I was presenting a lecture a short while back that included fatty acids and inflammation and how they can impact things like osteoarthritis. I explained the structure of omega-3 (linolenic) and omega-6 (linoleic) fatty acids, and that omega-3 fatty acids were anti-inflammatory,and omega-6 was pro-inflammatory. Someone posed a great question; “why not stop feeding the omega-6 fatty acid”.
While that is probably doable, there is a major reason both of these fatty acids are required. These two classes of fatty acids are known as essential fatty acids and as such they must be in the diet. Animals can make the other fatty acids from precursors, but these two are different. Both are polyunsaturated fatty acids, meaning they have multiple double bonds located in specific places in the molecules that affect their functions in the body. The primary difference is the location of the first double bond, shown below in a red circle.
In the body, linoleic (omega-6) is metabolized to form a 20 carbon molecule with four double bonds called arachidonic acid. Arachidonic acid is the precursor for all the prostaglandins in the body. Prostaglandins have several functions in the body, some of which are 1) an activate inflammatory response resulting in fever and pain; 2) affect blood vessel constriction and blood clotting; 3) reproduction and 4) impact leukotriene production which impacts bronchi in the pulmonary system. Specific enzymes can convert arachidonic acid to specific eicosanoids that are pro-inflammatory, increase blood clotting and increase vasoconstriction. Excess omega-6 fatty acid can lead to an acute pro-inflammatory response,it can also cause prolonged stimulation of inflammation or a diminished response post-injury. This can lead to chronic inflammation and long term health issues.
Linolenic in the dietis metabolized to longer chain fatty acids, eicosapentaenoic (EPA) and docosahexaenoic acid(DHA). These two fatty acids can also be obtained in the diet from marine sourced and some micro-algae sourced feedstuffs. EPA and DHA both are metabolized to specific eicosanoids that help resolve inflammation.
The following diagram is intended to help see how each fatty acid impacts the inflammatory response.Somedietary sources are also given.
The daily requirement for either linoleic or linolenic fatty acidis not clearly defined for the horse, we do know the ratio may be more important than the exact intake. It is the competition for the desaturase and elongation enzymes that make one fatty acid pro inflammatory and the other anti-inflammatory.In keepingwith the theme of not knowing exact requirements, no one can define the perfect ratio of omega-6 to omega-3 fatty acids. It appears to be between 2:1 and 5:1 in the total diet. Corn, safflower, rice bran and sunflower oils all contain extremely high percentages of omega-6 fatty acid relative to omega-3. Good sources of omega-3 fatty acid(linolenic)include green plants, canola oil and flaxseed oil.Soybean oil is acceptable since it has about a 5:1 omega 6:omega 3. Dietary sources of EPA and DHA are primarily fish and fish oils. Neither of these two are very palatable to horses. In the last several years there has been an interest in oils derived from certain species of algae. These oils can contain as much as 27% of the total fat content being DHA. Unlike palatability of fish oils, horses do not have negative intake issues with micro-algae oil.
Just leaving omega-6 fatty acid out of the diet may seem like a good approach to limit the inflammation that is caused by this fatty acid, further investigation demonstrates the answer is not quite so simple.Providing too much omega-6 especially in relation to the amount of omega-3 fatty acid is a much larger problem in today’s feeding programs. While there are numerous sources of omega-6 used in the horse’s diet, choices for including omega-3 fatty acids are limited, quite expensive and often found in short supply in feed products. Should we feed the oil to meet calorie needs and by controlling total intake be in a less inflammatory position?