A while back I wrote a blog about the different kinds of fats (Omega-3? Trans-fat? Saturated fat? What does it all mean?). It’s a little technical, but it had to be to explain the meaning of those terms. What I didn’t talk about then was the relevance of the types of fats in our diet. One kind of fat that is very frequently discussed with regard to human health is the omega-3 type of fat, a polyunsaturated fat. Omega-3 fatty acids are ‘essential’, meaning that we must take them in through our diet, as the body cannot make them.
There are different kinds of omega-3 fatty acids within the ‘family’. Their differences lie in the length of the molecule and the number of double bonds (i. e. how unsaturated they are). The ones involved in human metabolism are alpha-linolenic acid (ALA) – the shortest omega-3 fatty acid molecule – and eicosapentanoic acid (EPA) and docosahexanoic acid (DHA), which are much longer and more unsaturated.
While the body cannot make omega-3 fats, it can convert them – i. e. turn ALA into EPA or DHA -, but unfortunately it is not very good at it: under ideal conditions only approx. 5% of the ALA we eat gets converted, and more often than not conditions are not ideal. Stress, medication, disease, age and even gender (women convert better than men) affect conversion, but most of all, it is hampered by high levels of omega-6 fats. Omega-6 fats are also essential, but they are much, much more abundant in the Western diet than omega-3. However, both the basic omega-6 fat (linoleic acid, LA) and the basic omega-3 fat (ALA) compete for the same enzyme to get them up to the next rung of the ladder. If there is abundant omega-6, it’ll hog the enzyme and omega-3 barely stands a chance to use it.
In our caveman days, the ratio of omega-6:omega-3 fats in our diet was about 1:1. Today, in the typical Western diet, it can be 10:1, but even as high as 30:1. There are functional tests today (blood spot) you can use to find out what your ratio is. A recent study has compiled data on omega-3 – or rather EPA and DHA – blood levels in the world population and drawn up this handy map:
It shows that EPA/DHA levels are low or very low in most of the countries the researchers had data for. Only very few regions had adequate levels of omega-3 fats. Like other countries where most people have adopted a modern Western diet, the UK is among those with very low levels.
Why does it matter?
EPA and DHA have a multitude of functions in the body, the most important one is that they are part of cell membranes. Every single cell in our body needs polyunsaturated fatty acids (as well as mono- and saturated ones, to be fair) to ensure the membranes fluid structure. Long-chain omega-3 fats are used in the management of a myriad of health issues.
Given the involvement of inflammation in chronic disease, another important benefit of EPA and DHA are their anti-inflammatory properties. Both omega-6 and omega-3 fats are further converted substances called eicosanoids, which in the case of omega-6 can be pro-inflammatory or anti-inflammatory, while eicosanoids derived from omega-3 fats can only be anti-inflammatory.
DHA is one of the main components of the brain and is crucial not just for child development (both ante- and postnatal) but also for the health of the adult human brain. Fish oils in particular are used in the management of mental health issues, such as anxiety and depression as well as the prevention of dementia. The most robust body of evidence supports the role of omega-3 fats in heart health: they have been found to offer protection from congestive heart failure, been shown to lower blood pressure and triglycerides and to help prevent chest pain and the build-up of arterial plaques.
Dr. Manfred Eggersdorfer, Senior Vice President, Nutrition Science and Advocacy at DSM Nutritional Products and Professor of Healthy Ageing at the University Medical Center Groningen says: “PUFAs, and EPA and DHA in particular, have long been associated with decreased risk of cardiovascular mortality and cognitive decline. The conclusions of this paper [click on the map above] highlight that a significant proportion of the population are at increased risk of chronic disease due to low omega-3 PUFA status.”
Where do you find them?
The best sources for plant-based omega-3 fats are milled linseeds (flaxseeds), chia seeds, walnuts, and hemp seeds. None of these contain EPA or DHA though, only ALA. The best known source for EPA and DHA is oily fish, however the fish doesn’t produce them but gets them from the algae – mainly microalgae – it consumes. Microalgae can be commercially grown and are now being used for the production of vegetarian EPA/DHA supplements. Brown algae (kelp) is also a source of plant-based EPA.
The main animal sources are coldwater fish (pilchards, sardines, herring, mackerel, salmon, tuna) and omega-3 eggs. The omega-3 concentration in those eggs is higher as the hens are fed greens and insects rather than grains.
It is ironic that blood levels should be low in the UK – a country surrounded by the sea. However, there are of course environmental considerations: fish stocks around the world are running low, and many – not just vegetarians and vegans – avoid fish for ethical reasons. Moreover, the oceans are contaminated with mercury, a toxic metal that accumulates in the fatty tissues of fish. Contamination is higher in larger, predatory fish, particularly tuna.
Krill, a small crustacean that also contains EPA and DHA is now used for many omega-3 supplements. While krill is not endangered, it is a food source for other marine animals that are, such as whales. If you buy fish and/or fish and krill oil, make sure that it has the seal of the Marine Stewardship Council. Better still: Find a supplement made from algae.
To maximise your own body’s conversion of omega-3 fats, make sure to incorporate plant sources into your diet and limit sources of omega-6 (think: grains, processed foods, baked goods). If you suffer from any chronic disease or are pregnant, plant omega-3 is not going to be enough though, unless you use a plant-based EPA/DHA supplement.