The present invention relates to an alpha -amylase activity inhibitor containing, as an effective component, polyphenols obtained through the following process: guava leaves and/or guava fruit are subjected to extraction with one or more solvents selected from among water and hydrophilic solvents； the resultant extract is subjected to ultrafiltration, to thereby remove substances having a molecular weight of less than 5,000； the remaining fraction is subjected to the butyl support hydrophobic chromatography. The elution (flow rate: 1 mL/min) of the sample was accomplished with the pH gradient by use of sodium dihydrogenphosphate and sodium phosphate solution (0.02 mol/L) and a fraction of the eluted substance is recovered, which fraction corresponds to the third single peak of an elution curve which is obtained when the absorbance of the substance is measured at 260 nm. The present invention also relates to an alpha -amylase activity inhibitor containing, as an effective component, polyphenols having specific physicochemical properties, and to food and beverages containing the alpha -amylase activity inhibitor. The alpha -amylase activity inhibitor of the present invention exhibits remarkably excellent alpha -amylase inhibitory activity as compared with guava extract. Accordingly, food and beverages containing the alpha -amylase activity inhibitor are diet food and beverages suitable for people of high blood-sugar level or hyderlipidemia.
