Developmental plasticity enables an intestinal tapeworm to adapt to dietary stress

Diet is one of the strongest ecological forces shaping the gut environment, yet its impact on intestinal worms, termed helminths, remains poorly understood. The helminth Hymenolepis diminuta provides a powerful model for exploring how lifestyle shifts in modern societies may disrupt host-helminth relationships. Here we show that dietary fiber availability influences the developmental trajectory of H. diminuta. Using Wistar rats fed a Western-type low-fiber diet, we demonstrate that fiber depletion halts helminth growth and reproduction, with gene expression changes consistent with suppressed development and altered metabolism in contrast to a fiber-rich diet. These effects coincide with diet-dependent shifts in the host gut microbiota and metabolic environment, with fiber-rich diets supporting communities linked to intestinal homeostasis and the Western diet favoring inflammatory profiles. Together, these findings suggest that dietary transitions in industrialized societies may contribute to the decline of helminths and influence the efficacy of helminth-based therapies.