What to know about the connection between sugar and cancer
I became interested in sugar and how it’s impacted the obesity epidemic when I worked on the documentary Fed Up in 2014. Through my Stand Up To Cancer work, I met Dr. Lewis Cantley, director of the Sandra and Edward Meyer Foundation at Weill Cornell. He’s been studying how sugar feeds cancer cells… yet another reason why you or anyone you know who’s dealing with cancer may want to stay away from the sweet stuff. Here’s our important conversation.
Katie Couric: How long have you been studying the impact of sugar on cancer?
Dr. Lewis Cantley: The observation that cancers consume much more sugar than normal tissues was discovered by a German Nobel Laureate named Otto Warburg about 100 years ago. When I was a graduate student at Cornell in the 1970s, much of cancer research centered around why cancer cells eat so much more sugar than normal cells.
I also started my own lab at Harvard in the late 1970s, and I was interested in how insulin tells cells to take up the sugar glucose. It had been known since the 1920s that insulin is a hormone made in the pancreas that causes muscle to take up glucose from the blood, and that diabetes was a consequence of either a failure of the pancreas to make insulin (Type 1 diabetes) or a failure of muscle or liver to respond to insulin (Type 2 diabetes). Yet, in the 1970s we had no idea how insulin worked in these tissues.
It was in the course of doing this research that my laboratory discovered a gene that mediates glucose uptake into both normal cells (fat and muscle) and cancer cells. We now know that the gene, called PIK3CA, is among the most frequently mutated genes in human cancers. These mutations explain why cancers take up glucose and use it to grow.
Can you describe to the average person what you’re learning in your research?
The first thing we have learned is that there is a link between insulin and cancer. Insulin stimulates a protein in that gene, making it be more efficiently activated by insulin — and this drives many cancers, including endometrial, breast and colorectal cancers. This may explain why people who eat a lot of sugar, which causes an elevation in insulin in the blood, are at a higher risk for many cancers. Insulin resistance, which is caused by eating too much sugar, also causes an increase in insulin levels in the blood and this disease also correlates with increased risk of some cancers.
When you talk about sugar — are we talking about high fructose corn syrup, natural sugar, regular table sugar, and sugar-sweetened beverages?
Although there are many types of sugars (galactose and lactose in milk, maltose in grains, sucrose/table sugar from sugar cane or sugar beets and high fructose corn syrup from chemically converted corn starch), it is the latter two that are the sweetest and are most frequently found in our drinks and desserts.
Both table sugar and high fructose corn syrup are a mixture of glucose and fructose. It is the fructose that provides most of the sweet flavor. Fruits that taste sweet also have a mixture of glucose and fructose, though as I will explain, they are not as dangerous as fruit juices or drinks with sucrose or high fructose corn syrup added — in regard to risk for obesity, insulin resistance, diabetes, and cancer.
What about sugar substitutes like Equal and Splenda? Should we be worried about those?
Sugar substitutes are not as dangerous as sugary drinks, in that they do not acutely raise serum glucose levels. However, they can raise serum insulin levels and they drive the desire for more sweet foods and maintain the addiction to sugar. In general, using sugar substitutes causes a craving for desserts, making it difficult to lose weight.
Is it true that sugar can feed cancer cells and make them grow faster?
Without a doubt, most cancers use sugar glucose to grow. That’s why physicians can find cancers by monitoring where radioactive glucose accumulates in our bodies with FDG-PET scans. What makes these cancers take up glucose and use it to grow are mutations in genes like PIK3CA, and in many cases these mutations allow insulin to drive tumor growth.
So eating sugar is a double danger in regard to cancer. It increases the amount of glucose available to the tumor, but it also increases the level of insulin in the bloodstream.
Are you studying a particular cancer — or is your research applicable to all cancers?
Over the years, my laboratory has studied many types of cancers, including breast, endometrial, ovarian, brain, lung, pancreatic, prostate, colorectal and blood cancers. All of these cancers can potentially utilize insulin to drive glucose-dependent tumor growth.
However, colorectal cancer is unique in how it responds to sugars. Since these cancers grow in the colon, they can directly eat the sugar fructose before it gets into the bloodstream. We recently showed that, in mice genetically engineered to have colon polyps, the polyps grow two to three times faster if the mice are fed sugary drinks — that are the mouse equivalent of a 12-ounce sugary drink containing sucrose or high fructose corn syrup. In contrast, if the same amount of sugar is eaten as a whole apple or whole orange, the sugar is absorbed into the bloodstream during the slow movement of solid food through the intestine during digestion. So the fructose can feed the colon polyps if consumed in liquid form, but not if consumed as a solid fruit.
Do you eat sugar? And do you think people should avoid all sugar as a way to prevent cancer?
I eat fruits but do not drink fruit juice or any other drink with added sugar or artificial sweeteners. Dry wines have less sugar than fruit juices, so moderate consumption of dry wines is less likely to raise the level of blood glucose and insulin than fruit juices. I skip dessert completely. In essence, I eat what my great grandparents ate in the days when sugar was the most expensive food available in rural West Virginia.
This interview has been lightly edited and condensed.
This originally appeared on Medium.com