Bitterness is of interest to those who study evolution, as well as various health researchers. Many naturally bitter compounds are toxic. The ability to detect bitter-tasting, toxic compounds at low thresholds may have a protective function, but some test have not confirmed this. Plant leaves often contain toxic compounds, and among leaf-eating primates there is a tendency to prefer immature leaves. Young leaves tend to be higher in protein and lower in fiber and poisons than mature leaves. Amongst humans, various food processing techniques are used worldwide to detoxify otherwise inedible foods and make them palatable.