The device, that can be implanted in the intestinal cavity, comprises a reactor comprising a semi-permeable or porous membrane or coating linked to a element for attachment to an intestinal or gastric wall. The reactor can be in the form of a ribbon, a structure having more than two faces or an open structure delimiting a lumen, comprising, or formed from, a semi-permeable or porous membrane. The reactor can also delimit, at least partially with the semi-permeable or porous membrane of same, a closed inner space. The reactor can comprise or carry enzymes or micro-organisms, in particular bacteria or yeast. The reactor is used for generating a chemical reaction with one or more molecules present in the intestine, or for producing one or more biologically active molecules. It can, in particular, be used for consuming sugars, disaccharides and simple sugars or producing essential amino acids or other molecules having a positive effect on the health.