The Atkins Diet No-No consists of three items: CARB, BUN, and SUGARS. CARB stands for carbohydrates, which are a type of macronutrient found in many foods that provide energy to the body. BUN stands for buns, which are a type of bread product typically made with wheat flour and yeast. SUGARS stands for SUGARS, which are a type of simple carbohydrate found in many foods and drinks that provide energy to the body. All three of these items are not allowed on the Atkins Diet, as they are high in carbohydrates and can lead to weight gain.