This study will investigate whether the lacto-tripeptide Ile-Pro-Pro (IPP) improves the function of the endothelium in patients with coronary artery disease. The study has a crossover design. Participants will be treated with a protein hydrolysate rich in IPP for 12 weeks and placebo for 12 weeks with a four-week rest period between treatment periods. The investigators will use ultrasound to test the function of the endothelium in the brachial artery before, after 6 weeks, and after 12 weeks of each treatment. Blood will be collected before and after each treatment. The investigators hypothesize that IPP will improve endothelial function.