The idea that sugar feeds cancer has been circulating in mainstream media for decades. Its origins go back to a paper published in the 1920s by Otto Warburg, a German chemist who, along with his colleagues, found that tumors take up large amounts of glucose, which is then converted into lactate rather than going into the mitochondria and converted into energy and carbon dioxide.

His ideas would come to be known as the Warburg effect in the 1970s. So the theory goes that if we “starve” the cancer cells of glucose we can stop the growth of the tumor and potentially destroy the tumor. We have learned a lot since then about how cancer cells get and use energy for growth and, looking at more recent evidence, we can say it’s not as simple as “starving” the cancer cell of glucose.

Healthy bodies need energy to function properly. Without energy, we can’t produce new cells, repair damaged cells, maintain our organ systems, and support a robust immune system. Unlike plants that use sunlight to make energy (glucose), humans have to eat food to consume energy in the form of macronutrients such as fats, proteins, and carbohydrates to then be used to produce energy.

Humans can use all three of these macronutrients to produce energy, but our bodies prefer glucose as its main energy source under normal, healthy conditions. Cancer cells are no different in that in order for them to grow and reproduce, they also need glucose to supply their energy needs. If we avoid consuming sugar from carbohydrates, our stores of glucose will drop to critical levels and so our bodies will begin breaking down more protein and fat to ensure our blood glucose remains stable. This increased breakdown of protein results in muscle loss and a weakened immune system.

In the absence of glucose, the breakdown of protein and fat in a healthy body and in a body that has cancer. So, if we reduce or eliminate glucose from a healthy well-balanced diet, this impairs our own healthy cells from getting the energy they need to survive and thrive.

Studies have shown that this elimination of glucose from the diet will not slow the growth of tumors. More scientific evidence is needed to better understand if and how a ketogenic diet helps slow tumor growth, we currently do not have enough evidence to support eliminating carbohydrates from our diets in hopes of reducing or slowing the growth of tumor cells.

So, is there a sugar and cancer connection?

When we eat, our glucose levels rise which triggers the pancreas to produce insulin. Insulin is a hormone that helps glucose move from our blood into our cells, bringing our blood sugar levels back to a normal range.

When we consume large quantities of simple sugars (i.e., the form that is closest to what our bodies absorb), blood glucose levels spike, and more insulin is released to account for it. If a person consumes a diet that is high in simple sugars for several decades, our insulin levels can be abnormally high and, over time, our cells don’t respond to the insulin as well and the glucose remains above normal levels in our blood. This can lead to a syndrome called hyperinsulinemia (high circulating insulin levels) and eventually insulin resistance and Type 2 Diabetes, both of which are pro-inflammatory diseases – a potential driver for cancer progression.

Insulin resistance can alter your body’s production of certain proteins, which subsequently increases levels of free estrogens and androgens in the body, and can increase the risk of some cancers like breast cancer.

Another way sugar is connected to cancer is through obesity. A highly processed diet is often high in added sugars, resulting in weight gain. Obesity is considered a low-grade inflammatory state and one of the hallmarks of cancer is chronic inflammation. A 2014 policy paper by the American Society of Clinical Oncology (ASCO) noted that “obesity is a major under-recognized contributor to the nation’s cancer toll and is quickly overtaking tobacco as the leading preventable cause of cancer.”

Angelea Bruce, RD, CSO, CNSC, oncology dietitian for Sharp Healthcare in San Diego, uses this analogy for helping her patients better understand the role of sugar and cancer.

“Every cell in the body requires glucose for fuel, including cancer cells.

We get glucose from all carbohydrate foods. If we don’t eat enough carbohydrates, the cells (normal and cancer) still demand a source of glucose and the body makes it by breaking down protein from our muscles and immune system. In order to minimize muscle loss and immune compromise, we need to provide a consistent source of carbohydrates through the diet whenever possible.

Cells use glucose the way cars use gas. With normal driving, our car uses varying amounts of gas depending on whether we are idling or accelerating. Normal cells divide at varying rates, some every three days and some every three months, or more. During cell division, more glucose is used, much like an accelerating car uses more gas. But after cell division, it returns to more of an idling state, using less glucose.

Cancer cells are like cars with the accelerator stuck to the floor, using glucose at high rates, because they are dividing at much faster rates than normal cells. If you still want to be able to drive your car, you cannot fix it if it has the accelerator stuck down simply by letting it run out of gas. For the same reason, you cannot starve cancer cells of glucose because you will also be depriving your healthy cells of fuel. The cancer cells are much more tenacious than the normal ones and will persist at the expense of the rest of the body.”

Bottom Line

Sugar (glucose) comes from all carbohydrate foods. Our bodies don’t control which cells get glucose. Our recommendation is to consume a mostly whole food diet that is abundant in plant foods such as fruits, vegetables, whole grains, and legumes. Minimize the amount of highly processed foods as possible and maintain a regular schedule of physical activity.

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Kate Ueland, MS, RD, specializes in oncology nutrition, primarily working with breast, ovarian, renal, and melanoma cancer patients throughout all stages of the cancer journey at Seattle Cancer Care Alliance (SCCA) in Seattle, WA. As Cook for Your Life’s nutrition advisor and editor, Kate ensures all culinary content adheres to the Academy of Nutrition and Dietetics and follows science-based guidelines.