Annchen Weidemann | Dietician Western Cape
Omega Fatty Acids: Time To Get The Messages Right
Annchen Weidemann, Dietician, Western Cape
December 21 2017
In a very recent editorial review in Current Opinion in Clinical Nutrition and Metabolic Care, the importance of understanding the difference and interaction between the essential fats is highlighted by Dr. Philip Calder. The exact nature of the effects and complexity of essential fats have been poorly communicated, among the various stakeholders, but especially to the consumer. “The omegas”, or “omega fats” have been used as generic references, implying that there is only one type of this fatty aid, or that different types of this fatty acid have the same nutritional properties and health benefits. This is clearly wrong. Polyunsaturated fatty acids (PUFAS) are categorized by the presence of two or more double bonds, and also where the first double bond is located, in relation to the first carbon in the chain. Omega-3 fatty acids have their first double bond at the third carbon, while omega-6 fatty acids have their first double bond at the sixth carbon. The simplest omega-3 and -6 fatty acids are the 18 carbon linoleic and α-linolenic family found in most plant oils.
Humans are unable to insert double bonds into fatty acid chains, meaning they have to be supplemented by our diet. These 18 carbon fatty acids are now desaturated and elongated to form 20 and 22 carbon fatty acids (fig.1). Only in this form can they be incorporated into cell membranes and metabolised to bioactive eicosanoid mediators. Omega-6-fats yield Arachidonic Acid (AA) which is the precursor to the aggressively inflammatory mediators, while omega-3 fats yield EPA and DHA, which are precursors to much less inflammatory or even anti-inflammatory mediators. The problem here is that from the plant origin, the conversion of omega-3 to EPA and DHA is much less efficient than the conversion of n-6 to AA. Only if EPA and DHA are supplied in our diet as such (from fish and fish oil) can the powerful inflammatory response from omega-6 be attenuated.
Because the simple omega-6 and omega-3 fats share and compete for the same enzymes in their elongation and desaturation, omega-6 mostly wins and forms AA, because its quantity in plant oils (and the western diet in general) is up to 20 times more than omega-3. The ideal ratio of n-6 : n-3 is probably no more than 2:1, for optimal conversion of α-linolenic acid to EPA and DHA. It is evident that the effects of α-linolenic acid and “fish omega-3 fatty acids” are not the same, and head to head comparisons or the two have shown this to be the case. The comparisons have shown that α-linolenic acid does not exert the same effects as a combination of EPA and DHA and that, where there are similar effects, α-linolenic acid is 10-fold less potent on a gram-to-gram basis. There is hence no basis for making generic “omega-3” claims.
More education needs to be done to the public and other regulating bodies that there are two “forms” of omega-3 fats – a “plant form” and a “fish form”. In addition, while it may be important to increase the intake of both, it is the fish form that is clearly the most beneficial to health. On this basis, and quite rightly, regulatory authorities attempt to convince consumers to eat more fish, but sadly many people do not like to eat fish or have any access to it, so they are missing out on the health benefits of fish omega-3 fatty acids.
One alternative is to use fish oil supplements which allow for a regular and significant intake of EPA and DHA, and particularly now that “high strength” capsules are becoming available. One of the issues of supplementation might be lack of sustainability of supply. There has therefore been an interest in other sources of EPA and DHA, and algal sources of DHA are already available and used in the infant formula industry. Another strategy has been EPA and DHA enrichment of foods not normally rich with these fatty acids.
Two routes have developed: the addition of fish oil to products such as spreads, yoghurts and milk, and secondly, the feeding of farm animals with omega-3 fatty acids, resulting in enrichment of meat, milk and eggs with EPA and DHA. The level of enrichment that can be achieved is severely limited by metabolic processes in the animals and food technology, processing and storage conditions. The level of enrichment which can currently be achieved by a combination of several enriched products is limited to a few hundred milligrams of EPA and DHA. The author warns the food industry not to use foods high in saturated or otherwise inflammatory fat and sugar as a vehicle to provide a very small amount of EPA and DHA per portion. In short, healthy ingredients such as EPA and DHA should not be incorporated into less healthy foods. The taking of n-6 supplements is without any substantiation, considering the high intake of this fatty acid through typical western eating already. n-9 (oleic acid, found in olive oil) is a mono-unsaturated fat, and non-essential to the human body. Omega-12 and 15 are a joke (contact me for more information). Please help your patients not to spend their money on these supplements.
Dr. Calder concludes: “…to maximize the effectiveness of omega-3 fatty acids in optimizing human health and wellbeing,…and to educate the public in such a way that they can make informed choices about healthy eating, it is vitally important that the messages about these fatty acids be simple, clear and correct.”
