Does anyone know a good herbal remedy for a slow metabolisim?

Recently I broke my foot in several places and have not yet gained back my "freedom" so to speak. I am in a walking cast and am not allowed to take it off for any length of time. I am not allowed to "walk" or do exercises untiil I can walk without help again. I would like to find an herbal additive or something that I can use. Please only serious posts. Thanks!