Almost all fish is very low in cholesterol and fat. The fat is usually only about 1 percent, and of that small amount, only about 10 percent is saturated. Most fish are composed of 70 percent water and 10 to 20 percent protein, plus traces of minerals; vitamins A, B, and D; glucides; and lipids. Calorie content is approximately 160 per 100 grams (about 4 ounces) for fatty fish and 70 calories per 100 grams (about 4 ounces) for lean fish.
Some fish may even promote good health. In fact, it has been known for some time that diets high in fish oils, such as those of Scandinavians, Japanese, and Inuit, seem to be coupled with low rates of heart disease and many cancers. Studies suggest that it is the omega-3 fatty acids in fish that are the source of this benefit. Fatty fish such as salmon, mackerel, and tuna, seem to be the most beneficial.