The fatness (lipid weight at a given liveweight) of a given kind of pig can be varied by feeding. An energy restriction will reduce fatness and a feed of low protein:energy ratio will increase it. Pigs made thin by an energy restriction show “compensatory fattening” when returned to ad libitum feeding. The experiment described here had two purposes: (i) to test if pigs made fat would subsequently show “compensatory thinning” when given a feed of high proteimenergy ratio; it was expected that they would, (ii) To test if pigs would show compensatory protein growth following a period of low protein intake; it was expected that they would not.