A high intake of saturated fat is an important risk factor for coronary heart disease (CHD) and type 2 diabetes. However the declining rates of CHD in many affluent societies and the steady increase in type 2 diabetes worldwide suggest that these important causes of serious morbidity and premature mortality have differing risk or protective factors worldwide. Changed macronutrient composition, reduced cigarette smoking, and improved treatment of risk factors and acute cardiac events might explain the reduction in risk of CHD, whereas the increasing rates of obesity are probably the most important explanation for the increase in diabetes. Coronary risk factors associated with diabetes could outweigh improvements in conventional cardiovascular risk factors such that the decline in CHD could be stopped or reversed unless rates of obesity can be reduced. Reduced intake of saturated fatty acids and other lifestyle interventions aimed at lowering rates of obesity are the changes most likely to reduce the epidemic numbers of people with type 2 diabetes and CHD.