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Food · Animal Foods · Fish
food source · 5
Salmon stores its oil in its muscle, so the fillet you eat carries the long-chain omega-3 fats EPA and DHA itself: about 1.8–2.5 g per 100 g of farmed Atlantic salmon.
Mechanism · Why the oil is in the flesh
Salmon and its relatives store oil in the muscles they swim with. Cod stores its oil in the liver instead, which is why cod-liver oil carries omega-3 and vitamin D while a cod fillet has almost none. Salmon fat is woven between the muscle fibers and cannot be trimmed away; cutting off the layer under the skin throws out the most valuable part of the fish.
Evidence · Eating fish is not taking fish oil
Farmed Atlantic salmon has about 1.8–2.5 g of EPA and DHA per 100 g. The same double bonds that keep cell membranes supple in cold water also make this fat sensitive to long, high heat, so steaming it or searing it lightly until just pink in the center keeps more of it. Cochrane 2020 pooled 86 randomized trials with more than 160,000 people, mostly of fish-oil capsules, and found with high certainty that taking more omega-3 has little or no effect on deaths or cardiovascular events. But it judged capsules, not eating whole fish: the benefits of eating fish come mainly from observational studies, and a piece of fish also brings protein, vitamin D, selenium and B12, and often replaces a serving of red meat.
Vitamin D dissolves in oil and travels with fat. Salmon stores its oil in the flesh, so the fish itself carries a useful amount of vitamin D: about 250–650 IU per 100 g of farmed Atlantic salmon.
Mechanism · Vitamin D travels with the oil
Vitamin D dissolves in oil, so it sits wherever the fat is. Salmon stores its oil in muscle, so the vitamin D is in the fillet you eat; cod stores its oil in the liver, so its flesh has almost none. What you eat is only raw material, which the liver and then the kidney each have to process before it becomes the active form.
Numbers · A rare food source in winter
Farmed Atlantic salmon has about 250–650 IU of vitamin D per 100 g, and wild salmon usually has more. In a high-latitude winter the skin makes almost no vitamin D, and few natural foods supply a useful amount; fatty fish are one of them.
Salmon is a good source of B12: farmed Atlantic salmon has about 2.5–3 μg per 100 g, enough to cover most adults' recommended amount for a day (2.4 μg).
Mechanism · The fish does not make B12
Only bacteria and archaea make B12. Microbes in the sea make it and it builds up step by step along the food chain, so salmon concentrates B12 rather than producing it. In people short of stomach acid or intrinsic factor, none of the amount on the plate gets absorbed.
Numbers · One serving covers a day
Salmon has about 2.5–3 μg of B12 per 100 g, while the US adult Recommended Dietary Allowance (RDA) is only 2.4 μg a day. It comes in the same piece of fish as the omega-3 and vitamin D, not as a separate item.
Sea fish are a good source of selenium, and salmon is no exception. Selenium is built into the active site of a group of antioxidant enzymes, a part those enzymes need in order to work.
Mechanism · The screw in the enzyme
Selenium is not an antioxidant itself but a part fitted into the active site of a group of enzymes: the enzymes do the work, and selenium is the screw that lets them. The selenium in sea fish is steadier than in grain, because it depends less on the soil where the food was grown.
Safety · Selenium is no excuse for mercury
Selenium binds mercury, and by the chemistry it can offset a little of the effect of the trace mercury in sea fish; but the selenium is used up in the process and the offset is only partial, so do not treat it as a reason to stop worrying about high-mercury fish.
Salmon is complete protein. Its fat is woven through the muscle and cannot be removed, so the protein arrives together with fat rich in omega-3.
Mechanism · Protein and good fat come together
Salmon has all nine essential amino acids and is highly digestible, in the same class as lean beef and chicken breast. Its fat is woven into the muscle, so every bite carries protein together with EPA and DHA, and the two cannot be separated.
Numbers · The protein in a fillet
Cooked farmed Atlantic salmon has about 22–25 g of protein and 12–13 g of fat per 100 g. A typical fillet weighs about 150–180 g, which gives more than 35 g of protein in one meal.