The thesis studies determinants and adjustment paths of the people's weight from the view point of rational behavior.It followes the research approach of Becker and Murphy (1988), makes use of the utility function from Levy (2002), and corporates a budget constraint so as to establish an optimal control model for food consumption and weight, and to find out the relationship between them. Negative correlations are found between the steady-state weight and food prices, basal metabolic rate, and time discount rate.Positive correlations are found between the steady-state weight and income, marginal utility of food, and desirable weight. There is a tendancy to guide the actual steady-state weight to a much higher fluctuation margin than that of the desirable weight.In the dynamic analysis, it is also found that, regardless of an increase or decrease of the steady-state weight, both directions of adjustment show that the process of food consumption is always ``overshooting."In other words, when the steady-state weight becomes heavier (lighter), consumers first increase (decrease) their food consumption substantially. And, as the time goes by, there is a gradual decrease (increase) in food consumption owing to the fact that the food consumption is still higher (lower) than what is required for metabolism of the body that makes the weight getting to increase (decrease) till the new equilibrium is arrived.