Your body also needs omega-6s, another type of fatty acid, to function properly and prevent disease. Unfortunately, these are found in much more abundance than omega-3s in the standard American diet, although your body craves a 1:1 ratio to keep inflammation low. Most modern diets contain a ratio closer to 20:1 or 30:1 omega-6 to omega-3 fatty acids.
Not all forms of fish oil may be equally digestible. Of four studies that compare bioavailability of the glyceryl ester form of fish oil vs. the ethyl ester form, two have concluded the natural glyceryl ester form is better, and the other two studies did not find a significant difference. No studies have shown the ethyl ester form to be superior, although it is cheaper to manufacture.
The most extensive data of the effect of fish oil on lipoprotein subfractions are based on trials performed before the widespread use of statins. This data were aggregated over a decade ago in a meta-analysis of 16 randomized trials including over 1500 patients.17 In this analysis, low-density lipoprotein (LDL) was increased by an average of 5% and high-density lipoprotein was marginally changed. Although a shift toward less atherogenic, larger and more buoyant LDL particle composition has been shown,74 this has been offset by the observation that the number of apolipoprotein B 100 particles increases and may be more susceptible to oxidation.75 Increased conversion of remnant particles (intermediate density lipoprotein) to LDL has also been observed.76
A lot of the benefit of fish oil seems to come from the omega-3 fatty acids that it contains. Interestingly, the body does not produce its own omega-3 fatty acids. Nor can the body make omega-3 fatty acids from omega-6 fatty acids, which are common in the Western diet. A lot of research has been done on EPA and DHA, two types of omega-3 acids that are often included in fish oil supplements.