While there are many benefits to eating well, the data are mixed on whether diet alone can prevent certain cancers from returning. Nevertheless, there is strong evidence that a plant-based diet cuts the risk of cancer overall. Many epidemiologic studies have shown that people who eat diets rich in fruits and vegetables and sparse in meat and animal fat have lower rates of some cancers, including lung, breast, colon and stomach cancers.

The mechanisms at work are still being explored, but studies indicate that red meat promotes inflammation in human tissue; this inflammation is believed to stimulate the growth of cancerous tumors. Plant foods, on the other hand, contain antioxidants such as beta-carotene, lycopene, and vitamins A, C, and E, which protect the cells from free radicals - unstable molecules that damage healthy cells and are linked to aging and disease.

Phytochemicals, also found in fruits, vegetables, legumes and grains, are compounds that may thwart the action of carcinogens (cancer-causing substances) and aid cells in blocking the development of cancer.

There is evidence that being overweight, which is a risk factor for numerous types of cancer, also increases the chance of recurrence and lowers odds for survival. Research has shown that women who gain more than 13 pounds during treatment for early-stage breast cancer are 1.5 times more likely to experience a cancer recurrence. Studies show that for men who have had prostate cancer, being overweight or obese raises the chances that their cancer will recur, spread, or lead to death.

During cancer treatment, many people lose weight because chemotherapy and radiation side effects, such as nausea, taste changes and loss of appetite, make eating unpalatable; sometimes the therapy itself impairs the absorption of nutrients. Other people may put on pounds from medications, reduced activity, or emotional and stress-related eating. Consulting with a dietician may help you develop the best eating plan for your situation. Ask your doctor for a referral.

Whether you want to gain, lose, or maintain weight, experts recommend that cancer survivors follow these guidelines for a healthy diet:

• Eat a minimum of five servings of fruits and vegetables a day. A serving can be a cup of dark leafy greens or berries, a medium fruit, or a half cup of other colorful choices; use plant-based seasonings like parsley and turmeric;
• Go for whole grains. Opt for high-fiber breads and cereals, including brown rice, barley, bulgur, and oats; avoid refined foods, such as donuts and white bread, and those high in sugar;
• Choose lean protein. Stick to fish, poultry, and tofu, limiting red meat and processed meats;
• Keep dairy low fat. Select skim milk, low-fat yogurt, and reduced-fat cheeses.

Other tips to maximize nutrition:

• Aim for a variety of foods. Create a balanced plate that is one-half cooked or raw vegetables, one-fourth lean protein (chicken, fish, lean meat, or dairy) and one-fourth whole grains;
• Eat fatty fish, such as salmon, sardines, and canned tuna at least twice a week. The fats in these fish are the "good" heart-healthy omega-3 fats; other sources of these fats include walnuts, canola oil, and flaxseeds;
• Limit alcohol consumption. Alcohol has been linked to cancer risk. Men should have no more than two drinks a day; women should have no more than one drink;
• Eat foods high in vitamin D. These include salmon, sardines, fortified orange juice, milk, and fortified cereal. Research suggests that vitamin D, which also comes from sun exposure, prevents cancer and may decrease the risk of recurrence and improve survival. People in regions with limited sunshine may be deficient and thus benefit from a vitamin D3 supplement (ask your physician about a blood test to measure deficiency);
• Food – not supplements – are the best source of vitamins and minerals. There is no evidence that dietary supplements provide the same anti-cancer benefits as fruits and vegetables, and some high-dose supplements may actually increase cancer risk.
• Be "mindful" when eating. Research suggests that we tend to eat more calories and food with fewer nutrients when we are watching TV, driving, or doing other activities.

Research on the nutritional benefits of organic fruits and vegetables has been mixed, and there have been no studies examining whether organic produce is better at preventing cancer or cancer recurrence than non-organic produce.

Stephanie Meyers, a senior clinical nutritionist at the Dana-Farber Cancer Center in Boston, tells her clients to buy whatever produce they like, and to rinse all fruits and vegetables thoroughly with clean water. Buying organic foods is a personal choice, Meyer says, and cancer survivors do themselves no harm by not choosing to go organic.

For more information on pesticides in produce, visit the Environmental Working Group's Shopper's Guide.