Consumption of oily fish is sporadic, whereas controlled intervention studies of n–3 (ω-3) fatty acids usually provide capsules containing eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) as a daily dose. This methodologic study explored whether there are differences in the short-, medium-, and long-term incorporation of EPA and DHA into blood plasma and cells with the provision of identical amounts of EPA and DHA, equivalent to 2 oily fish servings per week (or 6.54 g/wk EPA and DHA), either intermittently (i.e., 1 portion twice per week) or continuously (i.e., divided into daily amounts). The study was part of a randomized, double-blind controlled intervention lasting 12 mo, with participants stratified by age and sex. There were 5 intervention groups, 2 of which are reported here: the 2 intermittent portions (2I) and 2 continuous portions (2C) groups. EPA and DHA were measured in plasma phosphatidylcholine, platelets, and blood mononuclear cells (MNCs) at 9 time points. Sixty-five participants completed the study (2I group, n = 30, mean age of 49.2 y; 2C group, n = 35, mean age of 50.6 y). The incorporation pattern over the 12-mo intervention was different between the 2 groups in all samples (P < 0.0001, time × treatment interaction). At the end of the 12-mo intervention, the 2C group showed higher EPA, DHA, and EPA + DHA in platelets (all P < 0.01) and higher EPA and EPA + DHA in MNCs (both P < 0.05) compared with the 2I group. No significant differences were shown for plasma phosphatidylcholine EPA (P = 0.1), DHA (P = 0.15), EPA + DHA (P = 0.07), or MNC DHA (P = 0.06). In conclusion, the pattern of consumption does affect the incorporation of EPA and DHA into cells used as biomarkers of intake. The differences identified here need to be considered in the design of studies and when extrapolating results from continuous capsule-based intervention studies to dietary guidelines for oily fish consumption.
Alex's notes: A study in 2012 found that plasma phosphatidylcholine is the most suitable biomarker for acute changes in EPA/DHA, while platelets and mononuclear cells are better suited for habitual intake. Given the study duration, the differences between groups in the platelets and mononuclear cells are worth noting. The more often you consume omega-3s, the greater the effect in your body, even when overall intake is equated. This definitely gives support to the notion of daily fish oil supplementation, but overall consumption must be monitored.
Overconsuming omega-3s has many of the same negative health consequences as overconsuming omega-6s. For instance, one study found that 3g of fish oil daily in persons with metabolic syndrome actually increased LDL-C and insulin resistance after just 45 days. Another study found that oxidative damage increases as omega-3 intake increases, and 6g of omega-3 fatty acids daily for six weeks increased lipid peroxides. What has happened is that individuals fall for reductionist thinking and reason that if some fish oil is good, more must be better. NO!
All the above taken into consideration, it is paramount to consume fatty fish at least 1-2x per week, but it is also wise to supplement fish oil on days when you don't eat the fatty fish. Just don't overdo it. 1g/day of EPA+DHA should be more than enough to reap the benefits without risk of harm, and only on days when you don't eat fatty fish (salmon, sardines, makeral).