 Slow lorises have an unusually low basal metabolic rate , about 40 % of the typical value for placental mammals of their size , comparable to that of sloths . Since they consume a relatively high @-@ calorie diet that is available year @-@ round , it has been proposed that this slow metabolism is due primarily to the need to eliminate toxic compounds from their food . For example , slow lorises can feed on Gluta bark , which may be fatal to humans . 
