Sugary foods are plentiful in the modern Western diet. Do they increase one's cancer risk?
One of the most misunderstood topics in the complex interplay of food, obesity, and cancer is sugar.
The internet is full of misrepresentations and half-truths that lead many people to incorrectly believe that sugar directly causes cancer — or even that cancer can be treated by cutting off sugar to “starve” it.
Santosha Vardhana, MD, PhD, is a physician-scientist who treats people with lymphoma and studies how cells use nutrients. Christina Stella and Cara Anselmo are registered dietitian nutritionists at Memorial Sloan Kettering Cancer Center (MSK).
They explain the real science of sugar and cancer.
What does the evidence say about whether eating sugar causes cancer?
Dr. Vardhana: There is a clear link between obesity and several forms of cancer. And eating too much refined sugar in highly processed foods can lead in the long term to health issues, including obesity, that put you at higher risk of cancer.
MSK lymphoma specialist Dr. Santosha Vardhana
But if you starve yourself of sugar, will you strongly reduce your risk of cancer? The short answer is no.
What does cause cancer?
Cancer happens because a cell in your body grows out of control with no guidance from your DNA, like a car that just keeps speeding up. Environmental factors and diet can play a role. But more commonly it’s caused by known carcinogens like ultraviolet light, radiation, smoking, or alcohol. And sometimes it’s just bad luck, essentially — there isn’t always a specific cause. So you could never starve your body enough to prevent it from developing cancer.
Is the fructose in fruit better than other sugar?
Cara Anselmo: A related thing we hear from people, including those in treatment, is that because fruit has fructose — a kind of sugar — that they should avoid eating fresh fruit. That is a myth we want to dispel. Eating a plant-forward diet that incorporates fruits and vegetables in their whole-food form, in practical portions, is actually a smart way to reduce the risk of cancer developing
MSK clinical dietitian-nutritionist Cara Anselmo
or recurring.
If you are diagnosed with cancer, can you treat it by not eating sugar?
Dr. Vardhana: No. Cancer does consume sugar. But people often misinterpret what that means.
Cancer will eat sugar if it’s around. But cancer will eat anything in your body: protein, fat, even dead cancer cells. If you try to starve cancer of one thing, such as sugar, it will eat something else. Your body will always lose a race to starve cancer because cancer is programmed to grow without stopping no matter the conditions.
People also need to understand that because cancer is such a serious disease, the therapies to treat it need to be powerful. Harsh starvation diets are more likely to have bad effects on the treatments you need rather than hurting the cancer.
Nobody is saying you should eat to excess or go to McDonald’s for every meal. But you should eat sensibly to keep your body as fit and strong as possible.
What does healthy eating look like during cancer treatment?
Dr. Vardhana: We’re at the very infancy of figuring that out. I urge my patients to eat a Mediterranean diet, meaning whole fruits and vegetables, lean proteins, and carbs that are complex, because the body has to put in some work to break them down. That means limiting ultraprocessed foods.
Christina Stella: As dieticians, we’re very focused on the needs of each individual. Some people find eating and drinking so challenging during treatment because of side effects such as nausea and fatigue that we will take two chocolate chip cookies over nothing at all.
In other cases, a low-fiber diet might be appropriate for people who experience gastrointestinal problems during treatments like immunotherapy. Nutritional needs can also change during treatment. That is why it can be so helpful to work with a dietitian.
MSK clinical dietitian-nutritionist Christina Stella
Cara Anselmo: I work with many women with breast cancer, and a common side effect of some treatments is weight gain. That surprises many patients who expect that chemo and radiation will make them lose weight.
We work together to identify areas where they can modify their eating habits. One source of added calories might be sweetened drinks like soda. If they drink one a day, can we figure out how to get that to once a week? Or can we limit how often they eat baked goods or other sweet snacks? We’re also mindful that emotions play a big role in eating, particularly during cancer therapy. That’s normal and nothing to be ashamed of.
Dr. Vardhana is a Josie Robertson Investigator.
