Does fish oil break a fast?

Fish oil is pure fat at about 9 calories per gram. A standard 1 g capsule has about 9 calories, two capsules about 18 and three about 27. All three amounts are under the 50-calorie line, which is a common rule of thumb, not an official limit. So capsules keep a weight-loss fast on track.

Liquid fish oil and cod liver oil are a different case. A 5 ml teaspoon of oil weighs about 4.5 g, so it carries about 40 calories. That is close to the line, and two teaspoons go past it. Measure liquid oil with a 5 ml spoon, because a free pour is easy to overdo.

Fish oil has no sugar or starch, so it is safe for a blood-sugar fast. On this site's own four-goal scale, fish oil breaks a fast for autophagy, the strictest goal, because anything with calories counts. Gut rest is grey. The gut has to digest the oil, though a capsule is a small amount.

Taking fish oil with a meal can help your body use it. A small study of men compared fish oil taken with a high-fat meal and a low-fat meal. With the high-fat meal, 90% of the omega-3 fat EPA was absorbed, against 69%. Capsules made as ethyl esters showed the biggest gain, with absorption up about three-fold. That is early evidence. Side effects are usually mild. They include heartburn, nausea, diarrhoea, headache, an unpleasant taste, bad breath and bad-smelling sweat. If they bother you, take the capsules with your first meal.