Reviewed by Dietitian Maria Laura Haddad-Garcia

Key Takeaways

• All of our cells use sugar as an energy source.

• Eating too much added sugar can increase your risk of chronic diseases, including cancer.

• Foods with naturally occurring sugar, such as fruit, have protective benefits from fiber and antioxidants.

Americans love sugar, notably added sugars. We eat a lot of it—like A LOT—to the tune of 17 teaspoons of added sugars a day on average for U.S. adults, mainly in the form of sugary drinks and treats, but also in sneakier foods like protein bars and condiments. That’s 40% more than what’s recommended by the Dietary Guidelines. Eating too much added sugar can negatively impact your health, from causing inflammation to increasing your risk of certain health conditions such as type 2 diabetes. You may also have heard that eating lots of sugar causes cancer, but spoiler alert: it’s not so simple. While diets high in refined and added sugars are linked with higher rates of cancer, the idea that sugar exclusively feeds cancer cells—or conversely, that starving cancer cells of sugar can be beneficial—is a myth.

Cancer affects millions of Americans, with breast cancer, prostate cancer and lung cancer being some of the most common types. While experts aren’t 100% sure what causes cancer, there are many factors—including diet—that may contribute to cancer development. “Chronic consumption of processed foods, particularly those high in refined sugars, unhealthy fats and carcinogenic compounds, can fuel inflammation and oxidative stress—both of which set the stage for DNA damage and cancer growth,” says Steven Quay, M.D., Ph.D., founder of Atossa Therapeutics, a company specializing in innovative breast cancer diagnostics.

Is it possible that our outsized love for added sugars is feeding a cancer epidemic? We dug into the science to find out.

Related: Does Eating Organic Foods Really Lower Your Cancer Risk? Here’s What Experts Say

Understanding Sugar and Its Role in the Body

Sugar is a simple carbohydrate that our bodies rely on for energy. While you can find it in more obvious and not-so-nutritious foods like candy, desserts and soda, it’s also found in nutrient-dense foods like fruits, vegetables and unsweetened dairy. The difference is that sugar is added to foods like soda or candy, whereas it’s naturally found in foods like fruit and milk, meaning these foods don’t affect your body in the same way.

“The sugar in whole foods like fruit comes with fiber, antioxidants and nutrients that slow absorption and help keep blood sugar steady,” says Pam Hartnett, M.P.H., RDN, a cancer recovery coach, dietitian and 15-year cancer thriver. In fact, eating whole fruits and veggies is linked with lower rates of type 2 diabetes, certain types of cancer (like esophageal) and heart disease.

But added sugars—like those in soda and candy—enter your bloodstream very fast, spiking insulin, triggering inflammation and setting off metabolic changes linked to cancer, explains Hartnett. In fact, eating too much added sugar is linked with chronic health issues like type 2 diabetes and heart disease.

Not all added sugars are the same when it comes to cancer risk. “Fructose, particularly in the form of high-fructose corn syrup, is uniquely problematic. Unlike glucose, which can be metabolized by nearly every cell, fructose is processed primarily in the liver, where it promotes fat accumulation, insulin resistance and inflammation—key cancer risk factors,” says Quay.

The Link Between Sugar and Cancer

“Cancer is a complex disease, but we now understand that certain lifestyle and environmental factors can significantly increase the risk of developing it,” says Quay. Some risk factors include a diet lacking nutrients, metabolic syndrome, tobacco or alcohol use, exposure to environmental toxins and radiation, and chronic inflammation.

Related: Is It Time to Rethink That Drink? What the Latest Science Says About Alcohol & Your Health

While sugar doesn’t directly or exclusively “feed” cancer, cancer cells do metabolize sugar—a phenomenon called the Warburg effect. “Cancer cells take up glucose at a far higher rate than normal cells, feeding their rapid growth,” explains Quay. “The Warburg effect underscores the critical role of sugar metabolism in cancer. While normal cells can adapt to various fuel sources, cancer cells are far more dependent on glucose.”

While sugar itself doesn’t cause cancer, cancer cells do rely on sugar to expand (like normal cells do). Scientists believe that sugar may also contribute to cancer development through other pathways as well: chronic inflammation and by disrupting insulin production and the gut microbiome.

Increases Inflammation

Research has shown that excessive added sugar intake increases chronic inflammation (a low-grade, long-term type of inflammation) in the body. “The metabolism of sugar creates pro-inflammatory byproducts. As inflammation goes up, so does cancer growth,” says Daniel Landau, M.D., a physician who is board-certified in medical oncology, internal medicine and hematology. Why? “Over time, this [inflammation] weakens the immune system, making it harder to find and remove abnormal cells before they become cancerous,” says Hartnett. In fact, anti-inflammatory drugs are being explored as a means of treating cancer by shrinking tumors.

