Cereal grains have always had an important role as staple foods in our diet. They not only provide nutrients, but also other phytochemicals, whose functionalities in food and animal systems are a subject of intensive investigation. Digestible starches have physicochemical properties that can provide desired functionality in food formulations. Indigestible carbohydrates have sparked interest not only as functional ingredients, but also as avenues to reduce calorie intake and to increase the dietary fibre content of foods. Proteins and lipids are the second and third major nutrients, respectively, in cereal grains and their interactions with the dominant carbohydrate fraction can affect the digestibility of starch grain products. Non-carbohydrate phytochemicals include phenolic compounds, which are widely distributed in the plant kingdom with several classes appearing in cereal grains. Some phenolic compounds are endogenous components of the cell wall material. Processed products from whole grains or from milled fractions present an opportunity for scientific investigations that could lead to an understanding of the mechanisms involved when our microbiome interacts with the digestive products of various grain matrices after their delivery from the upper gut. This interaction of cereal-based grain foods with the microbiome is a new area of investigation that is expected to grow with the passage of time.