The combination of fish and leafy vegetables, such as spinach, may in theory be toxic. There is no indication that the combination of spinach and salmon is especially risky.

From a toxicological point of view the combination of fish with spinach is not recommended. Fish contains so-called secondary amines, whereas spinach contains nitrate. The nitrate may be converted largely to nitrite. Nitrite and secondary amines may react to form nitrosamines. Nitrosamines consist of a large group of compounds, some of which are considered carcinogenic. Animal studies have shown that some nitrosamines cause cancer of the liver or stomach.

Although laboratory studies have shown that nitrosamines may be formed, there is no epidemiological (population research) proof that there is a relation between certain cancers and the intake of leafy vegetables with or without fish. One of the reasons for the apparent lack of evidence and probably of any connection at all between these cancers and a combination of the two food items may be that leafy vegetables also contain vitamin C, which prevents the formation of nitrite and thus of nitrosamines.

In conclusion it can thus be stated that there is a theoretical risk, but that there is no proof that there is an actual risk for the individual or population.