The New Generation of Fake Fats

Meet the New Generation of Fake Fats

By Rebecca Abma

In an effort to rid restaurants and supermarket shelves of harmful trans fats, food manufacturers have found a replacement that may be even worse. Interesterified (IE) fats, chemically modified oils used in baked goods, fried foods, and butter substitutes, appear to have the same harmful effects on cholesterol as trans fats, while also raising blood glucose levels, according to one recent study.

LabelsThe research, published online in Nutrition and Metabolism, followed 30 subjects randomly assigned to rotate through three diets. One diet contained a naturally saturated palm fat, another contained the trans-fat partially hydrogenated soybean oil, and the third used an IE fat.

Subjects followed each diet for four weeks. Researchers found that both the trans fat and the IE fat raised levels of harmful LDL cholesterol and lowered beneficial HDL cholesterol, and also impacted blood glucose levels. While both of the diets high in modified fats were found to raise fasting glucose, the IE plan also suppressed insulin production and raised postprandial (after meals) glucose by 40 percent.

“After one month on the interesterified diet, blood glucose rose from a normal (under 100 mg/dl) fasting to 120 mg/dl levels, which is pre-diabetic levels,” explains study co-author K.C. Hayes, Ph.D., professor of biology in nutrition at Brandeis University. “Granted, for this study we fed subjects a high amount of the worst kind of interesterified fat, but the question was would this extreme fat produce any negative results, and the assumption was it would not. We found a different outcome.” It should also be noted that the study was funded by the palm oil industry, a not disinterested party. But, as Hayes points out, the results could have gone either way for them, and also some palm oil is interesterified.

What are interesterified fats?

One of three fat modification processes — the others are hydrogenation and fractionation — interesterification rearranges fat molecules, making them solid at room temperature while also lowering their melting point. This creates a fat that’s more stable, allowing for high-temperature frying, and less likely to go rancid, giving baked goods a longer shelf life.

For food manufacturers, IE fats offer the benefit of cooking like a trans fat, but without the stigma. As a result, food labels can boast zero trans fats, while still containing fats that are just as harmful, if not more. “Two years ago, everyone thought this was the perfect alternative to trans fats,” explains Christine Gerbstadt, MD, RD, CDE, national spokesperson for the American Dietetic Association. “This new research has food companies scrambling for a replacement.”

What should you look for?

Perhaps the biggest problem with these new bad fats is that there’s virtually no way to know when you’re eating them. No specific labeling exists to alert consumers to the fact that a product contains IE fats. Manufacturers may use the term “interesterified oil” (usually soybean, canola, or palm) on the ingredient list, but it isn’t required. Another term you may see that can mean the same thing is “fully hydrogenated.”

Even more confusing, while IE fats contain saturated fatty acids, they’re not a fully saturated fat, so a label can still make saturated-fat-free claims, while containing these modified oils. “Any time a fat is modified, it won’t be as good for you as a natural fat. The body knows the difference,” Dr. Gerbstadt says. “You want to look for naturally occurring oils that have not been modified, like canola, corn, safflower, sunflower and olive oil.”

The bottom line: “If you’re eating simple, natural foods and not prepackaged foods, restaurant meals and baked goods, you can avoid 99 percent of these fats,” she says. “The more natural something is, the better it will be for you.”

Rebecca Abma is a freelance health writer and a blogger for dLife’s Blogabetes.


Stearic acid-rich interesterified fat and trans-rich fat raise the LDL/HDL ration and glasma glucose relative to palm olein in humans. Nutrition and Metabolism. (Accessed 8/30/07).

International Food Information Council Foundation, Questions and Answers about Interesterified Fats. (Accessed 8/30/07).

ADA Reports. Position of the American Dietetic Association and Dietitians of Canada: Dietary Fatty Acids, from Journal of the American Dietetic Association, 2007, 107:1599-1611. (PDF accessed 8/30/07).

ADA Question of the month: What are interesterified fats? Journal of the American Dietetic Association, 2007, 2007. (Accessed 09/07).

Interesterified Fat: A questionable replacement for trans fat. (Accessed 9/26/07 [at the request of scientist KC Hayes]).

Interviews with KC Hayes, professor at Brandeis University, and Christine Gerbstadt, of the American Dietetic Association.

Reviewed by Susan Weiner, R.D., M.S., C.D.E., C.D.N. 3/08

Last Modified Date: November 27, 2012

All content on is created and reviewed in compliance with our editorial policy.

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