During the eight years that Stacy Shawhan has worked as an oncology dietitian, she has heard many questions from her cancer patients about how their diet influences their prognosis.
But one question has arisen more than the others: Will consuming sugary foods and drinks feed my cancer cells, worsening my condition?
"Cancer patients are very vulnerable and some are terrified of eating," says Shawhan, who practices at the University of Cincinnati Cancer Center.
"They think, 'If I stop eating sugar, I'll be able to starve my cancer.'"
The narrative that "sugar feeds cancer" dates back to the 1920s, when a German physiologist observed that some tumor cells consumed more glucose than healthy ones.
Soon after, low-sugar diets emerged that claimed to cure cancer.
Recent surveys conducted in the United States and Europe suggest that about one-third of cancer patients actively avoid sugar.
Although experts claim that diets high in added sugars can increase the risk of cancer throughout life, eliminating all sugars does not really fight existing tumors.
"All cells need glucose, so does our brain," says Philipp Scherer, a diabetes researcher at UT Southwestern Medical Center in Dallas.
In other words, the best way to eat if you have cancer – or are trying to reduce your risk of developing it – is with a balanced and healthy diet.
The Role of Sugar in Cancer Risk According to Scherer, sugar is not a carcinogen.
There is no evidence to show that eating sugar causes cancer by itself (as it would, for example, smoking cigarettes).
In addition, Scherer added, "many cancers prefer to use fat as their main source of energy, so even the idea that cancers prefer glucose is not entirely true."
Still, a limited but growing body of evidence has linked excessive consumption of added sugars (the kind found in cookies, cakes, and soda) to cancer.
For example, a large review of studies published in 2018 cited several linking consumption of added sugar and sugary drinks to an increased risk of cancer.
Excessive sugar consumption has been shown to trigger chronic inflammation in some people, which can damage cells that can then become cancerous, Shawhan said.
Excessive consumption of added sugars has also been shown to reduce immunity, which can facilitate the spread of cancer cells.
In addition, excessive sugar consumption can alter metabolism in such a way that it can lead to obesity and diabetes, diseases that are known to increase the chances of getting cancer.
According to Shawhan, once cancer is diagnosed, eliminating sugar does not seem to slow or stop its growth in most cases.
"At this point, it's not sugar intake that's driving cancer growth, it's the cancer itself."
In addition, sugar is essential for most living things, Scherer said.
And when it's produced naturally in foods like dairy products, fruits and vegetables, it's part of a healthy diet, said Natalie Ledesma, an oncology dietitian at the UCSF Helen Diller Family Comprehensive Cancer Center.
For the most part, experts agree that you don't need to abstain from sugars that appear in whole foods.
But Ledesma notes that excessive consumption of added sugars has been associated with worse outcomes — including higher death rates — in patients with certain solid tumors, such as breast, colon and prostate cancer.
It can also affect other types of cancer, but research on rarer ones is limited.
Dr. Santosh Rao, an integrative oncologist at Connor Whole Health University Hospitals in Cleveland, says it's also important for cancer patients to control their diet without being afraid of food.
Up to half experience loss of muscle mass as a result of the disease.
And sometimes things doctors recommend to patients during rounds of grueling treatments — such as Ensure, electrolyte drinks or even potatoes — can contain a lot of sugars, Shawhan said.
Although everyone should avoid diets high in added sugars, cancer patients with certain metabolic diseases should be especially vigilant, because those diseases can affect their prognosis.
"For example, patients with poorly controlled diabetes tend to have more aggressive breast cancer," Rao said.
And a meta-analysis suggested that obese patients were more likely to die from colon, breast and uterine cancer.
How to eat healthier without depriving yourself of anything The best way to reduce your risk of cancer, and to eat if you have been diagnosed with the disease, is to follow a healthy diet that contains plenty of whole fruits and vegetables.
Some studies show that Mediterranean diets meet these goals and help reduce the risk of cancer.
Combining carbohydrates with protein, fiber, and fats (for example, a little peanut butter on an apple slice) prevents glucose spikes that, over time, can wreak havoc on our metabolism and increase the risk of cancer.
In general, according to Shawhan, it's okay to consume a little added sugar, even on a daily basis, as long as you get the essential nutrients from the rest of your diet.
It recommends not exceeding the 12 teaspoons of added sugar a day suggested by the U.S. Department of Agriculture, or better yet, follow the recommendation of six teaspoons of the World Health Organization.
Research on sugar substitutes and their influence on cancer and cancer risk is inconclusive.
Experts suggest avoiding them until we know more.
Ledesma prefers, instead, to sweeten his recipes with naturally sweet foods, such as bananas, frozen berries and applesauce, which frequently appear in his non-dairy ice cream.
"Cinnamon or ginger provide sweetness without adding calories or sugar," explains Ledesma.
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