Story at-a-glance A high-fat diet makes it easier for breast cancer to spread by activating clotting cells, increasing inflammation and altering blood vessels in ways that help tumors grow Mice on high-fat diets had nearly five times more cancer cells in their lungs, even when their tumors were the same size as leaner mice A high-fat diet increased fibronectin, which acts as "molecular glue" helping cancer cells attach to blood vessels, while obesity increases inflammatory compounds that worsen this buildup Switching to a normal-fat diet for just seven days significantly reduced clotting activity, fibronectin buildup and the number of cancer cells lodging in the lungs Eliminating vegetable oils and reducing total fat intake to 30% to 40% of daily calories lowers inflammation and reduces your risk of cancer spread