For more than 3 decades, colorectal cancer (CRC) incidence rates have been increasing rapidly among adults <50 years of age (ie, early-onset CRC) in the United States and in other parts of the world.1 More recently, incidence rates have started to increase in adults ages 50–54 years old.2 Despite broad recognition in the medical and public health communities about the increasing morbidity and mortality associated with early-onset CRC, the factors driving this increase are largely unknown. Many studies have investigated risk of early-onset CRC associated with traditional, well-known risk factors for CRC , including a Western diet,3 heavy alcohol use,4 tobacco use,5 sedentary behavior,6 obesity,7,8 and diabetes.