Omega fatty acids
n-3 and n-6 fatty acid metabolism
Parenteral lipid emulsions: Lipids in the form of olive oil and milk, for example, have been administered intravenously to humans for therapeutic purposes since the 17th century. Numerous adverse events resulting from lipid use led to the notion that the administration of fat by this route invariably causes severe complications, including fat embolism. The demonstration of a strong link between malnutrition and post-operative mortality in 1930 by Studley, was a strong impetus for further exploration of intravenous fat solutions which would provide a more balanced supply of energy, along with glucose. After much trial and error, Schuberth and Wretlind succeeded in developing a non-toxic lipid emulsion from soybean oil, which was introduced into parenteral nutrition formulas in the 1960’s. The linolenic acid (n-6 fatty acid) content of soybean oil comprises 54% of the fatty acids present, while only 8% of the total fatty acids are in the “plant form” of omega-3, α-linolenic acid.
In 1998 Heylandt conducted a meta-analysis (the largest of its kind) of TPN and found that the inclusion of lipids might be detrimental in very ill patients. The only benefit was seen in severely malnourished patients. Soybean oil-based TPN-solutions were used in most of the studies included in the meta-analysis. In a satellite symposium on “Fish oils: a parenteral perspective”, Dr. Philip Calder explains that an excessive supply of n-6 PUFA in TPN could act to promote, or at least exacerbate states of inflammation and immunosuppression. This situation could occur particularly in very ill or injured patients, for whom TPN may be indicated, especially if the GIT is not functional. At the ESPEN conference of 2006 held in Istanbul, Turkey, Prof. Calder introduced a symposium held on the benefits of olive oil. These talks shed much more light on the detriments of an excessive supply of soya oil in TPN, not only because of the inflammatory effects of omega-6, but also because of “double-bond overload”, providing 50% of the total fat as polyunsaturated. The double bonds in polyunsaturated fats are unstable and cause an increased rate of lipid peroxidation, creating free radicals that in turn place the patient in a state of high oxidative stress.
Our intake of polyunsaturated fat is generally not more than 5 – 7 % of our total fat intake, and it is internationally recommended that our PUFA intake is 10% of total fat. Prof. Calder says “..the use of lipid emulsions based entirely on soybean oil in parenteral nutrition may not be optimal or may even be harmful. The concern about potential harm, the view of sepsis as a hyper-inflammatory state followed by an immunosuppressed state and the idea that n-6 PUFA might be “pro-inflammatory and immunosuppressive”, have led to the development of alternative lipid emulsions for parenteral applications.”
During an accredited CNE held in Cape Town, where Prof. Robert Martindale spoke on immune-nutrition, he set the internationally accepted guideline: if you are faced with a choice between soyabean oil TPN or non-fat TPN, give non-fat TPN for the first 7 days in ICU. What can we do? Olive oil-based TPN is widely available. It is not the complete solution, but it alleviates the situation:
➢ only 9% of the total fat is n-6
➢ 1% of the total fat is n-3 but it is “plant omega-3”, which probably negates its presence
➢ 75% of the total fat is mono-unsaturated fat, which provides a much relieved “double-bond overload”, and cause less oxidative stress.
What is the answer? The addition of parenteral fish oil. It has been widely studied with exciting and promising results. It is not available in SA yet, the companies claiming problems with registration. It will be in the form of SMOF (soya oil, MCT, olive oil and fish oil) which will be the general fat emulsion in your TPN bag, or a vial of additive fish oil, which you are able to add to IV fluids (I have asked but could not ascertain whether it will be water soluble or not). What about the fat content of enteral nutrition? Obviously, the same applies. Unfortunately enteral feeds are still largely based on n-6 rich plant oils such as sunflower, soyabean, safflower and corn oil, an issue which should be addressed with the same vigour as the fat content of TPN.
Good studies have shown the benefits of additional EPA in cancer cachexia, showing weight stabilization and significant increases in lean body mass, even in advanced pancreatic cancer (Barber et al., 1999). The ESPEN guidelines to cancer nutrition also highlight the potential benefits of including additional EPA and DHA. There are excellent review articles available that elude to the benefits of using added EPA and DHA – I can provide you with copies if you are interested.
I will dedicate a newsletter in future to the issue of omega-3 fats in cancer nutrition. Interestingly, newly launched feeds with the cancer patient as the target population, had sunflower (71% n-6) and safflower (76% n-6) oils as the fat component, with no additional fish oil.
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