Fish oil supplements with over 95% re-esterified triglycerides (a type of fat form) seem to get more omega-3s into your blood cells after 16 weeks than those with less than 70%, so this might be a good sign of a better-quality supplement.

Taking high-quality fish oil pills with more of a certain form (called re-esterified triglycerides) leads to higher levels of a healthy fat called DPA in your blood cells after four months, compared to lower-quality ones.

If you're a healthy young adult, taking a high-purity fish oil supplement might help your body absorb more of the good omega-3s (like EPA and DHA) into your red blood cells compared to a lower-purity version—even if the difference in dose is pretty small.

If you're a healthy young adult, taking a high-purity fish oil supplement might improve your blood fat levels faster than a lower-purity one — and you could see changes in just four weeks.

Your body absorbs omega-3s from fish oil better depending on the form they're in — free fatty acids are easiest to absorb, triglycerides are okay, and ethyl esters are the hardest.