A new systematic review and meta-analysis of randomized controlled trials has found that zinc supplementation can improve insulin resistance and reduce inflammation and oxidative stress in people with diabetes and related conditions. Notably, however, zinc did not significantly improve every measure of blood sugar control. Rather than this diminishing the importance of nutrition, the findings instead highlight a fundamental problem with the way nutritional therapies are often investigated: complex chronic diseases such as diabetes are unlikely to be optimally controlled by any single nutrient acting alone.