans fat) and a small order of French fries (~ 3 g trans fat)

This modest menu contains a whopping 12.4 g of trans fat for the day! To put this into perspective, remember that for someone eating approximately 1,800 calories a day, 12.4 g of trans fat amounts to approximately 6 percent of his or her total daily calories.

Weighing In With the Research

The primary reason food labels are being revised is because of the body of scientific research that links trans fat intake to an increased risk for cardiovascular disease. Specifically, trans fat has been shown to increase low-density lipoprotein (LDL) levels and decrease high-density lipoprotein (HDL) levels (Ascherio & Willett 1997). In fact, one meta-analysis of 60 controlled trials concluded that replacing dietary trans fatty acids with unsaturated cis fatty acids from unhydrogenated oils is the most effective way to improve blood lipid risk factors (Mensink et al. 2003).

Other, less conclusive studies have suggested that trans fat intake has a negative impact on fetal brain development (Larque et al. 2000) and immune responses (Han et al. 2002). Trans fat has also been linked to certain cancers (Slattery et al. 2001; Zhang et al. 1999), although the mechanisms remain unclear.

The relationship between trans fat intake and the development of obesity and diabetes is also still being determined. A recent study did note a correlation between increased waist circumference (an indicator of upper-body obesity) and calorie intake from trans fat (Koh-Banerjee et al. 2003). And a large epidemiological study of women found that a slight increase in trans fat consumption increased the risk of developing diabetes (Hu, van Dam & Liu 2001).

The new requirement to list trans fat on food labels represents a shift in thinking among nutrition experts due to new evidence about the harmful effects of partially hydrogenated oils. As recently as the 1960s and 1970s, foods made from hydrogenated vegetable oils were viewed as healthy alternatives to butter and lard. Products like margarine were lauded because they contained no cholesterol and, compared to butter and lard, had less saturated fat and led to lower total serum cholesterol levels (Lichtenstein 2000). Additionally, unsaturated fatty acids were thought to function in the body in the same way, regardless of whether they were in the cis or trans formation.

It wasn’t until the 1990s, once scientists began examining LDL and HDL cholesterol levels separately (Mensink & Katan 1990), that substantial evidence began to accumulate about the harmful effects that the trans fatty acids in hydrogenated oils have on cardiovascular disease. Now that we know far more about “good” (HDL) and “bad” (LDL) cholesterol, we will undoubtedly learn more about how trans fatty acids function in the body and how they affect overall health. In fact, further research may even determine that some trans fatty acids have a positive effect on health. For example, recent studies found that intake of a particular trans fatty acid actually prevented obesity and cancer in animal subjects (Belury 2002). But, for now at least, the overwhelming body of scientific literature supports the recommendation to reduce intake of trans fat to maintain optimal health.

Reducing Trans Fat Intake

Here are several ways your clients can decrease their daily intake of trans fat, starting right now:

1. Lower total fat intake by choosing a diet rich in fruits, vegetables, legumes, low-fat dairy products and baked/broiled lean meats and fish. It is important to note that most people actually eat much more saturated fat each day (an average of 10 to 19 percent of their energy) than trans fat. According to the FDA, the average daily U.S. consumption of trans fat ranges from 1.3 g to 12.8 g—making up about 3 percent of total calories (Federal Register 2003). Limiting total fat intake will decrease the amount of unhealthy saturated and trans fat in the diet. For a look at different types of fat in some common foods, see “Comparing Fat Contents” on page 37.

2. Replace “hard” fats like margarine with salad oils, such as olive oil and canola oil. For instance, bake your own breads, cakes and pancakes using liquid vegetable oil instead of shortening. Dip your bread in olive oil instead of spreading it with butter or stick margarine, or use a trans-fat-free margarine, peanut butter or other nut butter.

3. Whenever possible, avoid deep-fried foods, especially when dining out at restaurants. French fries and donuts are particularly loaded with trans fat. Remember that even if a menu boasts, “We cook in vegetable oil,” that oil could very well be hydrogenated and contain trans fat!

4. Check food labels for the term “partially hydrogenated” vegetable (e.g., soybean, corn, cottonseed, peanut) oil. The higher such an oil appears on the list of ingredients, the more trans fat is likely to be in the food. Again, the fact that the package boasts “No cholesterol, containing all vegetable oil” doesn’t mean the product is free of trans fat.

5. Become familiar with the categories of store-bought foods likely to be made with partially hydrogenated oils. When shopping, take along a list of foods to avoid, shown in “Trans Fat Culprits” above.

The Future of Trans Fat

While the new food labels will not be mandatory until 2006, there have already been some encouraging developments in the food industry. For example, some manufacturers are already reformulating the way they process oils to decrease the amount of trans fatty acids formed (Ackman & Mag 1998). As a result, savvy consumers can now readily find trans-fat-free tub margarines at their local supermarket. It is also expected that raising consumer awareness of total fat intake will ultimately lower consumption of harmful saturated and trans fats. In turn, cholesterol levels will fall and the risk of serious disease decline for many of our clients.


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IDEA Health Fitness Source, Volume 2005, Issue 2

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About the Author

Carole Conn, PhD, RD IDEA Author/Presenter

Carole A. Conn, PhD, RD, FACSM, teaches nutrition science at the University of New Mexico in Albuquerque and lectures internationally on nutrition, exercise and health topics. She was awarded an Outst...