Risks in New Fat May Be Similar to Trans Fat

Shelley Wood

January 19, 2007

January 19, 2007 (Kuala Lumpur, Malaysia) - A new modified fat made through a process called interesterification is shaping up to be the chief contender to substitute for the trans fats being banished from processed foods and restaurants. But researchers who compared the effects of different fats in human diets are warning that interesterified fats may be just as bad as the trans fats they are poised to replace [ 1].

Writing in a paper published online January 15, 2007 in Nutrition & Metabolism, Dr Kalyana Sundram (Malaysian Palm Oil Board, Kuala Lumpur) and colleagues report that compared with a diet high in palm olein (a saturated fat), diets high in either trans fats or interesterified fats significantly raise both LDL/HDL ratio and fasting blood glucose while significantly reducing fasting insulin levels.

The study was supported by the Malaysian Palm Oil Board, which has a major stake in the ongoing fat wars and the hunt for a healthful, stable fat with a long shelf life.

Meddling with Mother Nature's molecules

In an interview with heartwire , senior author on the study, Dr KC Hayes (Brandeis University, Waltham, MA), explained that interesterification grew out of the observation that stearic acid, the fatty acid predominant in chocolate and cocoa butter, unlike other saturated fatty acids, did not appear to raise cholesterol levels. "People got the idea, hmm, let's just take the saturated fatty acid stearic acid out of different oils . . . and put it into an oil like soybean oil. Why not? There's three fatty acids hanging off of soybean oil, why not replace one of the polyunsaturated fatty acids, which makes it an oil, with a neutral saturated fatty acid, and you harden or solidify the product . . . This is the coming rage in replacing trans fats."

But Hayes, who says he's "been looking at fats and oils for 35 years," is concerned about the physiological effects of meddling with fat molecules. His own research has suggested that replacing a polyunsaturated fatty-acid molecule in vegetable oil with stearic acid might pose problems if that stearic acid is placed in the middle fatty-acid position on a fat molecule, since it is not as easily metabolized.

"That's not the way nature set it up. If you look at cocoa butter, which is this nice neutral fat, all of the stearic-acid molecules are on the outside, they are in the one and three positions, they're almost never in the middle. So now when I artificially put my stearic acid in I get about equal amounts [of saturated fatty acid] in positions one, two, and three."

To test their fears about interesterified fats, Hayes and Sundram, with Dr Tilakavati Karupaiah (National University of Malaysia), tested diets rich in the three different fats in 30 volunteers. Each volunteer consumed all three diets, each with strictly controlled total-fat and fatty-acid composition, in random rotation during four-week diet periods.

After four weeks, both the trans-fat and interesterified-fat diets significantly elevated both the LDL/HDL ratio and fasting blood glucose, with the interesterified-fat diet boosting LDL/HDL ratios by almost 20% as compared with the saturated-fat (palm-olein) diet. Fasting insulin at four weeks was 10% lower following the trans-fat diet and 22% lower following the interesterified diet, as compared with the saturated-fat diet. Postprandial glucose on the interesterified diet was also striking higher than on the saturated-fat diet.

Jumping on the next bandwagon?

According to Hayes, interesterified fats are already on the market, being used primarily as a replacement for trans fats in margarines and baked goods. Unlike trans fats, which are required to be listed on labels, interesterified fats are typically listed as "fully hydrogenated" or even as "interesterified fats." Because there has been little public attention being paid to these new manufactured fats, Hayes worries that people may not be aware of the potential harm.

Indeed, whether or not there is harm to be had in interesterified fats remains to be seen.

"To be honest, I can't predict what the implications would be," Hayes said. "We looked at these data and we said, wow, we better tell the world. Let's send it out there and see what other people find, because I'm sure it will stir interest and make people look more carefully at the issue."

Twenty-five years ago, he reminded heartwire , people had concerns about trans fats but assumed that they would never be eaten in large enough quantities to be harmful. History proved otherwise. "I'm not saying interesterified fat is bad stuff for sure, but I am saying, Let's figure out why we saw what we saw, and let's not jump on the next bandwagon without really having a closer look at what the possibilities are."

Hayes is quick to acknowledge the fact that financial support for the study was provided by the Malaysian Palm Oil Board. Sundram is employed by the board and Karupaiah worked with the board as a graduate student. Hayes himself is a member of the Malaysian Palm Oil Advisory Council.

"It's obviously a conflict of interest; I realize that and I'm not trying to disguise or hide that," Hayes said. "But I also think I know more about different kinds of fats, including palm oil, than most people in the world. I see where it's good and where it's weak, and my main goal is to try to get a better fat in the public's hands, in the public's mouth, in the public's bodies."

He continues, "From my perspective, natural fats are still nature's way of doing it. If nature's fat does something you don't like, try blending it with a natural fat that you do like, and that's the way to get to the best solution, as opposed to modifying it, as opposed to saying, we'll trick nature and make this partially hydrogenated or fully hydrogenated."

  1. Sundram K, Karupaiah T, Hayes K. Stearic acid-rich interesterified fat and trans-rich fat raise the LDL/HDL ratio and plasma glucose relative to palm olein in humans. Nutr Metab 2007; doi:10.1186/1743-7075-4-3. Available at: http://www.nutritionandmetabolism.com.

The complete contents of Heart wire , a professional news service of WebMD, can be found at www.theheart.org, a Web site for cardiovascular healthcare professionals.

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