AbstractPlasma free fatty acid (FFA), glucose and insulin responses to feeding and fasting were investigated in a sample of two lines of Large White pigs. One line had been selected for nine generations against backfat thickness and for improved growth rate and feed conversion efficiency. The other line had been randomly bred for six generations. No between‐line differences in the plasma constituents were observed in the fed or absorptive state. This is assumed to be the state in which the pigs were reared since they were without food for a maximum of 16 h daily. An increase in the concentration of plasma FFA, indicating the presence of the starved state, only occurred after 16 h without food. It is suggested therefore that changes in these plasma constituents are not important in the reduced fat deposition in the Selection line pigs. In the starved state, however, the Selection line pigs had higher concentrations of plasma FFA than Control line pigs. The relevance of this finding to the differences in body composition is discussed.