Despite clear shifts in the IGF axis, FMD did not differ between diets and did not correlate with IGF axis markers after either intervention.<h4>Conclusions</h4>In adults with T1DM studied under nearly matched glycemia, one week of carbohydrate reduction lowered insulin requirements and shifted the IGF axis in a pattern akin to reduced portal insulin exposure, without detectable changes in conduit artery endothelial function. Here, IGF1 is linked to type 1 diabetes mellitus.