Impacts Insulin Production

Another way sugar affects cancer development is via unstable blood sugar and insulin levels. “Frequent blood sugar spikes and high insulin levels can create conditions where cancer thrives,” says Hartnett. Research shows that having diabetes (both type 1 and type 2) can increase your risk of developing certain types of cancer, such as liver, pancreas and kidney.

“High sugar consumption leads to spikes in insulin and insulin-like growth factor 1 (IGF-1), both of which promote cell growth—including cancer cells,” says Quay. It also leads to insulin resistance, where insulin isn’t as effective at moving sugar from your blood to your cells. All of this is linked with increased chronic inflammation and a higher risk of cancer.

Alters Your Gut Microbiome

Eating excess added sugar or having high blood glucose (sugar) levels may disrupt your gut microbiome—the community of microorganisms that live in your digestive system. “Excess sugar alters the gut microbiome, favoring pro-inflammatory bacteria that create an environment conducive to tumor development,” says Quay.

Your gut microbiome doesn’t just impact gut health; it also plays a big role in your immune health. “Because the gut plays such a key role in immune health, an imbalance in gut bacteria can make it difficult for your body to detect and eliminate abnormal cells before they turn into cancer,” says Hartnett.

How Much Sugar Is Safe?

Most nutrition recommendations include limits for added sugars but not for total sugars. That’s because sources of natural sugar like fruits and veggies are nutrient-dense and encouraged for overall health.

Different health organizations have slightly different recommendations for added sugars. For instance, the 2020-2025 Dietary Guidelines for Americans recommends limiting added sugars to no more than 10% of your total calorie intake. For a 2,000-calorie diet, that’s about 12 teaspoons of sugar or 50 grams. Yet, the American Heart Association’s limits are stricter. They recommend that no more than 6% of your calories come from added sugars. For a 2,000-calorie diet, that’s about 7 teaspoons or 30 grams per day. The American Cancer Society doesn’t have specific recommendations for added sugar. Instead, they recommend eating an overall healthy diet with minimal added sugars.

Unfortunately, as mentioned above, U.S. adults consume an average of 17 teaspoons of added sugar daily—over 40% more than the Dietary Guidelines’ recommendations. The most common sources of added sugar are sugar-sweetened beverages (like soda or sweetened tea), desserts and sweet snacks like cookies, brownies, doughnuts and ice cream.

While these are ​​obvious sources of added sugars, some sneaky ones include condiments, sauces, protein bars, yogurt, granola, canned fruit and nut butter. Added sugar may appear on the list of ingredients as glucose, fructose, dextrose, sucrose or maltose. Notice a trend? Most ingredients that end with “-ose” are added sugars. Also, keep in mind that sugar, syrup, molasses, honey and agave all count toward your total added sugar intake.

Tips for Reducing Sugar Intake

So, should you ditch sugar entirely to reduce your cancer risk? Not necessarily! “When I starve the ‘cancer cells’ of glucose (sugar), I’m also starving the healthy cells as well, making it difficult to thrive during treatment. Depriving your body of glucose can lead to fatigue, muscle loss and slower recovery—none of which are helpful when you’re fighting an illness,” says Baham.

Plus, Hartness says, “Cutting [sugar] out completely often leads to stress, cravings and an unhealthy relationship with food—none of which support long-term health.”

“The key is moderation,” adds Baham. “Rather than fearing sugar, focus on limiting added sugars in sodas, sweets and ultra-processed snacks while maintaining a balanced, nutrient-dense diet,” she says.

So, how can you minimize sources of added sugar in your diet? Here are some ideas:

• Prioritize whole fruits over juices, since they contain fiber.

• Gradually reduce sugar or honey in your coffee and tea.

• Read the Nutrition Facts panel to choose condiments, yogurts, drinks and sauces with fewer added sugars.

In addition to limiting added sugar, it’s important to eat a balanced diet rich in plant-based foods (think veggies, fruits, whole grains, legumes and nuts), lean proteins and heart-healthy fats. This can help prevent cancer and other chronic diseases.

The Bottom Line

While sugar (glucose) feeds all the cells in your body, the idea that eating sugar directly leads to cancer cells is just a myth. However, eating too many added sugars can increase your risk of developing cancer through increasing inflammation and insulin production and altering your gut microbiome. That said, it’s important to note that added sugars aren’t the same as naturally occurring ones. As the name implies, the latter are naturally found in foods like fruits, vegetables and unsweetened dairy, which contain other nutrients like fiber and antioxidants, providing protective effects against diseases. So, rather than cutting out sugar entirely, focus on opting more frequently for these foods that can help prevent cancer and promote overall health. 

Read the original article on EATINGWELL