I’ve heard that some types of cancer feed on glucose (the sugar in our blood) and I know of a few people that started a ketogenic diet as adjunct therapy to be used along side surgery and chemotherapy in the treatment of glioblastoma (a form of aggressive brain cancer), but just came across an article that explains why limiting sugar intake can lower one’s risk of cancer. In this article, I explain one biological link between cancer and sugar.
A “Master Switch for Cancer”
In the 1980’s, Dr. Lewis Cantley was a Professor at Tufts University School of Medicine in Boston when he identified a previously unknown enzyme known as phosphoinositide-3-kinase, or PI3K which turned out to a type of ‘master switch for cancer’.
PI3K’s normal function is to alert cells to the presence of the hormone insulin; resulting in the cells pumping in glucose to be used as metabolic fuel for the cell. Signals from PI3K are necessary for normal cell growth, survival and reproduction, however when this enzyme is hijacked by cancer cells, it provides tumors with an over-abundant supply of glucose, which results in their rapid proliferation.
The gene that codes for PI3K is now thought to be the most frequently mutated cancer-promoting gene in humans and is believed to be associated with 80% of cancers, including those of the breast, brain and bladder.
In 2012, Dr. Cantley became the Director of the Sandra and Edward Meyer Cancer Center at Weill Cornell Medicine, which is the biomedical research unit and medical school of Cornell University, where he is Professor of Cancer Biology. In his work at Weill Cornell, Dr. Cantley has continued to investigate the role of PI3K.
Challenges with some anti-cancer drugs that have been developed that block the PI3K enzyme is that these PI3K-inhibitor drugs are designed to starve the cancer cell of glucose, but also signal the person’s liver that their body is starving for glucose, too. As a result, the liver would break down glycogen (a storage form of glucose) and send large amounts of glucose into the person’s blood, resulting in their blood sugar spiking and triggering their pancreas to release lots of insulin, as a result. The presence of all of this glucose from the liver and insulin from the pancreas resulted in these patient’s tumors continuing to grow.
Dr. Cantley and his colleagues wondered whether the spike in insulin from the breakdown of glycogen might be countering the effect of the PI3K-inhibiting drugs by reactivating the PI3K pathway in the cancer cells. Studies first tried giving these patients Diabetes medications to lower their blood sugar and insulin levels, but this didn’t work nearly as well as what they tried next.
The researchers came up with a theory that a ketogenic diet (a diet that is very low in carbohydrate) could prevent the spikes caused in blood sugar by the PI3K-inhibiting drugs and might help the drug starve the tumor, while the patient’s blood sugar remained normal because the body would be fueled by breaking down fat and protein for ketones.
They tested the theory using genetically engineered mice that developed pancreatic, bladder, endometrial and breast cancers and treated the mice with a new PI3K inhibitor drug. The study demonstrated that spikes of insulin did indeed reactivate the pathway in tumors, countering the anti-cancer effect of the drug. However, when the researchers put the mice on a ketogenic diet, in addition to the medication, the tumors shrank. The results were published in the journal Nature in July 2018.
Dr. Cantley explains the biological connection between cancer and sugar this way;
“Our pre-clinical research suggests that if somewhere in your body you have one of these PI3K mutations and you eat a lot of rapid-release carbohydrates, every time your insulin goes up, it will drive the growth of a tumor. The evidence really suggests that if you have cancer, the sugar you’re eating may be making it grow faster.”
Some Final Thoughts…
A normal cell function requires the enzyme PI3K that results in the cell pumping in glucose to fuel growth and reproduction and a cancer cell that has a defect in the gene that codes for PI3K may do the same thing. Sugar, in and by itself does not cause cancer, but in those that have a few abnormal cells, sugar can drive the process of tumor development.
According to the World Health Organization, the average American consumes 126 grams of sugar a day, more than people in any other country and the average Canadian eats almost 90 grams (89.1) of sugar per day. Sugar is not required in the diet; in fact, there is no essential need to eat carbohydrate at all, if people eat adequate amounts of healthy fats and protein.
Given that as many as 88% of Americans are already metabolically unhealthy — with likely a smaller percentage of Canadians following suit (due to slightly lower obesity statistics), there is no valid reason* for the average American or Canadian to be eating foods with added sugar. As I’ve written about in many previous articles, high blood sugar and high insulin levels already predispose people to Type 2 Diabetes and obesity and as outlined in this article, are involved in the proliferation of some types of cancer cells.
*(update April 29, 2019): While I say above that there is “no valid reason” for those who may already be metabolically unwell to eat foods with added sugar – in retrospect, this is not well worded. I think there are lots of valid reasons for people to eat foods with added sugar, but believe that it may be preferable for those who are already metabolically unwell to limited added sugars.
It would seem to me that a prudent approach for metabolically healthy people (12% of Americans, and perhaps an estimated 25% of Canadians) is to stay healthy by avoiding processed foods that are high in refined carbs and sugar, as well as foods high in “natural sugar” such as 100% fruit juice in order to reduce the risk of becoming metabolically unwell or inadvertently feeding malignant cells that feed on glucose.
For the large majority of those that are already metabolically unhealthy, a well-designed low carbohydrate diet can help you reverse the symptoms of Type 2 Diabetes, putting the disease into remission, as well as achieve and maintain a healthy body weight. Not inadvertently feeding tumor proliferation seems like a nice ‘side benefit’, too.
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Crawford A, Increasing evidence of a strong connection between sugar and cancer, MedicalXPress, March 20, 2019, https://medicalxpress.com/news/2019-03-evidence-strong-sugar-cancer.html
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