Among the various dietary sugars, oligosaccharides of the raffinose family have a definite antinutritive effect. These sugars (raffinose, stachyose, and verbascose) occur in substantial amounts in mature legume seeds and comprise 30% to 80% of the total soluble sugars. They contain a-galactosidoglucose and a-galactosidogalactose bonds. The human gastrointestinal (GI) tract does not possess enzymes capable to catalyze compounds of this type. The mammalian invertase (a saccharide-splitting enzyme) is an a-glucosidase. Also, the raffinose family sugars are unable to pass through the intestinal mucosal wall. Consequently, the microflora in the lower intestinal tract metabolize these sugars to produce flatus (gas or air).

The accumulation of flatus in the intestinal tract results in discomfort, abdominal rumblings, cramps, pain, and diarrhea and is characterized by the production of hydrogen, carbon dioxide, and small amounts of methane gas. Sugars of the raffinose family are believed to be largely responsible for the problem of flatulence after consumption of diets containing beans and other legumes.