Provided are methods, uses and pharmaceutical compositions for inhibition of mammalian alpha-amylase in a subject, with a Helianthamide peptide or a derivative thereof in a biologically effective amount. The subject in need of alpha-amylase inhibition, may have or be at risk of developing one or more of the following: Middleton syndrome; a motility disorder of the gastrointestinal tract; postprandial reactive hypoglycemia; postprandial syndrome; irritable bowel syndrome; diabetes mellitus type 1; diabetes mellitus type 2; pre-diabetes; obesity, dumping syndrome; infant dumping syndrome; polycystic ovary syndrome; steatohepatitis; and viral infection.