Reversible obesity and plasma fat metabolites.

Rats were made to overeat and gain weight (about 50 g) by long-acting protamine zinc insulin (PZI) treatment. When the PZI treatment was stopped, the rats ate much less than normal for at least seven days. During recovery from PZI-induced obesity, negative correlations were observed between food intake and plasma levels of the fat metabolites, free fatty acids, glycerol, and ketone bodies. A similar but smaller effect was observed during recovery from dietary obesity (about 15 g). The plasma fat metabolites may be the blood-borne signals which suppress hunger under these conditions.