This paper analyzes the role of cereal products in the diet of individuals with disorders of carbohydrate metabolism, with particular emphasis on their impact on postprandial glycemia and the risk of developing type 2 diabetes (T2D). Cereal products, as the main source of dietary carbohydrates, also provide dietary fiber, minerals, B vitamins, and key bioactive compounds such as β-glucans, arabinoxylans, resistant starch (RS), and polyphenols. These components may reduce the rate of starch digestion and glucose absorption in the small intestine by increasing the viscosity of intestinal contents or by directly inhibiting digestive enzymes such as α-glucosidase. It has been shown that fermentation of these compounds by the gut microbiota leads to the production of short-chain fatty acids (SCFAs), which improve insulin sensitivity and stimulate the secretion of incretin hormones such as GLP-1. A literature review confirms that regular consumption of whole-grain products is associated with a reduced risk of T2D, whereas refining processes and excessive grain fragmentation lead to an increased glycemic index of products. Based on clinical guidelines and a narrative synthesis of the available literature, minimally processed whole-grain products were identified as a fundamental component of dietary therapy for diabetes, which is illustrated by the cereal product pyramid presented in the paper. This review involved a comprehensive literature search in PubMed, Scopus, and Web of Science using relevant keywords. Peer-reviewed articles, reviews, and meta-analyses (mainly 2000–2025) were included based on their relevance.