The quality of food determines life expectancy. However, the quality of food can as well be a savior as a menace. This is best understood in the contribution of food to the rise, and the subsequent standstill, of life expectancy during the past century and a half.
Average life expectancy almost doubled. This great achievement I have always attributed to the presence of clean water and better health care. This is only true to some extent. The rise in life expectancy must be mainly attributed to the mechanization of food production in the US.