**3. Immune-Unhealthy Diet Model (IUNHDM)**

A Global Nutrition report (2016) stated that every third person in the world is inflicted with malnutrition [32]. On this basis, a pre-clinical experiment proved that high protein and fructose diets damage the immune system and cause cancer [33–35]. In this section, we highlight why a weak immune system fails to protect the human body from developing cancer; we do this using a similar system to that presented in (1) and under the assumption that the person follows an unhealthy diet. For instance, the western-style diet which is characterized by a high consumption of proteins (especially high in processed and red meats), sugar, salt, and fat when compared to a healthy diet comprising an intake of fruits and vegetables [36–38]. Several studies showed that a high sugar and protein diet damages the immune system and promotes cancer [33,34,39]. Hence, In the IUNHD, the effects of an unhealthy diet are presented dynamically according to the rate of two parameters: *μ* and *η*. In this section, we analyze the model considering an example where the immune system is weak as a result of the person following an unhealthy diet.
