What are the negative side effects of phenylketonurics and soy lecithin?

Phenylketonurics is likely safe for adults when consumed in amounts normally contained in foods; soy lecithin is also safe for adults in normal quantities but may have mild side effects, such as nausea, diarrhea, abdominal pain and fullness. Lecithin is not recommended for pregnant women, according to WebMD.

Phenylalanine can build up to high levels in some people with a preexistent illness called Phenylketonuria. People with this disorder can develop serious health issues and should avoid phenylalanine. Lecithin is a food additive that has healthful qualities. It is used to treat memory disorders and organ diseases. Lecithin is naturally obtained in egg yolks and soybeans, according to WebMD.