Abstract: The buckwheat extract comprises a extract of buckwheat which are enriched in D-fagomine and including 3,4-di-epifagomine, a process for their preparation, pharmaceutical or veterinary compositions, dietary supplements or functional foods containing them, their use alone or in combination with saccharide, an iminocyclitol or probiotics, as a blood glucose levels controlling agent reducing the post-prandial glucose levels, as well as the buckwheat extract for use in the prevention and/or coadjuvant treatment of microbiota imbalance, that reduces the adhesion of some potentially harmful microorganism in the microbiota and therefore increasing the resistance to disease.