Background: nutrition therapy is a complex area of healthcare systems that encompasses patient characteristics, medical decision making, nutritional formula characteristics, and costs, composing a complex ecosystem. The integration of these different domains is actualized in medical prescription in a heuristic and iterative way, taking into account patient characteristics and formulas, with a limited capacity for in-scale calculations and inclusion of factors involved in the prescription of nutritional formulas and other ecosystem elements. From a practical standpoint, depicting the four areas as equalities could provide the necessary equivalence to study dependence and consequence from left- and right-side terms. Objectives: the objective of this theoretical study is to provide a mathematical model that describes and integrates different aspects of nutrition therapy. Methods: in this theoretical study, we deducted a mathematical representation for nutrition therapy using first-grade equations and simple calculus techniques. Results: a formula that coordinates four elements of the nutrition therapy ecosystem was found: cashflow, compliance adherence, patient, and macronutrient mass, formula density and unitary cost. Conclusion: factors involving decision-making in nutrition therapy can be unified in a mathematical model.