A study published in Economics & Human Biology last month found that as income rises from the lowest to the middle quintile, so does the amount of fast food consumed, and "more work hours predict greater fast-food intake."

The middle class consumes more fast food than the poorest and the wealthiest cross sections of society, according to this study. The idea is the more hours you work, the less leisure time you have and the more likely you are to turn to convenience for eating.

Why it matters: This could affect how we think about food deserts, or low-income areas without access to supermarkets, and how to increase consumption of nutritious food to reduce obesity.

A bigger predictor of whether you are a fast-food eater is nutritional label-use and soda-drinking; those who checked nutrition labels and drank less soda also consumed less fast-food.