An October 2006 study in the American Journal of Clinical Nutrition examined the association between eating certain food groups and waist circumference. The study, which lasted five years, followed 22,570 Danish women and 20,126 Danish men.
Waists grew when subjects ate carbohydrates from refined grains, potatoes, and simple sugars. Total protein intake, however, especially animal protein, was inversely related to expanding waist circumference; the more meat you ate, the less your waist grew. Unlike any other carb subgroup, fruit and vegetable intake also caused waist shrinkage. Eating vegetable fats, however, caused waist expansion.