Margarines made from interesterified fat may pose a bigger health risk than margarines made from trans fats

This study was published in Nutrition and Metabolism 2007 Jan 15;4:3

Study title and authors:
Stearic acid-rich interesterified fat and trans-rich fat raise the LDL/HDL ratio and plasma glucose relative to palm olein in humans.

Sundram K, Karupaiah T, Hayes KC.

This study can be accessed at: http://www.ncbi.nlm.nih.gov/pubmed/17224066

Vegetable oils may be converted from liquids to solids by the hydrogenation reaction. Margarines are partially hydrogenated or "hardened" in this way to make them solid at room temperature. Unfortunately this process leads to the formation of trans fats which are implicated in many conditions such as diabetes, cancer heart disease and many other chronic degenerative disorders. Trans fats can also be found in some breakfast cereals, baked goods such as doughnuts and Danish pastry, deep-fried foods like french-fried potatoes, imitation cheese, and confectionary fats.

Because of the unhealthy reputation of trans fats food manufacturers are developing new techniques to "harden" vegetable oils without them containing trans fats. Interesterification is an alternative technique that is used by some margarine manufacturers as part of the process to solidify vegetable oil without producing any trans fats.

In this study dietary trans fats and interesterified fats were compared to a saturated fat for their impact on cholesterol values and blood glucose levels. The study included 30 volunteers whose diets contained a percentage of the various fats for four week periods.

The fats in each diet were based on:
(i) Palm olein (saturated fat diet).
(ii) Partially hydrogenated soybean oil (trans fat diet).
(iii) Fully hydrogenated fat blend subjected to chemical interesterification (interesterified fat).

The study found:
(a) Compared to the saturated fat diet, levels of the beneficial high density lipoprotein (HDL) cholesterol were 7.6% lower in those on the trans fat diet.
(b) Compared to the saturated fat diet, levels of the beneficial high density lipoprotein (HDL) cholesterol were 9.1% lower in those on the interesterified fat diet.
(c) Compared to the saturated fat diet, levels of blood glucose rose by a harmful 5.1% in those on the trans fat diet.
(d) Compared to the saturated fat diet, levels of blood glucose rose by a harmful 18.7% in those on the interesterified fat diet.

The results of the study show that interesterified fat lowers the levels of the beneficial high density lipoprotein (HDL) cholesterol even more than trans fat.

Interesterified fat also raised blood glucose levels significantly higher than trans fat which strongly suggests that interesterified fats found in margarines and processed foods could lead to an even higher risk of diabetes than the trans fat containing foods.

Links to other studies:
Is interesterified fat as bad as trans-fat?
Interestification of fats may cause heart disease