American diet/activity patterns were estimated to account for 309,000 to 582,000 deaths -- out of a total of 2,148,000 -- in 1990 See: McGinnis JM, Foege WH. Actual causes of death in the United States. JAMA 1993 Nov 10;270(18):2207-2212.
Diseases of deficiency or excess occur. Here are some examples.
Diabetes, certain cancers (e.g., prostate, colon), cardiovascular disease and hypertension are common conditions with dietary risk factors.