Here's a great study! A study published in the Lancet (link below) estimated the impact poor diet has on the risk of death from heart disease, diabetes and certain cancers. Poor diet and malnutrition is the leading risk factor for death -- larger than tobacco use and high blood pressure.
Malnutrition comes in two forms: eating too much (obesity) and not eating enough (hunger). Annually, malnutrition worldwide costs an estimated $3.5 Trillion (with a T!) in healthcare costs! Which countries ranked best? Israel, France, Spain and Japan who all have a diet similar to the Mediterranean diet consisting of higher amounts of fruits, veggies, nuts, olive oil and omega 3s from fish.