Dietary restriction (DR) refers to a broad set of interventions that limit the intake of specific nutrients or overall food consumption, either in quantity or timing, without causing malnutrition. DR has long been considered the most robust intervention for increasing healthspan and lifespan. This includes, not exhaustively, caloric restriction (CR), protein restriction (PR), amino acid restriction (AAR), intermittent fasting (IF), and time-restricted fasting (TRF), each with overlapping but distinct metabolic and physiological effects. This brief review examines the current scientific understanding of how some of the most commonly employed DR regimens may impact metabolism, lifespan, and healthspan. Particular attention is given to the underlying biological mechanisms and supporting evidence derived from both human clinical studies and fundamental biological research conducted with model organisms ranging from yeast to non-human primates.