The proposed study is a double blind, randomized, placebo controlled study. The aim of the study is to evaluate the effect of combined growth hormone (GH) treatment \&nutritional formula supplementation versus GH \& placebo on growth parameters in 64 children with Idiopathic Short Stature (ISS) after the second year of GH treatment. Participants will be randomly assigned either to the intervention group or the placebo control group. Randomization for the two study groups will be made in a ratio of 1:1. Both participants and study team will be blinded to the type of treatment that each patient will receive during the study. The randomization will be done according to gender. Participants in the intervention groups will be treated with the study formula and participants in the control group will be treated with a placebo low caloric formula (powder added to water). The study will continue for 6 months of intervention versus active placebo, with additional 6 months (an extension period), in which participants at both groups, the intervention and the placebo, will be offered to continue their participation in the study with the active study supplement.