Metabolic behaviors of proliferating cells are often explained as a consequence of rational optimization of cellular growth rate, whereas microeconomics formulates consumption behaviors as optimization problems. Here, we pushed beyond the analogy to map metabolism precisely onto the theory of consumer choice and derived a universal linear relationship between the metabolic responses against nutrient conditions and metabolic inhibition. The relationship holds in arbitrary metabolic systems as long as the law of mass conservation stands. It offers quantitative predictions without prior knowledge of systems. As an example, we revealed the correspondence between the Warburg effect, a seemingly wasteful but ubiquitous strategy where cells favor aerobic glycolysis over more energetically efficient oxidative phosphorylation, and Giffen behavior, the unexpected consumer behavior where good is demanded more as its price rises. This highlights that the application of microeconomics to metabolism can offer new predictions and paradigms for both biology and economics.