Nutritional Information: Fish

For nutritional purposes, the best way to break down fish into different categories is by how much fat they contain. Fish can be lean, moderately fatty, or fatty.

Lean fish, such as plaice, haddock, and cod, contain less than 5% fat (from 75–125 calories per 100 grams).
Moderately fatty fish, such as halibut, contain between 5% and 10% fat (125–150 calories per 100 grams).
Fatty fish, such as salmon, herring, and mackerel, contain more than 10% fat (over 150 calories per 100 grams).

Note that because one species of fish is fattier than another doesn’t mean it’s less healthful to eat. In fact, fattier fish provide greater benefits than leaner fish because they provide more omega-3s. Numerous studies have demonstrated that omega-3 polyunsaturated fatty acids have a beneficial impact on health. For example, they slow the rate at which blood coagulates, lower blood pressure, and reduce the levels of triglycerides and lipoproteins in the blood—all of which help prevent heart disease.

Other Nutrients in Fish

Regardless of their fat content, fish contain 15–20% so-called complete proteins. Fish are also rich in certain minerals and vitamins, including phosphorus, iodine, fluorine, copper, vitamin A, magnesium, iron, zinc, selenium, and B-complex vitamins. Fatty fish are a very good source of vitamin D (which is not found in the flesh of land animals). Fish is not a source of calcium, unless you consume the bones in canned fish such as salmon or sardines.

Contamination in Fish

Fish are susceptible to pollution. As waterways become increasingly polluted, many species of fish are being contaminated by toxic substances such as DDT (dichlorodiphenyltrichloroethane), PCBs (polychlorinated biphenyls), and mercury. These substances can cause serious illness in humans when present in high concentrations and when large amounts of contaminated foods are consumed.

The level of contamination depends on the age and size of the fish and on its habitat. The older and larger the fish, the more it is likely to be affected by a contaminated environment. As a rule, predatory fish and freshwater fish are more contaminated than saltwater fish. Fatty fish and fish that eat other fish are particularly vulnerable to pollution. For all of these reasons, it’s advisable to limit your consumption of fish caught in polluted waters and fish that are particularly vulnerable to pollution. These fish include: