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New Fat, Old Problem? The Interesterified Fat Controversy

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Starting in 2006, the FDA demanded that products with trans fat list just how much they contain on their nutrition labels, much to the relief of health-conscious consumers—and the chagrin of processed-food purveyors. Scientists scrambled to come up with a replacement for the maligned ingredient, which is linked to a number of health risks but also prolongs the shelf life of crackers, cookies, and other boxed and bagged goods. After all, the public may not want trans fat in their food, but they don’t want Doritos that go stale after a couple of weeks in the supermarket, either.

Enter interesterified fat, a multisyllabic phrase that’s probably as foreign to the average American’s ears as “partially hydrogenated” was twenty years ago. Food companies that once relied on trans fat are turning to this other type of fat for its similar preservative qualities. Now these companies can stamp the front of their packages with “100% Trans Fat Free” labels—but have they simply traded one bad ingredient for another? Is interesterified fat just another ingredient to watch out for?

Science Says …
Like trans fat, interesterified fat is created by turning liquid oils into solidified fats, though the process of doing so is somewhat different. Rather than creating trans-fatty acids, interesterification brings saturated fatty acids, like stearic acid, into the mix to enhance shelf-stabilizing properties. When backlash against trans fat grew in the early 2000s and the public started to scan ingredients lists for it, food producers began experimenting with interesterified fat. Around that same time, researchers commenced testing this replacement ingredient for potential health problems similar to its predecessor’s.

A study published in a 2007 edition of Nutrition and Metabolism was what first caused alarm among consumers and triggered the negative “new trans fat” connotation. Researchers found that a monthlong diet that included interesterified fat lowered good (HDL) cholesterol levels and raised bad (LDL) cholesterol levels, which is also one of trans fat’s unhealthy effects. What’s more, results showed an increase in blood glucose levels by an average of 20 percent and a 22 percent decrease in insulin levels among participants at the end of the study. Both high glucose levels and insufficient insulin to break down glucose are associated with Type 2 diabetes.


Based on this study, one could assume that interesterified fat could be even worse than trans fat, since trans fat doesn’t mess with glucose levels. But neither older nor newer studies have proven the same link between this newer type of fat and adverse physical reactions. A 2000 study published in the Annals of Nutrition and Medicine concluded that there weren’t any “significant differences” between regular butter and butter with interesterified fat when it came to cholesterol levels. A 2005 study at Maastricht University in the Netherlands also showed barely any differences in LDL and HDL concentrations among people given stearic acid (a component of interesterified fat) versus those given other kinds of fatty acids. And a 2007 study published in the American Journal of Clinical Nutrition demonstrated that a three-week diet including stearic acid didn’t negatively affect the participants’ risks for cardiovascular disease or insulin sensitivity.

Proceed with Caution
If there have been so many studies to the contrary, how did the 2007 Nutrition and Metabolism study produce such alarming results? According to researchers from Switzerland’s Nestlé Research Center, who wrote a letter to the editor of Nutrition and Metabolism in 2007 in response to the published study, it wasn’t as controlled as it should’ve been. The letter argues that because the three fats analyzed in the study, including trans fat and interesterified fat, had different properities—varying melting points and amounts of saturated and monounsaturated fats—the results are invalid and further testing is necessary.

With such little evidence to go on, it’s impossible to say whether interesterified fat will eventually prove to be as terrible as trans fat. It took years of testing before we realized that trans fat was contributing greatly to America’s growing health problems. But as of October 2010, the American Heart Association’s stance on interesterified fat is the following: “Given the small study sample, the American Heart Association maintains that the safety profile of interesterified oils and shortenings is not as well understood as that of natural fats and oils. Therefore, additional studies are needed.” In other words, we have to wait and see.

But if you’d rather not take any chances with interesterified fat, be sure to look for it in ingredients labels (check for interesterified fat, as well as stearic acid), and be wary of any products that are suddenly trans fat free. There’s a good chance you’ll find it in frozen foods, baked goods, packaged snacks, and the other usual harbingers of trans fat. Basically, try to avoid heavily processed foods as much as possible. And isn’t that what we should all be doing anyway, regardless of any new ingredient scares?


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