Questions and Answers about Nutrition and Cancer (The James)

Questions and Answers about Nutrition and Cancer

What should I know about dietary/herbal/nutrition supplements?

Many dietary, herbal and nutrition supplements may be dangerous if used during your cancer treatment. A supplement or product that is labeled as "natural" does not mean it is safe to use. Supplements may interact with other medicines you take and can cause health problems such as bleeding, changes in your blood pressure or organ damage. Many supplements have not been tested in clinical studies and the effects they may cause are not known. Dietary, herbal and nutrition supplements are not controlled like prescription medicines. Some products made outside of the United States have been found to contain harmful substances. It is important to talk with your health care team about any supplements you take and to learn how they may affect your cancer treatment.

Will caffeine increase my risk of cancer?

Caffeine may be found in coffee, teas, soda, energy drinks, chocolate and some medicines. For most people, caffeine does not increase their risk of cancer. Some research has found that caffeine may help decrease the risk of cancer. Coffee and tea contain nutrients, called antioxidants that help your body repair damage to its cells. For most people, it is safe to drink up to 400 mg of caffeine each day. The amount of caffeine in drinks may vary. Look at the food label to find out how much caffeine is in your drink.

ProductAmount of Caffeine

Coffee (8 ounce)

100 to 200 mg

Hot Tea (8 ounce)

15 to 60 mg

Energy drink (8 ounce)

50 to 150 mg

Soda Pop (12 ounce)

35 to 55 mg

If you have health problems including heart problems, high blood pressure, heartburn, indigestion, diarrhea or constipation, it may be best to limit the amount of caffeine in your diet. Talk with your doctor or dietitian about the amount of caffeine that is safe for you.

Is there a link between sugar and cancer?

There is no research that shows a direct link between a high-sugar diet and cancer. However, a diet high in sugar-sweetened foods and drinks can lead to excess weight and body fat, which may increase your cancer risk.

What is a Ketogenic (Keto) Diet?

The keto diet is a very strict low-carbohydrate (carb) diet that includes eating mostly high fat and high protein foods. This diet may cause quick weight loss in most people, but it is not a healthy way to lose weight. The keto diet is hard to maintain over time because it is so strict. People often gain back some or all of the weight lost after they stop the diet. There is no single food or diet that can cure cancer. It is important to talk with your doctor or dietitian about what diet is best for you. Until more research is done, the keto diet is not recommended for most cancer patients.

Can I eat and drink dairy products?

Dairy products have important nutrients that help to lower your cancer risk. It is important to make sure any dairy products you eat or drink are pasteurized. Dairy products that have been treated with hormones will not affect your hormone levels and do not cause any added risk for cancer patients.

Does Genetically Modified Organisms (GMO) cause cancer?

Genetically modified foods are produced from plants or animals that have had specific changes made to their DNA by a process called genetic engineering. For example, this process can help make plants stronger to survive during cold weather or a drought. There is not enough information to determine if GMOs increase your cancer risk.

Can eating organic food lower cancer risk?

Organic food is grown without the use of man-made fertilizers, pesticides and products that control insects, bacteria and weeds. Organic farmers may use organic pesticides to control pests and weeds. For a food to be certified organic, at least 95% of the food must be made up of organic ingredients.

There are many reasons why people choose to buy organic food, such as a concern for the environment or animal welfare. People may also choose to buy organic food because they feel it is safer and more nutritious than other food and does not use man-made fertilizers and pesticides that may increase the risk of some diseases.

There is little research to show that organic foods may offer more protection from cancer. Studies have found that you can lower your cancer risk, if you do not smoke, stay active and eat a healthy diet that includes fruits, vegetables, whole-grains and plant-based proteins.

Is it okay for me to eat foods with soy and ground flax?

Foods with whole soy and ground flax are safe when eaten as part of your regular diet. It is important to talk with your doctor, pharmacist or dietitian to learn more about what foods are safe to eat.

Until more is known about the effects of soy and flax on cancer, we recommend that you do not take them in supplement form, such as pills or powders. Instead, eat whole soy foods, such as edamame, tofu, roasted soy beans or soy milk. Avoid processed foods that have concentrated forms of soy or flax. To tell if a processed food has concentrated amounts of soy or flax, look at the label. Soy or flax will be listed as one of the first 3 ingredients on the label. Concentrated amounts of soy may be found in protein powder, granola bars, health shakes and high-protein cereal. Concentrated soy may be listed on the food label as:

  • Soy protein isolate
  • Isolated soy protein
  • Concentrated soy protein

Soy sauce, soybean oil and soy lecithin are okay to use. These products do not have phytoestrogens and do not cause any added risk for cancer patients.


© April 19, 2019. The Ohio State University Comprehensive Cancer Center – Arthur G. James Cancer Hospital and Richard J. Solove Research Institute.

This handout is for informational purposes only. Talk with your doctor or health care team if you have any questions about your care.

For more health information, call the Patient and Family Resource Center at 614-366-0602 or visit