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Food · Animal Foods · Fish
food source · 3
White fish has almost no fat, so nearly all of its calories come from protein, which makes it one of the most protein-dense animal foods per calorie.
Mechanism · What is special is the denominator
White fish has almost no carbohydrate and almost no fat, so protein is left to fill the calorie column. Its high protein density does not come from an unusually large amount of protein but from how little of everything else it has. It is complete protein, with enough of all nine essential amino acids and plenty of leucine. Cooking mainly removes water, and the total protein barely changes.
Numbers · Protein and calories in cod
Raw cod has about 82 kcal, about 17.8 g of protein and about 0.7 g of fat per 100 g. A 150 g serving of cooked cod gives about 30 g of protein for 130–150 kcal; the same protein from lean pork costs more than 200 kcal. Shop and log food by raw weight, because mixing raw and cooked figures overcounts.
Seafood is generally a good source of B12. White fish is not the richest seafood, but it is mild, cheap and the easiest to eat every day, and one serving meets more than half of a day's need.
Mechanism · Only microbes make it
Only bacteria and archaea can make B12. The sea is full of B12-making microbes, and B12 passes up the food chain step by step, so seafood is generally a good source while plant foods have almost none. Once eaten, it still has to pass the three steps of stomach acid, intrinsic factor and the end of the small intestine.
Numbers · The B12 in a serving of cod
Raw cod has about 0.9 µg of B12 per 100 g, more by weight once cooking drives off water, and one serving meets more than half of a day's need. It is lower than shellfish such as oysters and clams, but it is mild, cheap and easy to eat every day, and something you can keep eating is worth more than the highest number.
Iodine is dissolved in seawater and passes up the food chain, so sea fish are one source of it. The amount varies with species and waters, so eating seafood regularly is a more practical way to cover iodine than counting on any one fish.
nih-ods-iodineMechanism · Iodine washed into the sea
Most of the earth's iodine has been washed into the sea by rain. Algae concentrate it from seawater and it passes up the food chain, so sea fish, kelp and nori contain iodine while freshwater fish have almost none. Iodine is a building block of the thyroid hormone molecule, and without it the hormone cannot be made.
In practice · Cover iodine by eating seafood often
The iodine in white fish varies with species and waters, and neither is fixed, so it is not worth counting fish by fish; the habit of eating seafood often is what covers it. Vitamin D is not white fish's strength either: raw cod has about 0.9 µg per 100 g against about 11 µg in salmon, a tenfold gap.
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