Debunking Diet and Cancer Myths in the Clinic

This transcript has been edited for clarity.

Hi. My name is Dr Shikha Jain. I am a gastrointestinal medical oncologist at the University of Illinois Cancer Center, and also the founder of the nonprofit Women in Medicine. I’m here to talk to you today about some of the myths that we hear around food and diet and how it can impact cancer.

One of the most common myths that I hear in my clinic all the time is that sugar feeds cancer, and I can tell you that that is categorically not true. One of the reasons people sometimes think that is because a scan called a PET scan does capture cells that are rapidly replicating, and those rapidly replicating cells ingest sugar. Oftentimes, people think that because the PET scan is lighting up where those cells are rapidly replicating, the cancer is actually eating sugar.

That is not the way it works. I have patients who’ve tried to cut sugar completely out of their diets thinking it’s going to help them, and in actuality, it doesn’t help. In some situations, especially when you’re having nausea or feeling uncomfortable or having a stomach upset, sometimes sugar can make you feel better if that is what you’re craving at the time and you’re not really craving other foods.

I strongly recommend you eat a healthy diet. You don’t need to overdose on the sugar, and especially if you have diabetes, make sure you’re managing your sugar. Sugar does not feed cancer, so please do not cut sugar completely out of your diet because it won’t help you treat cancer, nor will it help you prevent cancer.

Another very common myth that I hear is talking about things like superfoods or things that might prevent cancer because they are considered to be antioxidants and kill off cancer cells. We know as oncologists that there are many different types of foods that can actually cause cancer. For example, if you eat a diet high in processed meats or high in red meat or processed foods in general, if you’re eating some of the candies, and some of the things that people use to quit smoking have nicotine and things in them.

We know smoking is very bad for cancer. Alcohol in excess can be very damaging to the liver and the pancreas and can also cause kidney cancer or bladder cancer. Those are all things from your diet that you can remove or avoid to help you stay healthy and prevent diagnosis of cancer.

For things like vitamin supplements — I hear often about vitamin C and about turmeric and other types of foods that might help prevent cancer — there are no data currently that show any of those foods prevent cancer. There is some evidence that turmeric can be an anti-inflammatory, so some people do take turmeric in small doses or in their food as an anti-inflammatory agent, and there’s nothing wrong with that. Again, you don’t want to take too much because too much of anything can be dangerous.

People also ask me about green tea because green teas are seen as a very healthy option for you to be drinking. Green tea can be healthy, and it can be good. It can be a good thing for you to drink occasionally, but what people don’t understand or know is that too much green tea can thin your blood and put you at a higher risk for bleeding.

Any sort of thing that you’re ingesting, make sure that you talk to your doctor so they understand exactly what you’re taking, and if there’s any possibility that it might cause any complications that you may not be aware of.

The other thing I tell all of my patients is that I believe in holistic care. I believe in healthy eating. I believe in diet and exercise as ways to stay healthy. I also believe that you need to make sure that you talk to your care team about what vitamins, what supplements, what you’re putting into your body. Because what some people don’t realize, especially if you’re on any chemotherapy or systemic therapies, some of the supplements that you might take might interact with some of the systemic therapies.

For example, if you’re on a chemotherapy agent and the supplement that you’re taking actually blocks absorption of that chemotherapy agent, it may not be as effective, or it could make it more toxic. You have to be careful that whatever you’re taking, you talk to your doctor and the pharmacy team to make sure that it’s not interacting in a negative way with the medications that you’re taking as prescribed for your cancer.

I think many people don’t realize how much exercise can impact and positively impact your life if you’re going through a cancer diagnosis. We know that exercise helps prevent heart disease and helps keep us healthy overall, but there’s studies that have shown that exercise during and after receiving treatment for your cancer can prolong your life almost as much as some standard therapies.

If your patient is taking standard therapy and feeling a little sluggish, that is completely understandable, but adding exercise into their diet can be a really impactful way to keep healthy and stay alive longer. There are many different ways to take supplements, take holistic care, and take good care of oneself.

Just make sure you’re talking about what is safe and what is not. You would not believe how many patients come to me with supplements or over-the-counter vitamins. I share stories with them of patients who took some of these supplements and, because they aren’t regulated by the FDA, some of those patients actually ended up in liver failure.

I had a patient when I was in training who took a supplement as it was “prescribed” or as it was listed on the bottle. She ended up needing a liver transplant with no other medical problems, and she was very young. Again, many of these supplements can be dangerous if they’re not taken properly and if they’re not monitored by a doctor.

The final thing I want to say that I think is so important is that doctors and patients are a team. We don’t know what happens when the patient goes home at the end of the day. We can give recommendations based on evidence and science, and our goal is to help keep you healthy, stay healthy, and stay alive as long as possible. In order to do that, we need to have an open and honest discussion, there needs to be shared decision-making, and we need to make sure the decisions being made are informed and are based on good science and evidence.

Be careful when there is a celebrity or somebody online trying to sell you a supplement, because oftentimes they have a secondary gain. They might be making money from the supplement, or they might have a brand deal with them. Patients need to be really cautious when people who aren’t their doctor are telling them different supplements and holistic things to take, because they may be selling these things for some secondary gain for themselves that doesn’t actually benefit the patient. It doesn’t mean that they’re bad people. It doesn’t mean that they’re malicious people. What it means is they have a reason for what they’re trying to sell, and your patients just need to make sure that they're thinking very carefully about what goes into their bodies.

Those are very common sources of myths about diet and exercise. I hope that you have a good doctor-patient relationship and are able to talk about these things; come up with exceptional science- and evidence-based, holistic ways to manage medical care; and find great ways to have a partnership with your care team so that the patient feels comfortable with the outcomes.

A version of this article first appeared on Medscape.com.