There are many wise health-related reasons to limit your sugar intake. From dental decay to diabetes, sugar is a dietary culprit that has been proven to contribute to our national obesity epidemic and numerous related diseases, including cardiovascular disease. Yet while being overweight can indeed increase your risk of various types of cancer, it does not necessarily follow that eliminating sugar from your diet will prevent the growth of cancer cells or kill them. This idea that limiting or cutting out sugar can help cure cancer is a myth that is frequently repeated in social media and non-scientific publications. There is no medical evidence that this is true.
What we know is that cancer cells do take up sugars, specifically glucose, and what many people then incorrectly deduce or infer is that because cancer cells take up glucose, then eliminating the glucose will slow the cancer growth. This belief stems largely from a misunderstanding of the Warburg Theory, which was the discovery by Nobel Prize-winning chemist Otto Warburg that cancer cells act as if they are oxygen-starved because they take up and ferment sugars, namely glucose.
The reason cancer cells act as if they are low in oxygen is mostly because, instead of using oxygen for respiration and energy, they use a more primitive form of respiration that converts 6 carbon glucose into the 3 carbon sugars pyruvate and lactate. This is called anaerobic glycosis, which is an inefficient way to create energy that requires a lot of glucose per unit of energy created. The process by which cancer cells feed and grow creates an environment which leads the cells to preferentially take up glucose. But it is not the glucose that causes the cancer to grow.
There have been a large number of clinical studies released on the effects of diet and nutrition on cancer indicating that in some situations low calorie and low fat diets can help prevent cancer recurrence in some breast cancers. However, there is no scientific information that those who reduce sugar alone will receive any benefit.
What I do tell cancer patients is that eating a healthy, balanced diet is good for everyone. Limiting sugar intake is wise and recommended for any number of reasons, including the fact that these are empty calories with no nutritional benefit. But for a patient with advanced cancer, we actually encourage them to eat more, including sweet treats, because weight loss and functional caloric deficiency, inducing a clinical condition called cachexia, is often a serious concern.
For those who would like to dig deeper into the topic of how diet and breast cancer are related, I recommend looking up the Women’s Intervention Nutrition Study (WINS) whose lead investigator was Rowan Chlebowski, MD of Harbor-UCLA. And for those who just want dietary advice, whether you have a cancer diagnosis or not, my recommendation is to eat a sensible number of calories from a variety of healthy foods. Americans in general eat too many calories and too much unrefined sugar which is not good for you, but that’s much different than advising to not eat any sugar at all.