Carbohydrates often make up the majority (by weight and % kcal) of custom research diets, with the exception of higher fat diets. Commonly used carbohydrate sources include sucrose, cornstarch and maltodextrin. Other sources include fructose, dextrose (glucose), dextrin, and lactose. Maltodextrin is enzymatically derived from cornstarch to have shorter glucose polymers and is helpful in pelleting high fat diets and in diets where cornstarch exceeds sucrose.

Sucrose is a part of most formulas, often making up 10% of the diet or more. This likely adds to the palatability of the diet. The carbohydrate profile of a diet can be manipulated, although some mixtures may not pellet. There are also diets with very little carbohydrate, thus containing high amounts of fat and/or protein.

Cellulose (fiber) is part of many formulas and while not required by rodents, is considered beneficial. It can also be used to make formulas with differing macronutrient profiles isocaloric.