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Health and Disease
Summary special session at the Euro Fed Lipid congress
"Health effects of saturated fatty acids (SAFA) and its possible replacements"
September 20, 2011
These two sessions, chaired by Pramod Khosla (Wayne State University, USA) and Peter Zock (Unilever R&D, The Netherlands) were established in order to present the different scientific views on the validity of the worldwide recommendations to reduce the amount of dietary saturated fatty acids (SAFA). Eight scientists were invited to present their views and this was followed by a panel discussion.
The first speaker was professor Ronald Mensink (Maastricht University, The Netherlands). He started with a general overview on the role of dietary SAFA on blood lipids. He emphasized that health effects of any nutrient should always be defined against the nutrient it replaces, since it is not possible to discuss the effects of any of the macronutrients in isolation. From a historical point of view the health effects of SAFA have been evaluated by comparing them to iso-energetic amounts of carbohydrates. Coronary heart disease risk is determined by measuring blood lipids like LDL, HDL, their ratios and triglyceride concentrations. For example, the ratio of total to HDL cholesterol is positively related to the risk of coronary heart disease. Based on consistent evidence from human studies, professor Mensink showed that SAFA intake has no effects on the total:HDL cholesterol ratio compared with carbohydrates and replacement of SAFA by unsaturated fatty acids will be beneficial. However, individual SAFA have different effects on these blood lipids: lauric acid is more favourable than carbohydrates, whereas stearic acid is neutral. Results from studies on other markers not related to the lipid pathway (e.g. postprandial glucose metabolism, inflammatory markers) are scarce and mixed. He concluded that overall an intake of SAFA in line with the current dietary recommendations is advisable.
Professor Julie Lovegrove (University of Reading, UK) presented the results of 3 intervention trials in which both the quality and quantity of fat and carbohydrates were studied in relation to cardiometabolic risk. She mentioned that people suffering from metabolic syndrome have a 2-3 times higher risk of developing cardiovascular diseases and a 5-6 times higher risk for diabetes. The first trial presented (the RISCK study), was performed at 5 centres within the UK and consisted of an intervention of 24 weeks with 5 different diets. The control diet was a diet with a high SAFA content and high glycemic index and in the test diets SAFA were replaced by either mono unsaturated fatty acids or carbohydrates, and differed also in glycemic index (high and low). The second study presented (the LIPgene study) was a pan European intervention study in which effects of exchanging SAFA by mono unsaturated fatty acids or carbohydrates with or without supplementation of omega-3 fatty acids were studied during 12 weeks. In the third study presented (the SATgene study) a low fat and 2 high fat diets (with or without additional omega-3 fatty acids) were compared . From the three studies presented professor Lovegrove concluded that exchanging SAFA for carbohydrates did not improve metabolic dyslipidaemia and had no effect on insulin sensitivity, irrespective of glycemic index. She also mentioned that there is limited evidence that this exchange may improve vascular functions, but results need to be investigated further.
Then associate professor Marianne Jakobsen (Aarhus University, Denmark) presented her results from observational cohort studies in which the exchange of nutrients was studied. Her meta-analysis of 11 cohort studies revealed that the risk of coronary heart diseases was reduced if SAFA were replaced by polyunsaturated fatty acids, but was increased if SAFA were replaced by carbohydrates. The latter result was confirmed in a follow-up cohort study, where the risk on myocardial infarction was increased if SAFA were replaced by carbohydrates. Nevertheless, this study also revealed that the type of carbohydrates determined the risk: carbohydrates with a high glycemic index increased the risk but not carbohydrates with medium or low glycemic indices. Dr Jakobsen concluded that more research on macronutrients substitution will contribute to define overall dietary patterns.
Professor Bruce German (University California, USA) gave an overview of the importance of SAFA in the diet based upon the conservation of the milk protein genes throughout evolution. He explained that dietary SAFA raise blood cholesterol since they activate a hepatic gene called PGC-1ß which further stimulates the production of endogenous fatty acids and the formation of VLDL. Professor German described it as an effective mechanism to provide energy in situations like exercise, lactation, during infancy and acute phase immune response; consequently SAFA are not only used for energy but also function as signalling molecules. He concluded that there is no evidence supporting the assumption that SAFA at any level are deleterious. Diets high in fat and SAFA are associated with increased risk in certain groups, but not on population level. He also stated that there is a need to shift from population based recommendations to more personalized nutrition. This approach should also take into account genetic differences,, life stage and life style which ultimately lead to variations in responses to the diet including SAFA.
