What compounds found in raw green beans does older advice suggest might cause mild poisoning?

Lectins and Phytohaemagglutinin

When discussing the consumption of raw green beans, there is a historical caution stemming from the presence of certain naturally occurring proteins. Specifically, older advice often pointed to the presence of lectins and Phytohaemagglutinin as substances that could render raw common snap beans mildly poisonous if consumed without cooking. While modern testing suggests that immature green beans, distinct from broader types like lima or fava beans, are often safe raw without ill effects, acknowledging these compounds explains why cooking is generally recommended for standard preparation. The raw experience, if pursued, is characterized by bitterness and crunch, elements that are eliminated through heat treatment.