The health impact of industrial interesterification of dietary fats

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Interesterification (IE) of dietary fats results in the re-esterification of fatty acids across the sn-1, sn-2 and sn-3 positions of the glycerol backbone of triacylglycerol molecules, thereby changing the proportion of saturated fatty acids in the sn-2 position and the solid fat content of the blend. It is now extensively used by the food industry, in place of trans fats, to create fats with desirable functional characteristics. Research into the health effects of IE fats has been sparse and has focused primarily on fats that are rarely used commercially. This project will investigate the potential cardiovascular health effects of commonly consumed IE fats by: 1) combining observational data from the UK National Diet and Nutrition Survey and technical data from the UK's leading IE fat supplier to estimate UK dietary consumption, and to provide model estimates of predicted cardiovascular health effects of their consumption vs. application-appropriate alternatives; 2) investigating the effect of interesterification of a typical blend of palm stearin/palm kernel (PSt/PK) fat, compared to a non-interesterified equivalent, on digestion and postprandial lipid metabolism, using in vivo postprandial studies (single-meal randomised crossover study), stable isotope tracer techniques and in vitro gut modelling; 3) evaluating the acute cardio-metabolic health effects of the different ratios of the most commonly consumed blend ratios compared to reference fats (100% IE PSt/PK and 100% vegetable oil), in a sequential-meal, randomised, crossover, double-blind design. These studies are also designed to unravel the molecular (e.g. sn-2 composition) and physico-chemical (e.g. solid fat content) mechanisms underpinning any differential postprandial lipaemic responses. Outcomes will facilitate an understanding of prevalence of IE fats in the UK diet and potential cardio-metabolic health effects, arming the food industry with knowledge that can be used to maximise health benefits.

Incorporating interesterified (IE) fats into certain foods yields desirable functional characteristics whilst negating the need for trans fats and reducing the saturated fatty acid (SFA) content by about 10-20%, thereby forming a functional fat with improved predicted health benefits. IE fat blends are estimated to supply between 4-10 % of average daily energy intake (unpublished industry sources), thus there is a pressing need to understand their health effects. Systematically assessing current IE fat intakes in the UK will provide the food industry with valuable data for estimates of typical dietary intakes in the general population and subgroups (sexes, age groups and socio-economic groups etc.). This data, together with model estimates of changes in blood lipids as a result of replacing IE fats with functional alternatives such as traditional fats (butter, lard), or trans fats (now abandoned by the UK food industry due to deleterious health effects), will provide the government with essential public nutrition information on national trends in dietary intakes and potential health implications.

A detailed examination of potential physiological adaptations occurring during digestion, absorption and metabolism of the most commonly consumed IE palm-derived fat blend will bridge the knowledge gap in this neglected area of food and health research. Results will significantly advance the knowledge of food scientists working in the food industry and academia at an international level as to the biological consequences of interesterification. A clearer understanding of the gastrointestinal and metabolic fate of the most commonly consumed IE fat may also inform the design of other IE fats that might be developed in the future for broader food applications.

A full comprehension of the effects of consuming IE fat blends on lipoprotein metabolism, inflammation and endothelial function will help to ensure a safe and sustainable supply of fat with desirable functional characteristics. The outcomes of these studies will contribute a robust body of evidence to support potential claims that could be made by manufacturers regarding the physiological effects of IE fats compared to other application-appropriate fats with the same functionality. This will ultimately contribute to the development of other new products containing variations of IE fat blends which may help to reduce the risk of developing cardiovascular/metabolic disease. In the longer term the study will improve marketing of IE fat-containing products with information about health effects compared to earlier-generation fats (e.g. margarine) with similar functionality, and will lead to a deeper understanding of how delivering different combinations of IE fats with vegetable oils, such as rapeseed and linseed can affect health outcomes.

In addition to the distinct impact on the food industry, and the clear benefit to authorities who advise and formulate nutrition policy, the other direct beneficiary group is the UK population. With an ageing, largely sedentary society and alarming forecasts for trends in type 2 diabetes (T2D), evidence on cardio-metabolic health effects of widely consumed food ingredients such as IE fats will be relevant to most of the population. Treating CVD and T2D currently costs the NHS around £20bn p.a. (approx. 20 % of total budget) and CVD is responsible for over a quarter of all deaths in the UK. The groundswell of popular opinion that traditional fats, such as butter, are healthier than spreads will be tempered by the provision of authoritative consumer information on the influence of IE fat-containing spreads/cooking fats on health outcomes as a specific output of this project. This will empower the general public to make an informed choice when purchasing fats for home-baking, cooking and general consumption. In addition, consumers will benefit from a wider choice of high quality, desirable foods with more clearly defined health benefits.