The main ingredients of traditional Japanese sushi, raw fish and rice, are naturally low in fat, high in protein, carbohydrates, vitamins, and minerals. The same may not be said categorically of Western-style sushi, which increasingly features non-traditional ingredients such as mayonnaise, avocado, and cream cheese.
Most seafood is naturally low in fat, with fats found in seafood predominately being unsaturated and thus containing relatively high levels of Omega-3. Since sushi is often served raw, no cooking fat is introduced during its preparation. Some non-traditional ingredients such as cream cheese and mayonnaise that are sometimes found in Western-style sushi dishes can add significant amounts of fat to a traditionally lean dish.
Fish, tofu, seafood, egg, and many other sushi fillings, contain high levels of protein. Imitation meat such as krab stick may be lower in protein and other nutrition than their natural, unprocessed counterparts.
Vitamins and minerals are found in much of the seafood and vegetables used for sushi. The nutritional content is dependent on the ingredients used. For example, shrimp is high in calcium and iodine, whereas salmon is rich in Vitamin D. The gari and nori used to make sushi are rich in both nutrients. Other vegetables wrapped within the sushi also offer various vitamins and minerals.
Carbohydrates are found in the rice and the vegetables. Certain non-traditional ingredients can raise the carbohydrate level quite high, as with the fat level.
Some large fish, such as tuna (especially bluefin), can harbor high levels of mercury. This is due to the tuna's position at the top of the food chain (among sea creatures). Thus, tuna can lead to mercury poisoning when consumed in large quantity. The FDA recommends, for certain groups (women who might get pregnant, pregnant women, nursing mothers and young children), eating a maximum of 12 ounces a week of a variety of fish and shellfish.
Parasite infection by raw fish involves mainly three kinds of parasites: Clonorchis sinensis (a trematode/fluke), Anisakis (a nematode/roundworm) and Diphyllobothrium (a cestode/tapeworm). Infection risk of anisakis is particularly higher in fish which may live in a river such as salmon (shake) in Salmonidae, and mackerel (saba). Such parasite infections can generally be avoided by boiling, burning, preserving in salt or vinegar, or freezing overnight.
For the above reasons, the EU regulations forbids the use of fresh raw fish, and must be frozen at temperatures below −20 °C in all parts of the product for no less than 24 hours.
Some forms of sushi, notably those containing pufferfish fugu and some kinds of shellfish, can cause severe poisoning if not prepared properly. Particularly, fugu has a lethal dose of tetrodotoxin in its internal organs and must be prepared by a licensed fugu chef who has passed the prefectural examination in Japan. The licensing examination process consists of a written test, a fish-identification test, and a practical test, preparing and eating the fish. Only about 35 percent of the applicants pass, and in rare cases, death results.[not in citation given] The Emperor of Japan is forbidden to eat fugu, as it is considered too risky.