Does the form of omega-3 you choose matter?
The form matters, but the meal you take omega-3 with matters at least as much: always take ethyl esters with a fatty meal, otherwise a large proportion is poorly absorbed.
The form of omega-3 does matter, but the meal you take it with matters at least as much. Free fatty acids are absorbed best: more than 95% absorption. Triglycerides score 57 to 68%, and ethyl esters only 20 to 21%, but that is with a low-fat meal. Ethyl esters are the form found in many cheaper supplements, recognisable on the label as 'ethyl ester' or 'EE'.
As soon as you take ethyl esters with a fatty meal, absorption triples to around 60%. Triglycerides then rise from 69% to 90%. So if you take a supplement containing ethyl esters, it makes a considerable difference whether you eat 44 grams of fat alongside it or not. The label will say 'triglycerides', 'TG' or 'rTAG' when the more readily absorbed form is used. One thing that does not matter: whether the omega-3 is EPA or DHA individually does not change this comparison.
Krill oil contains omega-3 in the form of phospholipids and, in a study with twelve participants, showed the highest absorption into the blood. However, the difference compared with triglycerides and ethyl esters was not statistically significant, and part of the apparent advantage turned out to come from the fact that krill oil also contains free fatty acids. On this basis, krill oil cannot yet be identified as a proven superior choice. There is also a variant in which omega-3 has already been partially broken down into a smaller structure called monoacylglycerol. This is absorbed comparably well to free fatty acids, but it is not a common supplement form and the research was conducted by researchers at a food company.
What makes the comparison difficult: the studies measure different blood compartments, do not always control for fat intake, and work with small groups. One study found no difference at all between triglycerides and ethyl esters when fat intake was kept equal. Firm conclusions about a ranking are therefore hard to draw. What does hold up: ethyl esters without accompanying fat are a poor combination. The intake strategy is at least as important as the product form you choose. If you are paying more for krill oil or phospholipids because of supposedly proven superior absorption, that extra cost is currently not well supported.
This answer is based on absorption studies from the 1980s and 1990s, two randomised studies (one of which included twelve participants) and three reviews of the overall body of research. The reviews emphasise that most studies had methodological shortcomings: groups that were too small, varying measurement methods and insufficient control of fat intake. The researchers themselves concluded that definitive ranking conclusions about bioavailability are not easy to draw. The evidence for the importance of fat intake when taking ethyl esters is somewhat stronger, but here too large independent studies are lacking.
How much omega-3 with EPA and DHA do you need per day?
There is no fixed omega-3 dose for everyone: for heart protection, around 1 g of EPA+DHA per day is the most studied amount; for inflammatory markers, 1 to 2 g; and during pregnancy, 200 to 300 mg of DHA per day. If you want to support your heart health or are pregnant, always consult a doctor.
Does it matter for your weight whether your calories come from fat or carbohydrates?
In the long term, the ratio of fat versus carbohydrates matters little for your weight, as long as your total calorie intake stays the same. How well you stick to a diet counts for more than which macronutrients it contains.
Does the order in which you eat food and vegetables during a meal matter?
Eating vegetables and/or protein first and carbohydrates last demonstrably blunts the post-meal blood sugar spike, even in healthy people. It is a small adjustment with no downsides that you can simply try out.
Do antioxidant supplements make sense?
For healthy people, antioxidant supplements such as beta-carotene and vitamin E are not useful as protection against cancer or heart disease, and beta-carotene is frankly inadvisable for (ex-)smokers. The only well-supported exception is the AREDS formula for advanced macular degeneration: discuss this with your ophthalmologist.
Does taking omega-3 help you stay healthy for longer?
Omega-3 reliably lowers your blood fats, but the evidence that it makes you live longer or healthier is limited. If you already have heart disease, discuss with your doctor whether omega-3 is worthwhile as a supplement to your treatment.
Does omega-3 protect your skin from sunburn?
Omega-3 may offer some protection against sunburn reactions, but the evidence from good studies is too limited and no proven protective dose is known. Simply continue using sunscreen and regard omega-3 at most as a possible supplement.