One of the main reasons that the American diet is unbalanced is

It is unbalanced because we(Americans) eat too many calories.  

Explanation:

About 25 years ago, the average american eats about 1,850 calories a day. Our diet as grown about 304. About 68% of Americans are overweight/obese.  The reason for those calories are fatty foods and soft drink. Fast food is part of the American diet. The government recommends that we have at least two to five cups of fruits and vegetables a day. But Americans eats only three servings a day, and 42 percent eat fewer than two servings a day.

your body is trying to warm itself up. or more precisely, sensors in your skin send messages to your brain to generate heat to your body.

your answer would be a, maximum exploitation of resources.