That dietary recommendations should not focus on nutrients like SAFA was highlighted by associate professor Dariush Mozaffarian (Harvard University, USA). He began his presentation by giving an overview of the weakness of the evidence for recommending less total fat in the 1960s-1970s.At that time there were no data available from well controlled studies. Recommendation on total fat was then expanded to less SAFA intake. Dr Mozaffarian explained that nutrition science evolved from prevention of deficiency by one nutrient to prevention of chronic diseases, where many factors are involved and for which correlations among nutrients must be taken into account. Evidence based on well-controlled studies (observational studies as well as intervention trials) today shows that replacing SAFA by polyunsaturated fatty acids is beneficial for the risk of coronary heart diseases. The replacement of SAFA by carbohydrates has no beneficial effect on this risk. Looking at the current composition of the typical American and Western diet, with lots of carbohydrates it might be a better advice to increase the intake of polyunsaturated fatty acids by exchanging the overload of carbohydrates with a high glycemic index and promoting the intake of fruits, vegetables, vegetable liquid oils and nuts. Dr Mozaffarian finally advised to set recommendations on foods rather than on nutrients as currently done.
The next speaker was Dr Pramod Khosla who presented the outcome of the Symposium “Health Effects of Saturated Fatty Acids” held at Wayne State University, USA, Oct 14, 2010. The Symposium covered three essential areas – US Dietary Guidelines in relation to fat, role of fat in low-carbohydrate diets and saturated fat/fatty acid effects on health in light of current knowledge. The outcome of that session was that recommendations for SAFA so far have led to unintended consequences and therefore SAFA may not warrant the focus that it has received for a long time. Moreover, decreasing the intake of SAFA from the diet is only beneficial in terms of health outcomes if the replacement nutrient is chosen wisely.
Associate professor Ingeborg Brouwer (Free University of Amsterdam, The Netherlands) discussed the health effects of SAFA and trans fatty acids. She also agreed with the findings of previous speakers that SAFA replacement by unsaturated fatty acids is beneficial for the risk of heart diseases and that a distinction between individual SAFA on health effects can not be made yet. Dr Brouwer then stressed that health effects of all trans fatty acids are comparable and unbeneficial since they raise LDL-cholesterol, decrease HDL-cholesterol and therefore increase the ratio between total and HDL-cholesterol. This is irrespective of the source (ruminant or industrial) and the number of double bounds in the trans configuration.
The last speaker of the SAFA session was Dr Peter Zock (Unilever R&D, The Netherlands) who reviewed the health effects of structured fats (interesterified). He started with emphasizing that interesterification enables production of foods virtually free from TFA and lower in SAFA while keeping the desired functional properties, and that interesterification is not necessarily a synthetic process since it occurs in the enterocyte (a cell of the intestinal wall) after fat absorption (re-arrangement of free fatty acids at the glycerol backbone). In his presentation Dr Zock reviewed fifteen human intervention studies, described in literature, on the possible health effects of the position of SAFA in dietary TAG,. The conclusion was that available human data do not support adverse acute or chronic health effects of interesterification or of fats rich in SAFA at the sn-2 position.
During the panel discussion the topic of the SAFA session was discussed: is the recommendation for 10 energy percent of SAFA the right recommendation and what would be the right replacement? The panel agreed that replacing SAFA by poly unsaturated fatty acids is beneficial for the risk of coronary heart diseases based on the scientific evidence from both observational and intervention studies. However, the health impact of SAFA can vary between humans and whether it is still needed to focus on a reduction of SAFA was discussed. Historically, the focus has been on the relation between cholesterol and heart diseases, but more factors and markers are involved and they need to be investigated further. Reducing the dietary SAFA intake in the past decades has been beneficial for example in Finland said Dr Brouwer. However, Dr Jakobsen and Dr Mozaffarian emphasized that the focus about recommendations should go from macronutrients to foods, since there is more than the single macronutrient. Mozaffarian mentioned that in his opinion there are only few dietary actions that really matter: they include the reduction of trans fatty acids and salt, the increase of omega-3 fatty acids and the increase in the consumption of fruits and vegetables. Furthermore, attention should be given to the carbohydrates quality and in the reduction of processed meats, particularly rich in salt. There need to be a priority setting within these recommendations, and in Dr Mozaffarian’s opinion the main focus should be on promoting healthy foods in general and to stimulate a well-balanced dietary pattern. Dr Zock stated that SAFA still deserves more research before it can be said that it is not important to further reduce it. Further, it was suggested that there may be a threshold in the intake of SAFA dependent on the polyunsaturated intake: if dietary intake of polyunsaturated fatty acids is at least 5-6 energy percent then the intake of SAFA might well not matter anymore. Dr Mensink responded that he did not find any interaction between polyunsaturated and SAFA intake in his data. Finally the issue of an upper limit for the intake of poly unsaturated fatty acids was raised. However, like the correlation between SAFA and polyunsaturated fatty acid intake, also the limit for polyunsaturated fatty acids was left without a clear consensus since this is still under debate.
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