Since trans fat labeling became mandatory on Nutrition Facts panels in 2006, food manufacturers have been working to get sources of artificial trans fat (which is created through a chemical process known as “partial hydrogenation”) out of their products.
And since New York City’s Board of Health voted to ban trans fats from the city’s restaurants beginning this summer, restaurants there and elsewhere in the United States have also been scurrying to find replacement fats for their cooking and baking needs. (See our previous posts on this topic, “Nation’s First Trans Fat Ban Approved” and “Proposed Trans Fat Ban and Calorie Listing Sparks Debate.”)
Trans fat consumption, in addition to raising LDL (or “bad”) cholesterol, has been shown to lower levels of HDL (or “good”) cholesterol. These actions can raise a person’s risk of developing heart disease.
Unfortunately, a recent study found that “interestified” fat, a type of fat that some manufacturers are already using as a replacement for partially hydrogenated fat in foods, may have its own health risks.
The study, which was published in the January 15 issue of the journal Nutrition & Metabolism, was designed to look at the effects of three different “test fats” on people’s cholesterol and blood glucose levels. A group of 30 volunteers were fed identical-looking diets that contained a specific amount of either palm olein (made from palm oil, which is naturally rich in saturated fat), partially hydrogenated soybean oil (rich in trans fat), or interestified soybean oil. All volunteers participated in all three diets over separate four-week periods.
The researchers found that the diet rich in partially hydrogenated fat and the diet rich in interestified fat both lowered HDL cholesterol levels to a similar extent compared to the diet rich in saturated fat. However, the diet high in interestified fat also raised fasting blood glucose levels significantly more than the other two diets for every participant in the study. It appears that this effect may have been due to the interestified fat’s effect on the volunteers’ insulin levels; both the interestified-fat and the partially-hydrogenated–fat diets were found to lower insulin levels in the study participants, but the interestified-fat diet lowered insulin levels twice as much as the partially-hydrogenated–fat diet did.
The study’s participants did not have diabetes, so whether interestified fat would have the same effect on the blood glucose levels of people with diabetes is unclear. However, the researchers expressed concern because the interestified fat had such a significant effect on the study participants’ blood glucose and cholesterol levels after just four weeks, and also because some food manufacturers are already replacing partially hydrogenated fats in their products with interestified fats.
Interestification is a multistep process that begins with the full hydrogenation (rather than partial hydrogenation) of fat molecules. Full hydrogenation hardens liquid oils, turning them into saturated fats. These fats are then combined with liquid oils through further chemical processing, resulting in interestified fats.
This study highlights the importance of looking beyond “Trans Fat Free” claims and even the Nutrition Facts panels on packaged foods. To find out if a product contains interestified fats, check the ingredients list on the package to see if it contains “fully hydrogenated” oils.