Soya bean products. Soya beans (Glycine max, lower right, in bowl) are one of the very best dietary sources of protein. They are also a good source of most of the B-complex vitamins, and the essential minerals iron and potassium. They can be prepared in a variety of ways, including tofu (solid chunks on board), which is a curd used as an alternative to meat, and in a reconstituted and nutritionally supplemented powdered form: soya milk (in glass).