Image source: https://www.eufic.org/en/whats-in-food/article/the-importance-of-omega-3-and-omega-6-fatty-acids
There are two fats that humans have to eat as the body cannot make them and they are required for specific functions. They are called omega-3 (ω-3) and omega-6 (ω-6) and known as essential fatty acids (EFA’s) for this reason. They are both polyunsaturated fatty acids (PUFA’s) which means that they have more than one double bond between their carbon back bone. They get their name from the carbon number where their first double bond appears (see pic).
In the diet omega-3 is found in flax, hemp, pumpkin and chia seeds as well as walnuts. The end products of omega-3 (ALA) that the body requires are called EPA and DHA. Fish already contains both which is why it is such a good source, as the body doesn’t need to convert it. The conversion from other sources is very small and many people struggle with it, hence the oily fish recommendation.
Omega-6 is found in vegetable oils from seeds of corn, sunflower, safflower, cotton and soybeans. It is also found in evening primrose oil, borage, starflower and blackcurrant oils. It is converted to a downstream product known as arachidonic acid (AA). This end product (AA) is freely available in meat, egg and dairy products.
Our intake of omega-6 tends to exceed omega-3 considerably due to the nature of most people’s diets and the relatively recent availability of vegetable and sunflower cooking oils. My parents are over 80 but my mum can still remember how she queued up in the grocers to buy a slab of butter, wrapped in greaseproof paper. Most processed foods and ready-made dressings, sauces and jars also contain omega-6.
Research scientist Simopoulos (2002) believes we historically consumed equal amounts of omega-3 and omega-6, a 1:1 ratio. We now consume 15-16.7 times as much omega-6.
Omega-3 and omega-6 fatty acids are however both important components of cell membranes. During the conversion process they produce downstream products (eicosanoids) which regulate our inflammatory responses. Omega-3 eicosanoids are known to have anti-inflammatory effects. The eicosanoids from omega-3 tend to be more anti-inflammatory and anti-coagulatory than omega-6, which produces both inflammatory and anti-inflammatory versions.
Omega-3 and omega-6 both utilise the same conversion enzyme (delta-6-desaturase) so theories have arisen that one process will deprive the other. A high omega-6 intake is thought to reduce the availability of this enzyme and so diminish our omega-3 conversion. This theory and the concept of an “ideal” ratio in the diet is contested but it is generally thought that a ratio of 4:1 (ω-6: ω-3) is optimum.
The European Food Safety Authority concluded that 250 mg a day of EPA and DHA was adequate. They also found that European intake was too low at between 20-40 mg per day for EPA and less than 100-130 mg per day for DHA.
It’s kind of difficult to think about ratio’s when you are out shopping or planning your menus, so this is the way I tend to advise clients. Providing your digestion is good then generally you can obtain enough EPA and DHA by consuming oily fish 2-3 times per week. Otherwise supplementation is likely the best option.
References
https://pubmed.ncbi.nlm.nih.gov/12442909
https://efsa.onlinelibrary.wiley.com/doi/10.2903/j.efsa.2010.1461
https://www.eufic.org/en/whats-in-food/article/the-importance-of-omega-3-and-omega-6-fatty-acids
