Soya, Human Nutrition and Health

Popular advice for healthy diets that may promote health and longevity include the daily consumption of at least three servings of fruits or vegetables and the variation of foods to include items derived from different plants and those plants should belong to different botanical families (Thompson H.J. et al., 1999). Ancient civilisations in the Middle East and in America included grain legumes and cereals in well-balanced diets. In the funeral offerings found in the Egyptian pyramids various legume seeds were present, including lentils and grass pea. Apparently, legumes were a food of special consideration to be offered to kings, in contrast to the present day reputation of being the meat of the poor, with 75% of all legumes now being produced in developing countries. Excavations of ancient settlements indicate the use of both cereals and legumes (Mahler-Slasky & Kislev, 2010). A well balanced food basket promoting health and strength may have given an evolutionary advantage. The benefits of legume cultivation for soil fertility were already recognised in the 4th century BC (Flint-Hamilton, 1999). Legumes are important factors in the natural cycle of nitrogen, being able to fix atmospheric nitrogen in symbiosis with Rhizobium bacteria. This enables the leguminous plants to thrive on poor soil, which makes them essential partners in the maintenance of soil fertility, and to produce protein-rich seeds. However, maintenance of optimum rates of nitrogen fixation requires continued attention by plant breeders (Provorov & Tikhonovich, 2003). Legumes are also unusually diverse in their defence against predators by producing a large array of secondary metabolites forming their chemical armoury. Those metabolites include anti-nutrients such as inhibitors of digestion and compounds interfering with predator’s metabolism reaching as far as brain function and hormonal control (Rozan et al., 2000). Interestingly, some of these metabolites are beneficial by their inhibition of human cancer cells or by antioxidant activity that can delay ageing. Although legumes have many beneficial properties, they are not a well balanced food by themselves because of deficiencies in some essential amino acids, and should not be the sole component of the food basket. In combination with cereals that are richer in those essential amino acids which are deficient in legumes such as methionine, cysteine and tryptophan, legumes are beneficial for human health and for the world’s ecology. The optimum protein quality is approximated when 60-70% cereals are mixed with 30-40% cooked legumes. This would produce a combined quality of protein comparable with meat (Bressani & Elias, 1974).