Purslane as a source of omega-3: a reality check

Saturday, October 17, 2009 13:37
Comments Off on Purslane as a source of omega-3: a reality check

Q. Why does Nutrition Data show purslane as having no omega-3 fatty acids,
when it is very high in omega 3?

A.  First a quick clarification: When a value is known to be zero, you'll see a "0".  The tilde symbol "~" indicates an unknown value. So, our listing doesn't indicate that purslane has no omega-3 fatty acids, it indicates that the amount of omega-3 fats are unknown.  (For more on this unfamiliar vegetable, see this post: "On today's menu: Weeds.")

But this still raises an interesting question:

Why wasn't omega-3 content in purslane measured?

The USDA's nutrient data lab doesn't test every food for every nutrient. It would be a waste of time and money, for example, to analyze carrots for cholesterol because plants don't contain cholesterol. But when a food is known or thought to be high in a particular nutrient, that nutrient usually is included in the analysis.

Purslane has gained a reputation as being a good source of omega-3 fatty acids. An oft-cited 1992 analysis, published in the Journal of the American College of Nutrition, found that 100 grams of purslane contained 300-400 mg of omega-3 fats.

But if you search the scientific literature, you'll see that the amount of omega-3 fats in purslane varies a LOT, depending on the variety, the age of the plant, the part of the plant you analyze (leaves, stems, seeds), and the time of harvest. The purslane analyzed in the 1992 study was clearly at the high end of the range. The purslane analyzed at the Nutrient Data Lab appears to be the low end–but is comparable to other published analyses.

The purslane analyzed by the NDL contained only 1mg of fat per gram, or about one tenth of one percent.  With such a low percentage of total fat, it didn't really make sense to break that down further into individual fatty acids.

Is purslane a valuable source of omega-3 or not?

It's true that, compared to other green vegetables, purslane is rich in omega-3 fatty acids. About half the fat in purslane is omega-3. But green vegetables are very low in fat, so that doesn't add up to much.

Let me put this in perspective for you: Even if you were lucky enough to got some high octane purslane like the stuff analyzed by Simopoulos in 1992, you'd need to eat 4 pounds of it to get the amount of ALA found in one tablespoon of flaxseed oil.  Hope you're hungry!

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