Buckwheat breads enriched with seeds (e.g., poppy, carum, amaranth, sunflower, and pumpkin) and nuts can be excellent sources of selected macro- and microelements and bioactive components, such as phenolics, essential oils, unsaturated fatty acids, fiber, and vitamins; however, no studies described their impacts on body biochemical parameters and antioxidant status. The aim of this study was to a determine the safety (the analyses of blood morphological and biochemical parameters) of short-term diets based on buckwheat breads supplemented with the commonly used functional ingredients. Additionally, we confirmed the usefulness of these fortified breads in a reduction of blood cholesterol and triacylglycerols, as well as an improvement of in vivo antioxidant status of Wistar rats. Enriched breads presented an increased phenolic content; however, it has not been translated into an elevation of antioxidant capacities. During short-term in vivo experiments, the studied breads increased the body mass of the rats, except the control buckwheat bread. Compared to the control, the poppy-milk bread markedly lowered (–23%) and egg yolk–carum bread significantly increased (+17%) the total cholesterol concentration in serum. All the fortified breads decreased triacylglycerols’ levels by about 50%. Bread enriched with the poppy–milk, milk-seed, egg yolk–carum, and a mix of additives decreased superoxide dismutase activity by 68%, 66%, 73%, and 71%, respectively. Catalase activity was significantly decreased in the rats fed with carum bread (–62%) and markedly increased in the groups fed with egg yolk–carum bread (+89%), hazel nuts–amaranth bread (+72%), and milk–seeds bread (+65%). The results confirmed the usefulness and safety of functional additives in buckwheat breads.