Soy protein concentrate is the clean dehulled soybean seeds that have had most of the oil and water soluble non-protein constituents removed. (AAFCO, 2003) Soy protein is much harder to digest than meat, and is considered a cheap, poor quality protein filler. Soy is highly allergenic, causing problems for many animals and contains some enzyme inhibitors which impeded protein digestion. Most soy is also genetically modified (see GM), which makes its long term effects impossible to predict.