Does Sugar Feed Cancer?

By Stacy Kennedy, MPH, RD

One of the most common questions we hear from our patients is, “does sugar feed cancer?”  As with most nutrition research, the answer to this seemingly simple question is actually quite complex.

Overall, most of the research in sugar and cancer uses data from preliminary studies with animal and test tube data to draw conclusions. Recent research has looked at the details of an individual’s diet and sugar intake and how it may affect cancer risk or survivorship outcomes, but there have not been any randomized, controlled trials showing that sugar causes cancer.

Let’s look at some information about the link between sugar and cancer and what steps you can take to use healthy eating as a tool to lower your risk.

Should I eliminate all sugar from my diet to reduce cancer risk?

As opposed to an “all or nothing” mentality, reducing sugar intake and boosting nutrient-dense, high-fiber carbohydrates may be most effective.

The optimal diet for cancer prevention and survivorship is similar to a healthy diet for other chronic illnesses like diabetes and heart disease. Looking at the Harvard School of Public Health Healthy Eating Plate, 50 percent of the plate is high fiber fruits and vegetables, with more vegetables than fruits. Protein-rich foods (25 percent) and whole grain carbohydrates (25 percent) can help with regulating blood sugar levels. Adding healthy fats in moderation, like avocado, nuts and seeds can also help stabilize blood sugar.

Can carbohydrates increase cancer risk?

There are many carbohydrates or “starches,” but not all may have the same effect on blood sugar.

Glycemic load (GL) and glycemic index (GI) indicate how rapidly carbs may elevate blood sugar and insulin levels. Generally, a lower GL is preferred, as it will have less of an effect on blood sugar levels and insulin response. Research shows that excess insulin may be a culprit in overall cancer risk or worse survivorship outcomes.

Lower GL foods, such as whole grains and starchy vegetables, tend to provide more vitamins, minerals, fiber and other beneficial nutrients.  Due to their natural carbohydrate structure, fiber and protein, lower GL foods are broken down and absorbed more slowly into the bloodstream, reducing a blood sugar “spike” or dramatic insulin response.  Higher GI foods to limit in the diet include cookies, candy, cakes and other baked or packaged goods like bars, crackers, pastas, and breads made with white flour. Sugar sweetened beverages like soda, fruit juices or specialty coffee drinks should also be limited.

Which types of cancer are most influenced by sugar?  

Studies show that risk of prostate, colorectal and pancreatic cancers may be most influenced by sugar.  One study showed that those who ate a diet high in GL were at a 26 percent increased risk of developing prostate cancer compared to those with a lower GL diet. Similarly, the study showed a high GL diet led to a 44 percent increased risk of rectal cancer and a 41 percent increased risk of pancreatic cancer. Other studies have shown that a diet high in fructose or glucose can increase pancreatic cancer by 25-29 percent.

A team led by Jeffrey Meyerhardt, MD, a medical oncologist with Dana-Farber’s Center for Gastrointestinal Oncology, found that Stage III colon cancer patients undergoing chemotherapy with high GL and higher total carbohydrate intake were more likely to experience worse overall survival than those with low GL, especially in those who were overweight.

Data from the Nurses Health Study also found that the association between colorectal cancer and fructose intake was especially strong in overweight men. While whole fruit naturally contains some fructose, limiting added sugar and fructose like high fructose corn syrup and sugar-sweetened beverages remains important rather than limiting fresh fruit in the diet. Fresh fruit also contains fiber and phytonutrients, which may provide additional immune system benefits as well as regulate blood sugar and insulin response.

How can I limit potential negative effects of sugar?  

It’s important to remember balance and moderation in your diet, as opposed to “all or nothing.”  Having small amounts of something sweet occasionally is unlikely to have a strong effect on cancer risk or survivorship, but fresh fruit can be a healthy substitute and may have cancer preventive and immune supportive properties. Other tips:

• Eat balanced meals and snacks.
• Include a protein-rich and fiber-rich food with each meal and snack.
• Stay well hydrated.
• Include walking and other physical activity regularly.
• Eat plenty of vegetables and other plant-based foods.
• Choose fresh or whole fruit over dried fruits and fruit juices. Add fresh/frozen fruit to plain Greek yogurt instead of purchasing flavored options with fruit already included.
•  Choose whole grains and starchy vegetables like quinoa, brown rice or sweet potatoes over refined grains like white rice, breads and potatoes.
• Use fresh or dried herbs and spices, like cinnamon, to flavor foods and add nutrients.
• Focus on getting adequate sleep and managing stress levels.

Learn more about healthy eating by visiting the Dana-Farber/Brigham and Women’s Cancer Center Nutrition Services website, or by watching our Eating Well During Cancer series. You can also find healthy recipes in Dana-Farber’s Health Library or by downloading our Ask the Nutritionist app.