Results of an early study suggest that dairy-free diets and unconventional food preferences could put boys with autism and autism spectrum disorder (ASD) at higher than normal risk for thinner, less dense bones when compared to a group of boys the same age who do not have autism. The researchers believe that boys with autism and ASD are at risk for poor bone development for a number of reasons. These factors are lack of exercise, a reluctance to eat a varied diet, lack of vitamin D, digestive problems, and diets that exclude casein, a protein found in milk and milk products.