Eating for Cancer

Myths, Misunderstandings and Diet Trends

By Amy Bragagnini, MS, RD, CSO

At Trinity Health, our cancer care experts combine the latest research and technology with personalized support inspired by you and your unique journey. From diagnosis to treatment and beyond, we’re here to guide you every step of the way with care that nurtures your body, mind, and spirit.

That includes separating facts and myths about cancer and nutrition. As a Board-Certified Specialist in Oncology Nutrition, I share the following information with my cancer patients on a regular basis.

Sugar and Cancer
Does sugar feed cancer? There is no clear “yes” or “no” answer.

Our body breaks down carbohydrates into blood glucose. Carbohydrates are the body’s preferred fuel source. Glucose provides fuel for all cells in the body (healthy cells and cancer cells), but this does not necessarily mean that glucose is directly responsible for causing cancer cells to grow and spread throughout the body.

Consuming too much sugar is not good for our health. It promotes weight gain and obesity. It also increases a person’s risk for heart disease and diabetes.

From a hormone standpoint, diets that are high in simple sugar increase the production of insulin and insulin-like growth hormones. High levels of insulin and insulin-like growth hormones lead to increased cell growth and division in both healthy and cancer cells.

Balance is the key to consuming sugar and carbohydrates, especially during cancer treatment, but eliminating all sugar could harm some healthy cells. Because malnutrition and weight loss are common during cancer treatment, cancer patients still need carbohydrates.

TIP: To have healthy blood sugar control, eat a diet with healthy fiber (healthy nuts and seeds, whole grains), protein (lean meats, beans, peanut butter, and low-fat dairy products) and healthy fat (avocados and olive oil). Limit foods with added sugar, such as sodas, candy, and desserts. Women should limit their added sugar to 24 grams a day. Men should limit their added sugar to 36 grams a day.

Soy and Breast Cancer
While most normal breast cells have some estrogen receptors, the presence and quantity of these receptors can vary significantly, and some breast cancer cells may not have any estrogen receptors at all, making them "estrogen receptor negative “tumors.” Some breast cancers (estrogen receptor (ER) positive breast cancer) use human estrogen to grow and spread.

The chemical structure of soy isoflavones is somewhat similar to human estrogen, and it can mimic the action of estrogen under certain conditions. So, the question is this: Can the isoflavones of soy stimulate the growth of ER-positive breast tumors?

Contrary to what is thought, isoflavones may reduce breast cancer risk. In fact, soy’s isoflavones may block estrogen from joining with receptors. Studies of healthy women in the U.S. have shown either no association between soy and breast cancer or a protective association against developing cancer.

The American Cancer Society says soy is safe to eat. Sources of soy include soybeans, tempeh, edamame, soy milk, tofu, bean curd, soy nuts, and miso. 

TIP: Current recommendations for consuming soy: about two servings of whole soy foods per day, such as ½ cup of tofu or 1 cup of soy milk. Limit intake of soy supplements as they are not regulated by the Food and Drug Administration and may contain harmful impurities or additives.

Intermittent Fasting
People often fast intermittently to lose weight. One method of intermittent fasting involves not consuming food for specific periods of time, such as following an “eating window” from 8 p.m. to 8 a.m. Another method would be to eat normally for five days a week and consume less than 500 calories for two nonconsecutive days of that week.

There is speculation that fasting may actually help damage cancer cells. There have been clinical trials looking at intermittent fasting and while the subject is undergoing cancer treatment — trials with humans and animals. Some studies have shown that intermittent fasting may enhance the effectiveness of chemotherapy and radiation therapy for patients with certain types of cancer.

Intermittent fasting has potential pros and cons. It may improve insulin sensitivity and the metabolism of fat, help manage hunger, and improve the effectiveness of specific anticancer treatments.

However, because patients undergoing cancer treatment often have side effects that make eating difficult, intermittent fasting could put them at risk for malnutrition. The scheduling of the fasting can also be difficult for people with busy lives. There is also the potential to overcompensate for fasting when the “eating window” opens, leading to consuming too many calories. Intermittent fasting is not recommended for patients on diabetes medication.

Ketogenic Diet
When the body’s glucose/glycogen stores are depleted, the body breaks down fat and produces ketones, which provide energy when glucose is scarce. In some ways, the ketogenic diet mimics fasting by cutting the body’s access to carbohydrates and sugar.

Healthy cells can use ketones for energy. Cancer cells may not be able to get their energy from ketones. Many claims about this diet are drawn from lab and animal studies. It’s important to remember that what happens in an animal is not automatically translated to effects on humans.

The ketogenic diet may:

•    Improve DNA repair in normal cells
•    Improve body weight
•    Enhance the effects of specific cancer treatments

However, a ketogenic diet may produce these side effects in cancer patients:

•    Constipation
•    Lethargy
•    Decreased Appetite
•    Hypoglycemia
•    Headache
•    Weight loss
•    Malnutrition

Given the restrictive nature of this diet, speak with your oncologist or registered dietitian before you begin following the ketogenic diet.

Juicing or “Detox” Diets
Juicing does not detoxify the body. We have organs that do that, such as the liver and kidneys.

Juicing could be a good way to increase the number of fruits and vegetables in a patient’s diet. It also is a source of hydration and a quick way to deliver micronutrients for healthy nutrition.

However, juicing may not be as satisfying as eating whole fruit or vegetables. Juicing may increase blood sugar if a person consumes too much fructose in the juice.

TIP: If you juice, use nutrient dense produce, such as beets, kale, tart cherry, and black currants. Juice more vegetables than fruit and add protein plus a healthy fat. Do your best to keep the fiber in the juice. Do not juice in place of an entire meal, and do not juice for weight loss. Only juice for your health.

Supplements in Cancer Care
Remember: The supplement industry is not regulated by the Food and Drug Administration. However, if a bottle has a USP symbol, it means that the manufacturer has sent the product to a third party to verify it contains what it says it does.

During cancer treatment, the best sources of nutrients are foods and beverages, not supplements. However, sometimes supplements are needed, such as when a patient has a vitamin or mineral deficiency. Also, during certain life stages — such as prenatal and menopausal — supplements may be beneficial.

When it comes to supplements, many people think if “a little is good, then more is better.” I become concerned when patients are mega-dosing vitamins and minerals because there is a chance they may interfere with cancer treatment. Always ask your doctor before taking supplements.

*Reputable sites for information about herbal supplements are the following:

•    NatMed Pro   
•    www.ConsumerLab.com 
•    Memorial Sloan Kettering Cancer Center’s “About Herbs”

The “Health Halo” Effect
This is the perception that a particular food is good for you when there is little or no evidence to support that belief. Consumers need to be aware that the food and beverage industry uses words that may trigger a false perception about a product. It is not that the word itself is inaccurate or untrue, but that it does not provide a full context of the benefits/harms of the product. For example:

•    Fat-free (What about the carbs and added sugars?)
•    Organic (organic macaroni and cheese is still macaroni and cheese)
•    All natural (French fries made with “natural” oil, salt and potatoes)
•    No sugar added (What about carbohydrates, fats, and calories?)

To learn more about our cancer services, visit TrinityHealthMichigan.org/oncology.