There is an interesting conversation afoot on StrongLifts.com following Mehdi’s post on The Only Supplements You Need to Build Muscle and Strength. One of those supplements is fish oil, which has been shown to reduce inflammation, decrease body fat, ease soreness, and lower cholesterol. There’s no RDI standard for fish oil, but about 1 Tablespoon per day seems to be the consensus among nutritionists.

The thing is, vegetarians like me don’t eat fish oil. The good news, we’ve been told, is that flax oil is a great source of omega-3’s. 100 grams of flax oil contains 20.3 grams of omega-3 fatty; this is heaps more than the 3.2 grams per 100 grams of salmon, the much lauded king of omega-3.

But it turns out, not all omega-3’s are created equal – the omega-3 molecule in flax is different from that in salmon. Let’s get a little sciencey for a second…

In simple terms, a fatty acid is a chain of carbon. Omega-3s are a specific family of fatty acid whose first double bond occurs after the third carbon atom (hence the name). There are several types of omega-3 fats, all of which differ in their number of carbon atoms and double bonds. Those that are important to health are: ALA, EPA and DHA.

The ones we ultimately want are DHAs – that’s the stuff found in our brain, retina, and heart and are responsible for all the purported benefits of omega-3. Our body can convert ALA to EPA, and EPA to DHA, so you would think that if you ate enough ALA in plant-based food, then you’d get enough DHA.

The problem is, the conversion rate from ALA to DHA in humans is fairly low: a 1998 study observed 4%, while a 2005 study found less than 0.1%. Both studies show that the conversion rate is highly variable among individuals.

Whether this is a real issue depends on how much DHA the body really needs. For average individuals without chronic heart disease, The American Heart Association recommends eating fish twice a week – that’s equivalent to about 500mg of EPA+DHA per day. So on a good day, you’d need to eat over 2 Tbsp of flax oil to get the recommended serving, or over 5 Tbsp of flax seeds (good luck with that).

To complicate matters, linoleic acid (LA), an omega-6 fat found in many vegetarian foods, interferes with the conversion of ALA to DHA. So if you’re a vegetarian or vegan, how can you ensure that you’re getting enough omega-3? The Vegetarian Society has a few suggestions:

1. Make sure you include a good source of ALA in your diet
2. Replace fats high in omega 6 oils, such as sunflower oil or corn oil, with fats higher in monounsaturated fats, such as olive oil or rape seed oil which do not disrupt the formation of EPA and DHA.
3. Eat other foods high in ALA: broccoli has 0.13g per 100g, cabbage 0.11g per 100g … walnuts and tofu are also good sources but are comparably high in LA.

Damn, and here I’ve been eating loads of walnuts because I knew they had lots of omega-3’s. I’ve been duped! Right, so what have I learned?

• The human body is a fascinating chemistry lab
• Science is hard (still)
• My tsp of flax seed per day is probably insufficient
• The internet is rife with dubious health claims – but we knew that already

Open questions:

• What are the consequences to not getting enough DHA?
• What are the health benefits of ALA?

If you want to read more about Omega-3s, check out the articles at the DHA/EPA Omega-3 Institute.