The health impact of industrial interesterification of dietary fats

Dietary fat forms an important part of our diet, however, trans and saturated fats are associated with increased risk of cardiovascular disease. Certain foods, such as spreads and bakery products need solid fat in order to produce desirable taste and texture. However, the health risks associated with trans and saturated fats mean that different approaches to create solid fats are required. One method is to incorporate interesterified fats into foods. Interesterification is an industrial process used for blends of vegetable oils that changes the structure of the fat without changing the overall fatty acid composition in the total fat. This results in a harder fat than the original structure of the vegetable oils, which can be used in place of butter and lard (both high in saturated fat) and partially hydrogenated fats (high in trans fat).

Despite the global use of interesterified fats in a wide range of foods, their health effects have not been investigated. Initial research from our group found that one of the most commonly consumed interesterified fats leads to differences in blood fat levels after consumption compared to the same fat that has not been interesterified. Large rises in blood fats after meals are an important risk factor for cardiovascular disease. This project will investigate the cardiovascular health effects of typically consumed interesterified fats to address this crucial gap in scientific evidence. The project is organised into 3 objectives. Firstly, we will use an existing UK database of dietary intakes in a large, nationally representative study population, together with information on interesterified fat contents of foods provided by a leading food company, to estimate dietary intakes of interesterified fats in the UK. We will use this information to predict what would happen to blood fats if current dietary intakes of interesterified fats were replaced by fats like butter and lard. This will provide the first ever data set on the potential public health impact of including these fats in the UK food supply. We will then undertake a detailed human study to assess the effects of the most commonly consumed interesterified fat, compared to the non-interesterified equivalent fat, and the vegetable oil that the interesterified fat is normally blended with. We will explore the biological reasons why the amount of fat in the blood may differ after consuming these fats. Cutting edge methods will be employed to assess differences in gut handling, fat absorption and the fate of the fats once they are in the blood stream. Finally, we will run a second human study to determine whether blends of different proportions of these fats, i.e. the proportions that are most commonly consumed in products such as "healthier" spreads and bakery fats, have any effects on the factors that influence risk of cardiovascular disease, compared to a control oil that does not contain any interesterified fat, and a second control fat that is entirely interesterified fat. Model digestion methods will be used to understand the mechanisms underpinning the results of the human studies.

The overall aim is to gain a fuller understanding of what contribution these interesterified fats make to the UK diet, why they might lead to differences in blood fat levels and whether this influences known risk factors for cardiovascular disease. Our hypothesis is that the overall effect of consuming these fats, in the quantities available in commercial food products, will reduce cardiovascular disease risk when compared to alternative fats with the same functional properties. The study's findings will provide valuable information to the food industry and will arm nutritionists, dietitians, other health professionals and government policy makers with robust scientific evidence for the potential health impact of consuming interesterified fats which will help, in the longer term, formulate dietary advice for the general public.

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.