Why the omega-3s in walnuts are not the same as the ones in fish and algae

[Global] There seem to be an awful lot of articles suggesting that people have a handful of walnuts or seeds to get their omega-3 fatty acids. While this isn’t wholly bad advice, it’s not exactly the most accurate. The problem is it assumes all omega-3s are interchangeable, when in fact they’re not. There are actually several different iterations of the fats, and unfortunately the ones that come from plants are not as healthy as the ones that come from fatty fish (and happily for vegetarians, algae).

Here’s a brief rundown: The variety of omega-3s in plants is α‐linolenic acid (ALA). The omega-3s in fish are eicosapentaenoic acid (EPA) and docosapentaenoic acid (DHA). Humans aren’t able to make EPA or DHA from scratch; we need either to eat them or to form them from shorter fatty acids (like ALA). The body is able to convert ALA into EPA and DHA through a chain of chemical reactions that generally take place in the liver. In this sequence of events, DHA is the final product, arriving a couple of steps after EPA. (For a detailed breakdown of all the reactions needed to take ALA to DHA, see this.)

The problem is that the conversion isn’t very efficient, with only a small percentage of ALA making it all the way to DHA. This is partly due to competition from omega-6 fatty acids, which people tend to eat in higher quantities than omega-3s in general.

“The human body can convert the plant omega-3s into the fish omega-3s but in many people this process does not seem to work very well,” says Philip C. Calder, a professor of Nutritional Immunology at the University of Southampton who studies omega fats. ”One reason for that might be the high amount of omega-6s that people eat – these stop the body’s conversion of plant omega-3s.”

So people who rely on the omega-3s from plants may still be low on DHA and EPA, since the conversion isn’t so efficient. In other words, eating walnuts to get your omega-3s may not be enough. “It is very important for consumers to be aware that some omega-3s come from plants and some come from fish,” says Calder. “These omega-3s are not the same thing.”

The larger issue—and the reason any of this matters at all—is that the different omega-3s have different effects on our health. The long-chain fatty acids, EPA and DHA, are well known to reduce inflammation in the body, and are particularly good for the cardiovascular system, reducing heart disease risk, and for the brain, reducing the risk of dementia. They are also important to the developing brain—pregnant women should take special care to take in enough. The bulk of ALA, which isn’t converted to EPA and DHA, still plays important roles in the body, from the structure of cell membranes to use as energy or energy storage. And omega-6s, though essential in low levels, are linked to inflammation at higher levels. Most people eat many more omega-6s, which are found in a number of foods including poultry, eggs, grains, and nuts, than omega-3s of any type.

So keep in mind the difference in the omega fats, and most importantly, the fact that while DHA, EPA, and ALA all fall under the omega-3 umbrella, they’re not interchangeable. Lumping all omega-3s together may not be wise. Lumping omega-3s and omega-6s together is probably even less wise.

“There is a role in human health for both the plant and fish omega-3s,” says Calder, “but the fish omega-3s are more active in the body. Ideally people will get their omega-3s from foods like fish.” If you don’t eat much fish, you may want to supplement with fish oil supplements. And for those who don’t eat any fish, algae oil supplements will do just fine, since algae contains DHA. In any case, remember that omega-3s from the land are ok, but the ones from the sea are much better.

 

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