Food Insight Interviews Dr. Bill Harris on Omega-3 and Omega-6 Fatty Acids

Dr. William Harris holds a PhD in Nutritional Biochemistry from the University of Minnesota. His research has focused on human lipid and lipoprotein metabolism, especially as it is affected by omega-3 fatty acids. He has been the principal investigator on five omega-3 related NIH grants, and is currently evaluating the "omega-3 index" as a new risk factor for cardiovascular neuropsychiatric diseases. In 2011 Dr. Harris became a Senior Scientist at Health Diagnostic Laboratory, Inc. (Richmond, VA). He retains an academic appointment as Research Professor of Medicine at the Sanford School of Medicine, University of South Dakota in Sioux Falls.

FOOD INSIGHT:  The 2010 Dietary Guidelines were released earlier this year.  What do they recommend regarding fat consumption?  Has it changed from 2005? If so, how?

DR. HARRIS:  The 2010 Dietary Guidelines for Americans still recommend that 20-35% of our calories come from fat, just as they did in 2005.  An emphasis remains on reducing intake of saturated fat and trans fat by replacing them in the diet with poly- and monounsaturated fats.  What’s different in 2010 is the new target for consumption of ≥250 mg per day for long-chain omega-3 fatty acids—Eicosapentaenoic acid (EPA) and Docosahexaenoic acid (DHA).

FOOD INSIGHTConsumers hear a lot about the benefits of omega-3 fatty acids.  Why are they so highly recommended to consume?

DR. HARRIS:  Dietary fats are categorized by the number of double bonds they carry. If they have more than 1 double bond they are called “polyunsaturated fatty acids (PUFAs).” The omega-3 fatty acids are PUFAs — the healthful fats recommended to replace saturated and trans fats in our diet.  Because of their anti-inflammatory and anti-coagulant properties, omega-3s have been shown to protect against cardiovascular disease, fatal heart attacks, arrhythmia, and arthritis.  There are different types of omega-3’s however.  Alpha-linolenic acid (ALA) is found in plant sources and Eicosapentaenoic acid (EPA) and Docosahexaenoic acid (DHA) are found in marine sources.  EPA and DHA have shown the most cardio-protective effects.

Omega-3 consumption is also encouraged because of their deficiency in American diets.  American intake of EPA and DHA is too low—current daily intake is around 150 mg per person per day, and although the new Dietary Guidelines stipulate at least 250 mg/day, many omega-3 specialists think that the target should be higher, approximately 500 mg/day.

Foods with the highest sources of omega-3 come from cold water oceanic environments.  Oily fish such as albacore tuna, anchovies, herring, mackerel, salmon, and sardines are all good sources.  Fish with low omega-3 content are “dry” fish like bass, catfish, cod, and tilapia.  Most shellfish contain very little omega 3’s with the exception of oysters, which surprisingly have lots of omega-3’s.

FOOD INSIGHT:  Consumers hear less about omega-6 than they do about omega-3.  What should the average consumer know about omega-6 fatty acids?

DR. HARRIS:  Like omega-3’s, omega-6’s are also classified as polyunsaturated fatty acids (PUFA).  Also like omega-3’s, not all omega-6’s are the same.  The most prevalent omega-6 fatty acid in our diet is linoleic acid.  Before being characterized as a fatty acid, linoleic acid was actually thought to be a vitamin—it used to be called Vitamin F for “fat.”  Omega-6 fatty acids are most typically found in salad dressings and vegetable oils such as corn, peanut, soybean, and sunflower oils with small amounts in canola and olive oil.  The linoleic acid content of these oils will vary.

Some people think omega-6 fatty acids should be avoided because they are purported to promote an inflammatory response in the body, which actually is not true.  Some metabolites of omega-6’s are inflammatory and some are anti-inflammatory.  The problem, however, is not the prevalence of omega-6 in the American diet; it’s the lack of omega-3’s, which are less inflammatory.  Omega-6 fatty acids are highly regulated in the body.  When omega-3 fatty acids aren’t present in sufficient quantities, the body uses arachidonic acid (which is an omega-6 fatty acid) as a substrate for making prostaglandins, which are responsible for the inflammatory response.

FOOD INSIGHTIn the nutrition world, we hear about omega-6:3 ratios in the food supply.  Can you clarify for health professionals and consumers what the ratio means and if it’s something they should be concerned with?

DR. HARRIS:  The omega-6:3 ratio refers to the comparative amounts of each of these specific fatty acid groups in your overall diet.  However, there are fundamental problems with using a ratio in dietary recommendations.

  • All omega-3s and all 6’s are not created equal, so how useful is a ratio in dietary guidance if it doesn’t define which sources of omega fatty acids to include?
  • Typically a ratio compares one bad thing to one good thing.  Both omega-3 and omega-6 fatty acids have been scientifically proven to benefit cardiovascular health. So both parts of the omega-6:3 ratio are good, which violates the reasoning behind creating such a ratio in the first place.
  • You can achieve a target ratio with a variety of intakes—both small and large amounts.  Therefore, amounts become irrelevant in ratios, but intake amounts of omega fatty acids are the most important factor.

FOOD INSIGHT:  Consumers hear even less about omega-9 fatty acids.  Are these fats healthful to consume?

DR. HARRIS:  Unlike omega-3 and omega-6 fatty acids which are polyunsaturated fats, omega-9’s are monounsaturated fatty acids (MUFA).  Omega-9’s (oleic acid) are the most common fat on earth—you can find it in canola and olive oils, avocado, and meats as well. They are generally thought to be healthful, but they do not provide the cardio-protective benefits of omega-3s.

FOOD INSIGHT:  Where do you see the future of dietary fats research and recommendations going?

DR. HARRIS:  The area I’m the most familiar with is omega-3 fatty acids.  In the future, it will be important to define optimal intakes of specific omega-3’s (EPA and/or DHA) for prevention of specific disease states.  I’ve explored the utility of measuring blood omega-3 index as a risk factor for chronic disease.  Currently, you can measure things like blood pressure and cholesterol to determine risk, why not omega-3?  It’s possible that a low “omega-3 index,” (red blood cell EPA+DHA) is an independent risk factor, like cholesterol, and could turn out to be an important predictor for heart disease.