International Omega-3 Learning and Education Consortium for Health and Medicine

The health benefits of omega-3 fatty acids are reported more and more frequently and include benefits from heart health to improved cognition and inflammation, with emerging evidence for other benefits as well; but do you know what omega-3 fatty acids are?

First and foremost, omega-3 fatty acids must be consumed in our daily diets; they are essential because the body cannot synthesize them from other types of fat in the diet. The essentiality is based on the chemical structure of these fatty acids and where the chemical bonds are located along the fatty acid structure. It's the location and amount of double bonds and length of the fatty acid chain in its chemical structure that determines the biological importance of the essential fatty acid with regard to nutrition and health. In contrast, saturated fatty acids, found in lard and butter, have no double bonds and monounsaturated fatty acids, found in olive oils, almonds, and avocados, have one double bond. The body can synthesize these types of fatty acids and they are not essential.

The families of essential omega-3 and omega-6 fatty acids are polyunsaturated fatty acids. Polyunsaturated fatty acids have two or more double bonds in the fatty acid molecule. Omega-3 fatty acids are found in foods such as walnuts, canola oil, marine cold water fish and fish oils (for more examples please see Food products). The omega-3 fatty acids have at least three double bonds starting from the 3^rd carbon from the methyl end of the fatty acid molecule as shown in the chemical structure of eicosapentaenoic acid or EPA. Omega-6 fatty acids are found in a number of vegetable oils including corn oil, soybean oil, safflower oil and sunflower oil and when these oils are processed and partially hydrogenated the polyunsaturated fatty acids can become trans fatty acids. Omega-6 fatty acids are also found in eggs and meats, margarine and numerous baked or processed foods. The omega-6 fatty acids have their first double bond at the 6^th carbon from the methyl end of the molecule as shown in the chemical structure of arachidonic acid or AA.

For those of you who are visual learners, below are the structures of EPA and AA; both fatty acids have 20 carbons. Each point on the line structure shown below represents a carbon atom, so go ahead and count them! The ends of these molecules have names to describe the fatty acid structure. The left end is the COOH group which is called the carboxyl end and the right end is the methyl end. The number of carbons (points on the line structure shown below) before the first double bond counting from the methyl end differentiates the omega-3 fatty acids from the omega-6 fatty acids. As illustrated below, the omega-3 fatty acid EPA has its first double bond (illustrated with two horizontal lines) located at the 3^rd carbon counting from the methyl end of the structure. Hence, the location of the first double bond counting from the methyl end makes EPA an omega-3 fatty acid because the first double bond in its structure starting from the methyl end is in the 3^rd position. Also shown below is the omega-6 fatty acid AA. For AA the first double bond in the structure counting from the methyl end is at the 6^th carbon. Therefore, AA is called an omega-6 fatty acid because the first double bond counting from the methyl end is in the 6^th position.

While omega-6 fatty acids are essential, the Western diet contains an excessive amount of these fatty acids because of the fats and oils consumed compared to the amount of omega-3 fatty acids. One way to compare this relationship of omega-6 and omega-3 fatty acids in the diet is the ratio between the two families of fatty acids. The ratio of omega-6 fatty acids to omega-3 fatty acids should be low (i.e. 3:1 or 5:1); however, American intake ratios range from 10:1 to 17:1 for the omega-6 fatty acids to omega-3 fatty acids ¹. Americans should consume more omega-3 fatty acids for proper nutrition and health.

What makes the omega-3 (and omega-6) fatty acids even more challenging for the consumer is that within the omega-3 family, there are different types of food sources for these fatty acids. Alpha-linolenic acid (ALA) is the essential omega-3 fatty acid and it is present in walnuts, flax oil and canola oil. ALA can (to a very limited extent) be converted to the more active forms of omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are associated with most of the omega-3 health benefits. However, the conversion of ALA to EPA and DHA is poor; so to get EPA and DHA, it is best to consume sources containing these fatty acids such as marine cold water fish (i.e. salmon, mackerel, or tuna [fresh or canned in water]), and foods fortified with EPA or DHA (please refer to Food products).

Recommendations for ALA intakes in the United States were made the last time that the macronutrient (fat, protein, carbohydrates) dietary reference intakes (DRI) were revised (2005) by the Institute of Medicine, and other countries have similar recommendations (please see Recommendations for omega-3 fatty acids). The DRIs recommend an adequate intake (AI) for ALA at 1.6 g/day and 1.1 g/day for men and women, respectively. The acceptable macronutrient distribution range (AMDR) was 0.6% to 1.2% of energy intake and this should be from omega-3 fatty acids with 10% of this requirement from EPA and DHA. The percentage of energy intake refers to the amount of calories (energy) in the entire daily diet, or the total calories consumed in one day. Recently a paper was published in the Journal of Nutrition to support a requirement for EPA and DHA ², so we await a scientific consensus for a recommendation.

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