Food quantity is not food quality: as resource supply increases, producers can become more abundant but poorer in essential nutrients, which can limit the growth of the consumers that depend on them. This talk presents stoichiometric ordinary differential equation models of producer–consumer systems (such as algae and zooplankton) in which a consumer’s feeding effort, which raises intake but carries an energetic cost, is a trait that evolves along its fitness gradient. We analyze the models using positive-invariance and boundedness results, boundary-equilibrium stability, numerical simulation, and bifurcation analysis across resource levels. For a single consumer, adaptive feeding effort can rescue a population under severe nutrient limitation, but fast adaptation widens the population cycles, raising the risk of stochastic extinction. We then extend the model to two consumers competing for one producer and allow only the weaker competitor’s feeding effort to adapt. Adaptation expands the conditions under which the weaker competitor persists, allows both consumers to persist over a narrow range of resource levels, and can reverse which species dominates. These benefits are conditional: they disappear when nutrient loading makes the producer too poor in nutrients, and when adaptation is too slow relative to the ecological dynamics. Together, the results show how coupling nutrient constraints with trait dynamics can change the stability and long-term behavior of ecological systems.