To ensure success in reproduction, organisms dedicate substantial resources to supporting the germline. In testes, somatic gonadal cells form a barrier that isolates germ cells from circulating nutrients, raising the question of how germ cell metabolism is sustained and how somatic cells ensure sufficient resources are directed to the germline. We use lineage-specific manipulations and metabolite reporters to show in vivo that somatic gonadal cells break down circulating sugars to produce and shuttle lactate to the germline, sustaining germ cell survival. We show that somatic cells ensure that carbohydrate metabolism is allocated specifically to germ cell support and that increasing autonomous consumption of carbohydrates in the soma increases germ cell death. Thus, germ cell survival depends on correct metabolic compartmentalisation within gonadal somatic support cells.