Food intake, growth and tissue amino acid concentrations in lean and obese (ob/ob) mice fed a threonine-imbalanced diet.

Food intake, growth and tissue amino acid concentrations were determined in lean and obese (ob/ob) mice fed a threonine-imbalanced diet. The poorest growth occurred in lean mice fed the imbalanced diet for 7 days; lean mice eating this diet supplemented with the threonine gained three times as much weight as those not receiving the supplement. Weight gains of obese mice consuming the imbalanced diet were not depressed. The obese mice ate more of all but the unsupplemented control diet than did the lean mice. Only lean mice fed a more severely imbalanced diet for 1 day lost weight and decreased their food intake; threonine concentration decreased in blood, brain and muscle of these lean mice but only in brain of the corresponding obese mice. Except for the sum of the concentrations of large neutral amino acids, amino acid levels were low in muscle of control obese mice. When other groups of lean and obese mice were fed a 60% casein diet concentrations of large neutral amino acids in plasma and liver, but not in brain, were 4- and 5-fold greater than in mice fed an 8% casein diet. The results suggest that responses of obese and lean mice to a threonine-imbalanced diet differ.