Sugar's Role in Cancer

Nov 30, 2023 | Linde Sifuentes, Patient Educator | @sifuenteslinde

Article contributed by Mayo Clinic dietitian, Jackie See

Sugar seems to be a major source of anxiety and fear for people with cancer. There is a myth circulating that sugar feeds cancer and that avoiding sugar will prevent the growth of cancer. To set things straight…sugar does not cause cancer on its own. Giving sugar to cancer cells does not make them grow faster and depriving cancer cells of sugar does not make them grow more slowly. However, sugar may be indirectly involved in the development of cancer.

How it happens

Much research shows that it is sugar’s relationship to overweight and obesity that may influence cancer cell growth the most. Sugar is a major source of extra calories, which can contribute to weight gain and obesity, but it’s not just sugar. Too many calories from any source - carbohydrate, fat and even protein – can lead to weight gain. Extra weight not only increases the risk of diabetes and heart disease but is also a risk factor for 13 different cancers.

One of the ways excess weight can lead to cancer is through insulin resistance and insulin-like growth factors in the blood. Both excess weight and lack of physical activity can lead to an increased risk of insulin resistance. Although insulin resistance can also be hereditary, it usually happens when the overweight body can no longer make enough insulin to remove sugar from the blood. Exercise also helps remove sugar from the blood.

Blood sugar and insulin levels in lean, active people usually stay in a healthy range regardless of what they eat. Sugar provides only empty calories and no other nutrients. Nutrition guidelines encourage all of us to cut down on added sugar because it is such a big source of calories in the American diet. The Dietary Guidelines for Americans recommend no more than 10% of our calories from sugar. On a 2000 calorie per day diet, this would be 50 grams or 12 tsp of added sugar. The American Heart Association recommends limiting added sugar to 25 grams (6 tsp) per day for women and 37 grams (9 tsp) per day for men. This adds up quickly if you drink sweetened soft drinks or eat candy and desserts on a regular basis. For example, a can of Coke contains 29 grams (7 tsp) of sugar and an average size Hershey bar, 24 grams (6 tsp). Even healthy foods can contain significant amounts of added sugar. A 6-ounce container of low-fat yogurt may contain up to 15 grams (4 tsp) of added sugar and a Nutri-grain bar contains 12 grams or 3 tsp.

Excess body fat also produces other substances that contribute to the development or growth of certain cancer types. Fat cells produce estrogen, which can fuel breast and endometrial cancers. Fat cells produce other growth factors and cause inflammation that can coax the development and progression of cancer.

Your risk of insulin resistance and other causes of weight-related cancers can be reduced by maintaining a healthy weight and staying physically active. If you are overweight, even losing 10% of your weight can help. Talk to your medical team about your risks for cancer or recurrence of cancer. If you are at a healthy weight, try to maintain that weight. Also try to get a minimum of 150 minutes of physical activity each week.

If you are curious, here is a list of cancers that are linked to obesity: