This work is considering three significant factors that affect blood glucose level: food intake, hereditary predisposition and stress. Goal of this paper is to observe blood sugar level in human organism as a dynamic MISO (Multi Input, Single Output) system, and to describe it with differential equations and control system blocks. The system has three inputs; food (carbohydrates), hereditary factor and stress, and a single output--blood glucose level. Basically, several logical assumptions have been made, as the result of few medical researches. A model that gives outputs, very similar to real ones (measurements of glucose level in human body) is used for more detailed analysis. This model is very suitable for computer simulations and it can easily be tested for different input arrangements. Using this property of the system, several modes of food consumption have been proposed, in order to retain blood sugar level inside recommended limits.