Glycemic index of lactose is ~68 (bread control) and the insulin index is 50 (bread control)
the raised insulin of the milk is not a cause of the lactose itself, but a function of the protein(or fat) as well.
Ostman EM et al. Inconsistency between glycemic and insulinemic responses to
regular and fermented milk products. Am J Clin Nutr 2001;74:96-100