Fibers and proteins act as the most important compounds in reducing appetite and inducing satiety. Satiety can be stimulated much more effectively by consuming a combination of fibers and proteins. Therefore, modifying the formulation of snack products to increase fiber and protein is a good strategy to control appetite and prevent overconsumption. Herein, the proteins used for formulation included calcium caseinate, whey protein, and albumin. Fibers also included inulin, oligofructose, glucomannan, and apple fiber. A D-optimal design was used to optimize fiber and protein-rich snacks by evaluating texture and sensory parameters in the current study. Model selection was based on the significance of the model (p < 0.05) and components (p < 0.1) and non-significance of the lack of fit (p > 0.05). Then, rheological properties were investigated for different formulations in vitro gastric digestion. Also, the microstructure and protein digestion status of the optimized product were assessed. A combination of 30% of protein and 10% of fiber was selected as the optimized sample based on evaluation of textural and sensory characteristics. Proteins played an important role in increasing springiness, cohesiveness, and fibers and increased hardness, resilience, and chewiness by increasing water absorption. Mixing of fibers and proteins prolonged protein digestion during in vitro gastric digestion and reduced the effect of gastric enzymes on the product. In general, a combination of fiber and protein can increase gastric viscosity, delay gastric emptying, and cause a sense of satiety in a person for a longer time.