The risk of specific cancers increases in patients with metabolic dysfunction, including obesity and diabetes. Here, we use Drosophila as a model to explore the effects of diet on tumor progression. Feeding Drosophila a diet high in carbohydrates was previously demonstrated to direct metabolic dysfunction, including hyperglycemia, hyperinsulinemia, and insulin resistance. We demonstrate that high dietary sugar also converts Ras/Src-transformed tissue from localized growths to aggressive tumors with emergent metastases. Whereas most tissues displayed insulin resistance, Ras/Src tumors retained insulin pathway sensitivity, increased the ability to import glucose, and resisted apoptosis. High dietary sugar increased canonical Wingless/Wnt pathway activity, which upregulated insulin receptor gene expression to promote insulin sensitivity. The result is a feed-forward circuit that amplified diet-mediated malignant phenotypes within Ras/Src-transformed tumors. By targeting multiple steps in this circuit with rationally applied drug combinations, we demonstrate the potential of combinatorial drug intervention to treat diet-enhanced malignant tumors.