Nowadays, many people struggle with various diseases, and to prevent this, a low-carbohydrate diet is recommended. Consumers are also looking for products with a high amount of plant proteins. This study investigated the preparation of low-carbohydrate and high-protein breads using flaxseed flour, buckwheat flour, and pea protein enriched with watermelon seed flour at different contents (0, 5, ... [Show full abstract] 10, and 15%). The physical, chemical, and sensory properties of the bread were determined. Based on the research conducted, the loaves of bread with the addition of WSF had a higher volume compared to the control sample, but in the case of parameters of crumb color, no significant changes were observed (∆E < 5). Taking into account the sensory analysis, it is recommended to add 5% WSF to the base recipe; such bread meets the requirements for low-carbohydrate and high-protein food. The value of the amino acids (mg/g−1) in the obtained bread was in the order of glutamic acid (64.9), followed by asparagine (37.3), arginine (32.6), lysine (20.4), serine (18.0), and alanine (17.0),higher than the corresponding value in the control bread. The findings suggested that the addition of WSF at a concentration of 5% could be used as a valuable functional ingredient to enhance the nutritive content of low-carbohydrate and high-protein bread, especially for the elderly and physically active people.