Interesterified Palm Olein (IEPalm) and Interesterified Stearic Acid-Rich Fat Blend (IEStear) Have No Adverse Effects on Insulin Resistance: A Randomized Control Trial

Chemically-interesterified (CIE) fats are trans-fat free and are increasingly being used as an alternative to hydrogenated oils for food manufacturing industries to optimize their products' characteristics and nutrient compositions. The metabolic effects of CIE fats on insulin activity, lipids, and adiposity in humans are not well established. We investigated the effects of CIE fats rich in palmitic (C16:0, IEPalm) and stearic (C18:0, IEStear) acids on insulin resistance, serum lipids, apolipoprotein concentrations, and adiposity, using C16:0-rich natural palm olein (NatPO) as the control. We designed a parallel, double-blind clinical trial. Three test fats were used to prepare daily snacks for consumption with a standard background diet over a period of 8 weeks by three groups of a total of 85 healthy, overweight adult volunteers. We measured the outcome variables at weeks 0, 6, and at the endpoint of 8. After 8 weeks, there was no significant difference in surrogate biomarkers of insulin resistance in any of the IE fat diets (IEPalm and IEStear) compared to the NatPO diet. The change in serum triacylglycerol concentrations was significantly lower with the IEStear diet, and the changes in serum leptin and body fat percentages were significantly lower in the NatPO-diet compared to the IEPalm diet. We conclude that diets containing C16:0 and C18:0-rich CIE fats do not affect markers of insulin resistance compared to a natural C16:0-rich fat (NatPO) diet. Higher amounts of saturated fatty acids (SFAs) and longer chain SFAs situated at the sn-1,3 position of the triacylglycerol (TAG) backbones resulted in less weight gain and lower changes in body fat percentage and leptin concentration to those observed in NatPO and IEStear.

Effects of Plant Oil Interesterified Triacylglycerols on Lipemia and Human Health

The position of the fatty acids (sn-1, sn-2 and sn-3) (stereospecific numbering (sn)) in triacylglycerol (TAG) molecules produces a characteristic stereospecificity that defines the physical properties of the fats and influences their absorption, metabolism and uptake into tissues. Fat interesterification is a process that implies a positional distribution of fatty acids (FAs) within the TAG molecules, generating new TAG species, without affecting the FA cis-trans natural balance. The interesterified (IE) fats, frequently used in the food industry comprise fats that are rich in long-chain saturated FAs, such as palmitic acid (16:0) and stearic acid (18:0). Within the interesterified fats, a critical role is played by FA occupying the sn-2 position; in fact, the presence of an unsaturated FA in this specific position influences early metabolic processing and postprandial clearance that in turn could induce atherogenesis and thrombogenesis events. Here, we provide an overview on the role of TAG structures and interesterified palmitic and stearic acid-rich fats on fasting and postprandial lipemia, focusing our attention on their physical properties and their effects on human health.

What are interesterified fats and should we be worried about them in our diet?

Interesterified (IE) fats are used in a wide range of food products and were introduced as a replacement for trans fats, which are known to be detrimental to cardiovascular health. However, the effects of interesterification on metabolism and subsequent effects on cardiovascular health are not understood and previous studies have seldom investigated industrially-relevant IE fats. No legislation currently exists regarding the labelling of IE fats in food products and therefore estimates of average consumption rates in the UK population are currently unavailable. In order to meet the urgent need for a systematic investigation of the health effects of consumer-relevant IE fats, it is essential to estimate current IE fat intakes and to investigate biological mechanisms that might mediate acute and chronic cardiometabolic effects of commercially relevant IE fats.

The Increasing Use of Interesterified Lipids in the Food Supply and Their Effects on Health Parameters

A variety of modified fats that provide different functionalities are used in processed foods to optimize product characteristics and nutrient composition. Partial hydrogenation results in the formation of trans FAs (TFAs) and was one of the most widely used modification processes of fats and oils. However, the negative effects of commercially produced TFAs on serum lipoproteins and risk for cardiovascular disease resulted in the Institute of Medicine and the 2010 US Dietary Guidelines for Americans both recommending that TFA intake be as low as possible. After its tentative 2013 determination that use of partially hydrogenated oils is not generally regarded as safe, the FDA released its final determination of the same in 2015. Many food technologists have turned to interesterified fat as a replacement. Interesterification rearranges FAs within and between a triglyceride molecule by use of either a chemical catalyst or an enzyme. Although there is clear utility of interesterified fats for retaining functional properties of food, the nutrition and health implications of long-term interesterified fat consumption are less well understood. The Technical Committee on Dietary Lipids of the North American Branch of the International Life Sciences Institute sponsored a workshop to discuss the health effects of interesterified fats, identify research needs, and outline considerations for the design of future studies. The consensus was that although interesterified fat production is a feasible and economically viable solution for replacing dietary TFAs, outstanding questions must be answered regarding the effects of interesterification on modifying certain aspects of lipid and glucose metabolism, inflammatory responses, hemostatic parameters, and satiety.