Is there a perfect diet that can reduce your risk for cancer? Our clinical nutritionists weigh in.

Published: August 13, 2019 | Updated: March 23, 2023

There’s a lot of information floating around about food and nutrition and how these contribute to your risk for disease, including cancer. Sorting through the news and research, some of it conflicting, can be confusing and overwhelming.

So, I turned to experts who work in the field every day.

Registered dietitians Jaclyn Moore, Ali Sells and Anita McLaughlin, all clinical nutritionists with Norton Cancer Institute, clear up some of the confusion and break down what’s important to know about how diet affects our risk for cancer.

In what ways is diet important to preventing cancer?

Ali: Scientists have found thousands of phytochemicals that have been shown to reduce cancer risk. These are found in colorful, fragrant, plant-based foods like fruits and vegetables. Eating five to 10 servings of these foods a day has been shown to reduce cancer.

The other thing that’s important is adopting a plant-based diet. That doesn’t mean vegetarian or vegan, but just having the majority of your calories come from plant sources. When you switch to a diet heavy in those phytonutrients, you’ll also get more fiber from fiber-rich fruits, vegetables and whole grains. A diet that is high in fiber, 25 to 35 grams a day, is shown to reduce the risk of cancer developing and recurring.

Jaclyn: One of the things that goes hand in hand with a plant-based diet is a healthier weight, and being at or as close as possible to your ideal body weight also reduces the risk for cancer.

After cancer treatment, we try to encourage eating right and aggressively working toward a healthy body weight. People who can reach that healthy weight after cancer treatment, especially breast cancer, are less likely to have a recurrence of cancer.

What are some unhealthy diet habits that may increase the risk for cancer?

Ali: One thing not to do is just assume that because you’re not eating animal products, that you’re eating a healthy diet. A lot of our processed, packaged junk is meat-free. You really want to focus on consuming whole foods, plant-based foods.

I tell my patients to stay away from that long ingredient list that you can’t even pronounce. Try to eat whole foods the best you can — you know an apple is an apple and an egg is an egg. There’s no ingredient list to it.

Jaclyn: We get this question a lot. People will get a cancer diagnosis and they’ll want to know what supplements they need to start. And they won’t necessarily be interested in addressing changes to their diet; they want to know what pill or powder or drink they can purchase to change their nutrition. The evidence doesn’t support those products. It always comes back around to the whole foods, the fruits and vegetables — not a juice version or a powder version or a tablet. It’s the real-deal food from the garden. That’s what you want to eat.

Anita: When people want to know what foods to avoid, I think we all just tell them to reduce those processed foods. There’s not a long list of foods we tell them they can’t have. We just recommend limiting processed foods and meats.

What are some of your recommendations for people who want to make changes away from processed foods, but who may be overwhelmed with such a big change?

Jaclyn: I’ll suggest two things. First, I’ll suggest that you change your sides right away. A side should be a fruit and a vegetable. No more fries, no more chips, no more salad that consists of cheese, croutons and ranch. It needs to be a whole fruit or a whole vegetable. At least one of each is preferred, and those could be your sides with a meal.

The other thing I’ll say is to pick three big things in your life that you’re going to change today. Maybe that’s cutting out soda, or adding two vegetables and two fruits each day, because right now you eat none. Then in three weeks you’re going to add three more changes, and in three weeks, three more. You’re going to keep building on those changes so that in several months, you have made a lot of changes. Because it’s something you did slowly, and built on over time, it’s become a way of life for you.

When people try to do everything all at once, they get burned out, and they often fail.

Anita: I tend to have patients start with three specific measurable goals. I look at their fluid intake, and deal with that. There might be a physical activity recommendation. But I have them start really simple.

We get patients who are in very different places, from someone who is eating all organic to someone who doesn’t eat any vegetables. So, we tailor our recommendations based on where a patient is, because there is always room for improvement.

What research is being done on cancer and diet?

Ali: One thing being researched right now is the ketogenic diet, which involves abstaining from carbohydrates so that your body uses ketone for fuel instead of glucose. The thing they’re looking at now is whether this diet has benefit for brain tumors.

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Jaclyn: There is some evidence that supports a ketogenic diet for patients with brain tumors, but not all patients with brain tumors. It is a mistake to go on that diet thinking you’re going to prevent a brain tumor. It’s something that should be followed closely by a physician or dietitian, because you are drastically changing the macronutrients in your diet. There can be complications and side effects, and you can increase your risk for other disease if you’re not doing it right.

Ali: The reason other patients with cancer are intrigued by this diet is because of the rumor that sugar feeds tumors. Patients may think, ‘If I quit eating carbohydrates, which break down into sugar, then my cancer is going to shrink and go away.’ As dietitians we know that even if we don’t eat carbohydrates, our body is going to break down the fats and protein into glucose to get the nutrients it needs.

So yes, a tumor needs glucose to grow but so does every cell in our body, and so even if we don’t eat carbohydrates, our body will still find a way to produce that fuel.

What are some diet considerations during treatment for cancer?

Ali: Muscle wasting and weight loss have actually been linked to poor cancer treatment outcomes and increased symptoms with cancer treatment, and so we really push to maintain your weight the best you can during treatment.

Anita: In some studies, even losing 6% of your body weight during cancer treatment was shown to have serious consequences on patient outcomes.

Ali: During treatment, the diet really should be symptom based. If you’re nauseated and the only thing you can tolerate are simple carbohydrates — crackers, light pasta — we want you to eat that because during treatment the main goal is for you to get calories, fuel and nutrition in one way or another.

Anita: We’ll help patients deal with symptoms like nausea, vomiting, diarrhea, constipation, taste issues and others.

Ali: Depending on where a patient is getting radiation treatment, he or she could have different symptoms. We follow patients with head and neck cancer closely, because they may be getting radiation treatment to their throat, and some people lose the ability to swallow. We work closely with patients who may require a feeding tube for nutrition to help meet their nutrition needs.

Anita: With patients who have head and neck cancers, we may be helping them deal with sore throat, sore mouth or dry mouth.

Jaclyn: The caloric demands can sometimes double for patients being treated for cancer. There are things we know ahead of time that will help us determine the level of nutritional support a patient may need, such as whether radiation will be to both sides of the neck, the radiation field, dosage and other things that help us determine the impact on the person.