Both undernutrition AND overnutrition can lead to health problems that are burden on the health system. One does not negate the other since both problems can occur simultaneously within a country.

I really doubt that in general the rising costs of health care are from people not getting enough nourishment. I think you’ll find quite the opposite. Obesity and smoking are an almost guaranteed path to chronic illness. Illness such as diabetes, heart disease, and cancer are very expensive to treat.