August 11, 2015

expert reaction to review investigating the effects of trans unsaturated fats and saturated fats on health

Exactly how much of different types of nutrients should be part of our diets is the focus of much research, advice and controversy. Publishing in the BMJ, a group has investigated the effects of saturated and unsaturated fats and they report that total trans unsaturated fat intake was associated with increased mortality and death from coronary heart disease, while this was not the case for saturated fats.

Prof. Tom Sanders, Emeritus Professor of Nutrition and Dietetics, King’s College London, said:

“This paper reports associations based on food records of individuals several years prior to the occurrence of cardiovascular disease. This indicates that saturated fatty acids were not related to increased risk but that trans fatty acids were. A note of caution, however, is needed with the interpretation of these data because they show associations that may not be directly causal and may represent other characteristics that influence risk including the overall dietary pattern. In most cases intakes are based on a single dietary assessment at recruitment and make the assumption that neither individual dietary habits nor the composition of the food supply do not changed in the intervening follow-up period; most used memory based methods (most commonly a food frequency questionnaires or a 24 h food recall and rarely 7-day food records). Memory based dietary recall is subject  to substantial bias particularly for food items seen to be good or bad with under-reporting becoming more prevalent among those who are obese. Food frequency questionnaires also underestimate fat intake compared with weighed intake and provide insufficient detail to accurately assess fatty acid intake, particularly with regard to the intake of fats and oils used during food preparation or in commercial food processing.

“Saturated fatty acid intakes have fallen by about 40% since the 1970’s and polyunsaturated fatty acid intakes have increased by 50%. Trans fatty acids are no longer in the UK food chain and have not been for at least 10 years and the main source of trans fatty acids is from fat from ruminant animals (sheep, cattle, goats) and butter. Although, these naturally occurring trans fats are not associated with increased risk of coronary heart disease in this report, they do have the same effects on blood lipids as those derived from industrial trans fatty acids (1).

“Further confusion is added by the divergent relationship of foods rich in saturated fatty acids such as red and processed meat which are associated with increased risk vs. nuts, oily fish and dairy foods which are associated with a lower risk CVD. But it would be foolish to interpret these findings to suggest that it is OK to eat lots of fatty meat, lashings of cream and oodles of butter. Death rates from CVD have fallen in the UK by about 55% since 1997 despite the rise in obesity for reasons that remain uncertain but this may in part be due to changes in the food supply particularly fewer trans and more omega-3 fatty acids which were formerly destroyed by partial hydrogenation.”

Ms Victoria Taylor, Senior Dietitian, British Heart Foundation, said:

“The results of this review support existing guidance to avoid industrially produced trans fats. In the UK, industry action to remove these fats from manufactured foods means that our intakes are already below the recommended maximum 2% of food energy.

“While saturated fats were not robustly associated with total or deaths from CHD, this does not mean we should all go back to eating butter – the studies that this review is based on can’t show cause and effect. Rather, it highlights how difficult it is to understand the true relationship between diet and our health.

“Diets high in saturated fat are linked to raised cholesterol levels, a risk factor for CHD.  But when one nutrient is reduced it will be replaced by another and, depending on what this is, it can have positive or negative health consequences.

“With the recent emphasis that we have had about the direct role of saturated fat on CHD, it’s easy to forget that we need to consider our whole diet to reduce our overall risk. There are many factors which cause CHD and no single food or nutrient is solely responsible for this.

“We will continue to recommend switching saturated fat for unsaturated fat. This is consistent with a traditional Mediterranean style diet, which is a style of eating associated with a lower rate of coronary heart disease.”

‘Intake of saturated and trans unsaturated fatty acids and risk of all cause mortality, cardiovascular disease, and type 2 diabetes: systematic review and meta-analysis of observational studies’ by de Souza et al. published in The BMJ on Tuesday 11th August. 

Declared interests

Prof. Tom Sanders: is a Scientific Governor of the charity British Nutrition Foundation, member of the scientific advisory committee of the Natural Hydration Council (which promotes the drinking of water), and honorary Nutritional Director of the charity HEART UK.  Prof Tom Sanders is now emeritus but when he was doing research at King’ College London, the following applied: Tom does not hold any grants or have any consultancies with companies involved in the production or marketing of sugar-sweetened drinks.  In reference to previous funding to Tom’s institution: £4.5 million was donated to King’s College London by Tate & Lyle in 2006; this funding finished in 2011. This money was given to the College and was in recognition of the discovery of the artificial sweetener sucralose by Prof Hough at the Queen Elizabeth College (QEC), which merged with King’s College London. The Tate & Lyle grant paid for the Clinical Research Centre at St Thomas’ that is run by the Guy’s & St Thomas’ Trust, it was not used to fund research on sugar. Tate & Lyle sold their sugar interests to American Sugar so the brand Tate & Lyle still exists but it is no longer linked to the company Tate & Lyle PLC, which gave the money to King’s College London in 2006.  Tom also used to work for Ajinomoto on aspartame about 8 years ago.

Ms Victoria Taylor: No interests to declare