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Omega 3 & Fatty Acids

  1. I've always been overweight so I try to eat as little fat as possible. Is there is a way to tell if my diet is actually low in fat and if it supplies me with the fatty acids I need? Answer
  2. Your answer included the statement that the human body can make linolenic and arachidonic from linoleic. This is only partially true. Answer
  3. You mention that linoleic acid is the only truly essential fatty acid. Linolenic is an omega 3 fatty acid. Fish is the only abundant source. Answer

I've always been overweight (10-15 pounds), so I try to eat as little fat as possible. However, I know that I need to eat some fat in order to get the essential fatty acids. I was just wondering if there was any way to tell if my diet is actually low in fat and if it supplies me with the fatty acids that I need?

You can't live without eating some fat and the very minimum amount you need is 1 teasoon of polyunsaturated oil per day to prevent fatty acid deficiency. However maintaining this very low level is practically impossible unless you only eat fruit which would be unhealthy because it would be lacking in many vitamins and minerals as well as protein.

Without writing down everything you eat and performing a nutrition analysis, you would only be making a rough guess about how much fat you eat. Sure, butter, margarine, oil, mayonnaise, salad dressing and fat in meat or milk are more obvious, but did you know that tofu, avocados and coconut contain fat? Fish like wild salmon (not farmed), albacore tuna, herring and sardines are high in omega 3 fats.

I would suggest you write down everything you eat and send your food records to a dietitian who can analyze what you eat. Their reports will show the percent of the different types of fat (saturated fat, monounsaturated and polyunsaturated) as well as the amounts of the various fatty acids.

Most importantly, a dietitian's report could include the ratio of omega 6 to omega 3 fatty acids. Research has indicated that omega 6 fatty acids (mostly polyunsaturated vegetable oils) may only be helpful in keeping cholesterol levels in the blood low. Whereas, omega 3 fatty acids (fish oils) may decrease risk of abnormal heartbeat, triglyceride levels, cholesterol deposits on artery walls and lower blood pressure. Omega 3 fats also reduce platelets from clumping, making them less sticky and less likely to form a blood clot. In fact, the ratio (1:1) between these two types of polyunsaturated fatty acids appears to have as much importance as the ratio of saturated to unsaturated fats in the foods a person eats. This is still being studied and recommendations for Americans to change the type of fats in their food choices has not yet been made.

Your other alternative is to purchase some nutrition analysis software and do the work yourself. The problem is that very few software packages include a database of fatty acid content in foods and these packages are usually written for nutrition professionals, which are expensive.

The purpose behind your service is great. Accurate nutritional information to the consumer is a must. I stumbled on your information concerning fatty acids and found some errors that I would like to clarify just for your information. Your answer included the statement that "the human body can make linolenic and arachidonic from linoleic. This is only partially true as only arachidonic can be synthesized from linoleic. Linoleic is also termed an omega-6 fatty acid and linolenic is omega-3 fatty acids these two structures can not be interconverted. Also the amount of linoleic derived from most fish is very small. Fish is very rich in 20:5 and 22:6, which they attain from marine microalgae. Fish is really the only abundant source of these two fatty acids which makes it very important in our diet. Keep up the good work.

Mary VanElswyk, PhD RD Texas A&M University

Thanks for the additional information. I have clarified other questions on linoleic acid.

The whole subject of good and bad fat is very confusing for the consumer. Most persons want to know how to eat healthy and sometimes making healthy food choices is perplexing to the public due to all the science. The point being people should choose healthy fats like olive, peanut, Canola, soy, corn, sunflower, safflower, cottonseed oils. Foods high in omega 3 fats like salmon, tuna, herring, sardines, anchovies,walnuts and Canola oil. Omega 6 fats (linoleic) are found in polyunsaturated oils like corn, soy, sunflower. Actually many oils are a combination of fatty acids rather than just exclusively omega 3 or just omega 6.

On the nature of EFA's, you mention that linoleic acid is the only truly essential fatty acid (EFA). While this may be so, it glosses over the effects of an under supply of linolenic acid in the diet, because when eicosadienoic acid is synthesized and substituted for (gamma) linolenic acid in the w-3 eicosanoid pathways, the rates of peroxidation, cyclooxygenase activity, desaturase activity and reaction products are altered. Thus it seems very helpful to include both EFA's in the diet for proper functioning of the arachidonate / eicosanoid synthesis pathways in humans. (Not to mention the many journal articles on the triglyceride and LDL lowering effects of fish oils over the past several years) It's sort of like the question of "folic acid or cobalamin"? To me, I would ask "why not both'?

The human body is supposed to be able to make some linolenic and most arachidonic fatty acids from linoleic acid. Previously, all three were considered essential fatty acids (EFA) before the metabolism of these fatty acids was understood.

Linoleic acid is found in butter, cocoa butter and coconut oil as well oils from corn, cottonseed, olive, palm, palm kernel, peanut, rapeseed (Canola), safflower, sesame, soybean and sunflower. Butter, coconut, palm and palm kernel are saturated fats and the others are monounsaturated (olive and peanut) or polyunsaturated (corn, cottonseed, rapeseed, safflower, soybean and sunflower. Sesame oil contains about equal amounts of mono and polyunsaturated fats.

Linolenic and arachidonic fatty acids are also found in these same food sources of fat.

The essential fatty acids found in fish oils are linolenic (18:3), timnodonic (20:5) and docosahexaenoic (22:6). Including two or three servings of broiled or baked fish per week in the diet has been recommended mostly because fish is generally lower in fat than red meats. Some fresh and salt-water fish are high in fat (trout and mackerel).

As to your comment about folic acid (important vitamin in the synthesis of new cells, especially during pregnancy to prevent neural tube defects) and cobalamin (vitamin B-12 which is important in the manufacture of red blood cells), their functions are equally important for which there are Recommended Dietary Allowances.

PS My "Ask the Dietitian" format is intended for the general public as a source of nutritional information, not a forum for scientists to debate in technical terms what only nutrition scientists understand. Most people want to know what to buy at the grocery store and how to eat healthy foods. Thank you for your comments.

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