Cereal, as a general food category, is commonly used to support weight gain due to its macronutrient content, particularly carbohydrates and sometimes added sugars or fats. The scientific basis for this use lies in the fundamental principles of energy balance: to gain weight, energy intake must exceed energy expenditure. Cereals, especially those made from refined grains and/or containing added sugars (such as many breakfast cereals), are energy-dense and provide a quick source of calories. Several clinical and observational studies indicate that diets high in refined grains and processed cereals are associated with increased caloric intake and, in some cases, weight gain. For example, research published in nutrition and epidemiology journals has found that higher consumption of energy-dense, processed cereals can contribute to positive energy balance and increased body mass index (BMI) in both children and adults.

However, it is important to note that not all cereals are equally effective for weight gain. Whole grain cereals, which are higher in fiber and have a lower glycemic index, may not promote weight gain as rapidly as their refined counterparts due to increased satiety and slower digestion. The evidence supporting cereal use for intentional weight gain is indirect, as most studies focus on weight gain as an unintended side effect of high cereal consumption rather than as a targeted therapeutic intervention. Nonetheless, the scientific rationale for the use of cereal to support weight gain is well-established through its calorie content and role in energy balance, justifying a moderate evidence rating.