Starved fit⁸¹ mutant flies do not show any defects in detecting protein food and display normal preference for tryptone-supplemented (as a source of amino-acids) sucrose food over a sucrose-only food as controls, adult flies of both sexes also show no significant differences in body weight protein or lipid content compared to controls. However, in fit⁸¹ mutant adult females pre-feeding with tryptone leads to significantly weaker suppression of feeding (on standard food) compared to controls (pre-feeding with tryptone does not have a strong suppressive effect on feeding in males, either wild-type of fit⁸¹ mutant), pre-feeding with standard fly food or sucrose exerts normal feeding suppression in both females and males.

In a two-choice assay between sucrose-only and tryptone-supplemented food on unstarved flies, the fit⁸¹ mutants display similar feeding choices as the wild-type controls but the female mutant flies fail to adjust their feeding choice after tryptone pre-feeding and their preference for protein food remains high.