Influence of diet on the production of a 'lipid-depleting' factor in obese parabiotic rats

When one member of a parabiosed pair of rats is made obese its partner experiences a specific loss of body fat. In this study we determined whether production of the 'lipid-depleting' factor in obese rats was diet specific. One member in each of 30 pairs was tube fed 200% normal intake of high carbohydrate (CHO), high fat corn oil or high fat medium-chain triglyceride diet. Their partners and both members of five control pairs ate CHO diet ad libitum. After 27 d of 200% feeding, in vitro hepatic, adipose and hypothalamic metabolism were measured. Composition of the diet used to induce obesity did not change the response of partners. All non-tube-fed partners had normal food intakes, body protein, hepatic fatty acid synthesis (FAS) and esterification (FAE), palmitate, glucose and β-hydroxybutyrate oxidation. Adipose FAS and FAE were depressed, body fat was halved. Hypothalamic metabolism was not changed. A lipid-depleting agent originating in obese rats specifically inhibits adipose lipogenesis in their partners. Production of this factor does not appear to be influenced by dietary energy source.