Background; Overweight and mild obesity are associated with insulin resistance and mild elevations in lipid risk factors which are not usually sufficiently abnormal to merit treatment. Such people are encouraged to lose weight to reduce their risk of progressing to type 2 diabetes and coronary heart disease, but there is clearly a potential role for dietary modifications to maximize any potential benefit of this weight loss. Cocoa flavanols (CF) are known to have vascular effects which might enhance substrate delivery to metabolically active tissues, and thus improve insulin sensitivity.