In 2007 there was an e-mail sent by ‘John Hopkins [sic]’ that made an alarming claim: if you eat sugar, it will feed your cancer. The email was a fake and has since been debunked by the real Johns Hopkins (note the ‘s’ at the end of ‘Johns’), but the idea had already spread. When I sat down to write this post, I typed the phrase “Does sugar feed cancer?” into Google and turned up over 654,000 hits. There have been books, cable news discussions, and thousands of web articles on this topic, but support for the idea that sugar feeds cancer is murky at best.
So, does sugar feed cancer? This is the number one question that my patients ask me and the answer is complicated. Sugar does feed cancer, but that’s because sugar feeds every cell in our bodies. We get sugar or carbohydrates from simple sugars, like white table sugar, and more complex carbohydrates that come in fruits, vegetables, and whole grains. Whether we eat plain sugar, simple carbohydrates, or complex carbohydrates, our body will turn almost all of these carbs into glucose for our body to use as energy. Everyone needs a certain amount of carbs for healthy cell function, especially for brain function. If you are undergoing cancer treatment, your healthy cells will need energy as cancer saps up resources. Many cancer types require more calories than usual, but sugar and carbs feed our whole bodies—you cannot pick and choose which cells get which fuel.
Carbs come from two primary sources: our food and our body stores. If you don’t eat carbs or sugar, then your body will start breaking down protein from your muscles and fat from your fat stores to create the energy it needs. This will weaken your immune system and potentially hurt your cancer treatment. It’s similar to when a woman gets pregnant. If a woman is pregnant and doesn’t get enough carbs to provide nutrition for her baby, her body will tap into her reserves. Ultimately the baby will take nutrition from the muscles and fat stores if the mother is not eating enough food, which is what happens if you don’t eat enough carbs during cancer treatment to support your healthy cells. To minimize this, we need a consistent supply of carbs throughout the day with each meal.
The problem about blanket statements that tell cancer patients that eating sugar will feed cancer is that it creates fear and pushes people to an extreme way of eating. I’ve had patients refuse to eat fruit because they are “high carb,” but then they miss out on healthy phytochemicals, vitamins, minerals, and fiber that fruits contain. I’ve had other patients eliminate breads, pastas, rice, starchy veggies, beans, dairy, and whole grains. There really isn’t much left to eat at this point besides meat, eggs, fish, and non-starchy veggies. These patients often end up malnourished, and their bodies begin to drain muscle and fat reserves to get the energy it needs. I’ve had patients who needed to put their treatments on hold until their nutrition status improved because they could no longer tolerate their therapies, as they were too weak.
Another unfortunate result of a rigid diet avoiding carbs is that it results in guilt when someone eats a piece of cake to celebrate a birthday or have a desert after a meal with friends. Imagine how stressed out, anxious, and guilty you would feel if you thought that you made your cancer worse by eating a single chocolate chip cookie or a banana? I’m a big advocate of eating healthy as much as you can, but no one should feel bad if they have a small slice of cake on a birthday or for a celebration. Fighting cancer is as much about maintaining positive mental health as it is about maintaining nutritional health.
This is not to say that watching sugar in your diet is a bad thing. Eliminating excess added and processed sugars from your diet is great for most people, and it’s a good idea to become more aware of high sugar foods. I recommend that people try to include more complex carbs in their diets and avoid simple carbs. Complex carbs are foods that are high in fiber, phytochemicals, vitamins, and minerals such as fruits, vegetables, beans, and whole wheat bread, sprouted breads, brown rice, and wheat pasta. The simple carbs are white sugar, desserts, sodas, candy, and white breads, white pastas, and white rice. These are devoid of fiber and most nutrients.
Processed sugar is a relatively recent invention when it comes to human diet, and there are known links between high-sugar diets and diseases like diabetes and obesity. There is a growing area of research looking into how processed sugars affect cancer risks and treatment. High sugar diets can increase our insulin production, which may affect tumor growth. Insulin tells our cells to grow. Some researchers speculate that this could cause cancer cells to grow more. At this point in time there just isn’t enough research or studies to know how insulin and cancer are related. We do know that too much sugar and too much insulin are not good for anyone’s health. So continuing to avoid processed sugars is a good thing.
In the end, there is partial truth that sugar feeds cancer, but that does not mean sugar and carbohydrates should be avoided at all costs. Extreme diets can hurt cancer treatment if they result in malnourishment, cause patients to avoid healthy fruits, starchy vegetables, beans, and whole grains or lead to guilt. Try to eat more foods that have complex carbs, and avoid processed sugar whenever you can—but don’t put don’t put down that bite of delicious chocolate cake when you decide to treat yourself once in a while.