Know what foods cancer patients must avoid. A doctor-approved guide to help reduce inflammation, boost immunity & support treatment. Diet plays a major role during cancer treatment. Some foods can worsen inflammation, reduce immunity, or interfere with treatment response. Here are the key items cancer patients must avoid: 1. Deep-Fried & Oily Foods Fried foods contain unhealthy fats that cause inflammation and slow digestion. They may also worsen nausea during chemotherapy or