An adjustable implant configured to be implanted within or at least partially around an outer surface of a stomach or esophagus is described. The adjustable implant includes a ratchet. The implant further includes an elongate band comprising a shape-memory material, wherein a first end and a second end of the elongate band are configured to couple to the ratchet, such that the band and the ratchet form an assembly having a loop configuration. Activation of the shape-memory material adjusts the band from a first length to a second length as the ratchet permits movement in a first direction of the first end relative to the second end, changing a circumference of the loop configuration.