Nutrition claims (NCs) on food packaging are, from one side, an informative tool about the nutritional characteristics of the product. From another side, they could bias the consumer in perceiving such products as healthier than those without claims. In order to investigate whether products with NCs have a better nutritional composition that those without claims, the present study aimed to compare the nutrition facts of 376 breakfast cereals, with and without fibre-related NCs, available in 13 Italian retailer online stores. Among these products, 73 items claimed to be a “source of fibre” and 109 “high in fibre”. In addition to a higher fibre content, products “high in fibre” showed higher protein and fat contents but lower carbohydrate, sugar and salt contents compared to both “source of fibre” and without fibre-related NC items. Overall, a high variability in nutritional values was also observed within products with the same type of fibre-related NC. In conclusion, the results suggested that fibre-related NCs should not be considered as a marker of a better nutritional composition of breakfast cereals, and thus consumers should be educated to carefully read the entire nutritional information reported in the food labelling.