evidence: Myth vs. Truth: Sugar and Cancer [...] You CAN have small amounts of sugar, even after a cancer diagnosis. Sugar does NOT cause cancer. The myth that sugar causes cancer gives sugar a bad name. There are many flavors and foods a person with cancer may not be able to swallow or digest. Weight loss and malnutrition is a concern for many cancer patients. Too many food restrictions—such as completely eliminating foods with sugar—may keep cancer patients from eating enough or cause unnecessary stress. It takes lots of time, energy, and resources to limit all sugar in a menu. Aim for a healthy amount of sugar intake daily—less than 10 percent of your calories.