The IRS1 gene encodes a protein, insulin receptor substrate 1. It plays a key role in transmitting signals from the insulin and insulin-like growth factor-1 (IGF-1) receptors to intracellular pathways.
If you carry the C-allele, you are predisposed to insulin resistance, impaired insulin sensitivity, hyperinsulinemia, and an increased risk for type 2 diabetes. It is important for you to look at your genetic variations for PPARG, TCF7L2, and FTO as this could compound or increase your risk for the above.
If you carry the T-allele in this gene, you'll likely have a decreased risk of insulin resistance, T2D and adiposity, and increased insulin sensitivity.