One major area of Van Soest’s research involved developing a nutritionally relevant fiber analysis. Van Soest’s detergent analysis gave researchers a way to precisely separate the chemical components of feeds into three categories: parts that were digestible to all animals; indigestible without fermentation; and completely indigestible. This work offered new ways to measure chemical compositions and the exact energy output of feeds. Van Soest’s detergent analysis has been expanded and adopted worldwide, replacing a less accurate system that had been used since the 1860s. Further, his work in fiber chemistry was adopted by human nutritionists and researchers interested in the effects of dietary fiber on gut health and obesity.

Van Soest’s numerous honors included awards from the American Dairy Science Association and the American Society of Animal Science, election as a fellow of the American Institute of Nutrition, and an honorary doctorate from the University of Milan in 1992.