Since letrozole increases serum testosterone and LH at a much higher degree than Arimidex, they explain why no insulin resistance occured with that experiment:
Whereas the 41.3% decline in estradiol we observed is consistent with previous reports with letrozole (21, 22, 35),
the compensatory rise in T was severalfold lower. Letrozole is more abundant than anastrozole in mouse brain tissue after systemic administration (36), providing a potential explanation for the more modest elevation in LH with anastrozole (
31.4% compared with
335%) (35).
This experiment shows that using arimidex with no significant increase in testosterone, and thus decreased aromatase activity, is what causes low concentrations of estrogen in
target tissue which they explain is the cause of the insulin resistance.