It’s a question doctors and dietitians hear from many women: Does eating sugar cause breast cancer? Can it raise your risk or make a tumor grow faster?
Major medical groups such as the American Cancer Society insist it’s a myth that “sugar feeds cancer.” Scientists are still looking into the link between sweets and all forms of the disease, including breast cancer, which affects about 1 in 8 women in the United States. But some research may offer a reason to rethink your sugar intake.
Is It Sugar or Weight Gain?
The typical American adult gets about 34 teaspoons of sugar every day, more than three times the maximum amount recommended by the U.S. Department of Agriculture’s dietary guidelines.
Sugar is a simple carbohydrate and comes in several forms, including fructose, glucose, sucrose, and lactose. (High-fructose corn syrup, which is used in sodas, baked goods, and other processed foods, is a mix of fructose, glucose, and water.)
Complex carbohydrates are found in starchy foods, such as bread, pasta, and vegetables. During digestion, your body breaks down complex carbs into simple sugars, including glucose. So-called high-glycemic carbohydrates, such as potatoes and white rice, change to glucose quickly in the bloodstream. Cells absorb glucose and use it to make energy.
Cancer cells use a lot of glucose: about 200 times more than normal cells. That discovery in the 1920s helped give rise to the idea that “sugar feeds cancer,” but many dietitians say that’s too simplistic. “There’s no direct link between sugar and breast cancer,” says oncology dietitian Nichole Giller, who works with people who have cancer.
But that’s not a green light to fill up on chocolates and root beer. Sugar is high in calories, and eating too much causes weight gain. That leads to extra body fat, explains Giller. And fat is a source of the hormone estrogen, which raises the risk for breast cancer at high levels.
But Giller counsels that focusing on sugar alone is a mistake. “Eating too much of any food can cause an increase in weight, which will increase your risk for breast cancer,” she says. “It’s not just sugar.”
Sugar, Insulin, and Breast Cancer
Some doctors take a different approach. “I tell people that they should reduce sugar consumption and carbohydrate consumption,” says Victoria Seewaldt, MD, chair of the Department of Population Sciences at City of Hope, a cancer research and treatment center near Los Angeles.
Seewaldt, who studies cancer prevention, has long been interested in the link between breast cancer and the hormone insulin. Your pancreas makes insulin to help your body store glucose broken down from carbohydrates in cells in muscle, fat, and other tissues. Eating a lot of sugar and other carbohydrates raises blood sugar levels and insulin production.
Breast cancer is a complex disease involving a number of factors, Seewaldt says, including insulin. She explains that insulin helps stimulate a number of biological changes in the body that are known to promote breast cancer. “Insulin is a really bad actor,” Seewaldt says.
Studies Are Mixed
Research suggests that certain foods affect the risk for breast cancer, says Heather Eliassen, ScD, an associate professor of epidemiology at the Harvard T.H. Chan School of Public Health and associate professor of medicine at Harvard Medical School and Brigham and Women’s Hospital in Boston, who studies breast cancer and lifestyle. For instance, diets high in fruit and vegetables (especially brightly colored produce) seem to reduce the risk, especially for aggressive forms of breast cancer.
But scientific studies haven’t consistently shown that getting too much sugar makes you more likely to develop breast cancer, Eliassen says. For instance, her research suggests that young women who eat or drink lots of foods and beverages high in sugar and high-glycemic carbohydrates don’t appear to have a higher risk for breast cancer. She and her colleagues are studying whether that’s true in middle-aged and older women. Yet one other study has found that women who drink a lot of sugary beverages may have a higher risk.
But Eliassen thinks that eating lots of sugar may be a bad idea if a woman has breast cancer. She and her colleagues recently published a study showing that women diagnosed with breast cancer who have diets rich in high-glycemic foods, including sugary foods and beverages, are more likely to die of the disease or any other cause. In another study, Eliassen’s team found that women with breast cancer who drink a lot of sugary fruit juice (other than orange juice) also had lower survival rates. This research also showed that women with breast cancer who eat a lot of fruit and vegetables may have better survival rates.
It’s possible that sugar, or the rise in insulin that happens when your body processes it, does contribute to tumor growth, Eliassen says. “Tumors require a lot of energy,” she says. “If you’re giving them easy access to energy in the form of glucose in the blood and growth factors in the form of insulin, that may possibly explain a way in which your diet could cause a tumor to spread.”
But if you’re concerned about breast cancer, especially if you’ve been diagnosed with the disease, Eliassen encourages thinking broadly about what to eat instead of focusing on a single ingredient. “A well-rounded, healthy diet is fantastic for a number of reasons,” she says. “And one of the benefits may be that you have better survival if you develop breast cancer.”