Lactate, Carbohydrate Restriction and Cancer Metabolism.

Carbohydrate restriction has been proposed as an adjunctive strategy in cancer, largely because many tumours show high glucose uptake. Clinical evidence for benefit remains limited, mixed and often overstated. Lactate is now recognised as more than a metabolic by-product: it influences redox balance, tumour-stromal signalling, immune suppression, angiogenesis, epigenetic regulation and metastatic behaviour. This Review considers carbohydrate-restrictive diets from a lactate-centred perspective. The stronger mechanistic argument is not simple glucose deprivation, but the possibility that lower carbohydrate availability may reduce glucose-to-lactate flux and disrupt lactate-dependent tumour ecosystems in selected contexts. It discusses where this idea is biologically plausible, where claims run beyond the data, and how dietary approaches compare with direct lactate-targeted strategies. To ground the clinical discussion, registered interventional trials of caloric and/or carbohydrate manipulation in cancer were reviewed; they show an active but early-stage field dominated by small, heterogeneous studies and few direct lactate-related endpoints. Future trials should use biomarker-guided tumour selection, direct measures of tumour lactate flux, immune and microenvironmental endpoints, and explicit safeguards for weight, muscle mass, treatment tolerance and quality of life. At present, carbohydrate restriction should remain investigational and be tested only in well-designed clinical studies with clear nutritional safeguards.