Diet-induced thermogenesis (DIT) is a concept that has been well known in one form or another for more than a century in vertebrate nutrition and physiological ecology. Yet, it is practically unknown in the physiology and nutritional ecology of insects. We suggest that DIT is a ubiquitous mechanism occurring in most if not all organisms and functions to maintain nutritional homeostasis by metabolically oxidizing excess energy intake to maintain a metabolic pool of nutrients that is balanced in both energy and nutrients. There is sufficient evidence to suggest the phenomenon exits in insects and should be considered as a viable hypothesis to enrich the paradigms of insect nutritional ecology and biological stoichiometry. We demonstrate evidence for DIT in the phytophagous spruce budworm (Choristoneura fumiferana [Clemens]). Budworm larvae with the highest dietary metabolizable energy/protein ratio and highest assimilated food are the least metabolically efficient and are apparently able to oxidize excess metabolizable energy intake (i.e., they exhibit diet-induced thermogenesis). Metabolic adaptations such as DIT would allow organisms to use foodstuffs that are high in energy but critically low or unbalanced in essential nutrients to maintain normal growth, survival, and reproduction. Understanding the role DIT plays in nutritional and elemental stoichiometric homeostasis of insects may be an important element in interpreting their nutritional ecology.