The present invention addresses the problem of providing a gastric volume-reducing agent which is safe and can be ingested for a long period. According to the present invention, a gastric volume-reducing agent is provided, which contains, as an active ingredient, at least one type of amino acid selected from the group consisting of glutamine, methionine and phenylalanine. The gastric volume-reducing agent according to the present invention can suppress the relaxation of fundus and/or an upper part of stomach which is adapted to a stretch stimulus to the stomach.本發明係以提供一種安全且能長期攝取的胃容量的減少劑為目的。根據本發明，可提供一種含有選自由麩醯胺酸、甲硫胺酸及苯丙胺酸所成之群中的1種或2種以上之胺基酸作為有效成分的胃容量的減少劑。本發明之胃容量的減少劑可抑制適應胃的伸展刺激之胃底部及/或胃體上部的鬆弛。
