There are too many deficiencies in the studies in terms of diet biscuit in the literature. This study aims to fill this gap in the literature. The % moisture content, structural content verification, thermal stability, degradation properties and % ash content of diet biscuit samples, structural characterizations, surface micromorphology and detailed structural analysis were determined with fast, precise, new instrumental techniques. Thermal degradation of the lemon-fiber diet biscuit sample started at 250 °C in four stages and completed at 585 °C. There is three-stage thermal degradation in wholemeal diet biscuit samples, starting at 229 °C and completed at 580 °C. There are 46.06% C, 1.60% N, 0.12% S and 6.68% H in lemon-fiber diet biscuits, and 45.51% C, 2.39% N, 0.15% S and 7.05% H in whole-wheat diet biscuits. Ca, K, Mg, Na, Zn element contents in diet biscuit samples were determined by AAS technique. In the diet biscuit samples, K was determined as the element with the highest amount and the element with the least amount was Zn. As a result, the work is comprehensive and original. It is believed that the study will fill an important gap in the literature and will be a useful resource for researchers.