This chapter examines the roles of carbohydrates, sugars, starch, and fiber in the body and explains their differing chemical compositions, dietary sources, and metabolisms.  It explains the importance of fiber and resistant starch, particularly for the gastrointestinal system and microbiome (gut health).  The chapter highlights how added sugars increase risks of obesity, diabetes, heart disease, and dental decay and explores whether sugar-sweetened beverages (SSBs), ultra-processed foods (UPFs), and high-fructose corn syrup (HFCS) are to blame.  It emphasizes that all added sugars compromise health, not just HFCS, and most people eat too much.  Sugar-free and low-calorie sweeteners in diet soda and artificial sweeteners like aspartame and saccharin may have long-term metabolic effects, with mixed results on obesity, chronic disease, and cancer.  The chapter closes by considering whether sugar is as addictive as cocaine or opiates, emphasizing moderation in creating healthy diets by decreasing sugar, increasing fiber, and making science-based dietary choices.