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Time To Stop Drinking Soda?

An interesting study found that high fructose corn syrup promotes the growth of intestinal tumors - in mice. The amount was fairly small - the equivalent of 12 oz of soda (with about 20 g of high fructose corn syrup) per day. The big question now: Is this also true for humans?

A number of studies find an association of soda consumption (which typically has high-fructose corn syrup in it), obesity,  and cancer (e.g. colorectal cancer) in humans, but the question remained whether this was due to obesity (obesity is linked to many types of cancer) or whether the high fructose corn syrup is directly contributing to tumor development or tumor growth. Based on the results of this study, the researchers felt that the high fructose corn syrup "enhances" or "promotes" intestinal tumor growth. Yikes.

From Science Daily: High-fructose corn syrup boosts intestinal tumor growth in mice

Does sugar directly feed cancers, boosting their growth? The answer seems to be 'Yes' at least in mice according to a study led by researchers at Baylor College of Medicine and Weill Cornell Medicine. 

Their study, published in Science, showed that consuming a daily modest amount of high-fructose corn syrup -- the equivalent of people drinking about 12 ounces of a sugar-sweetened beverage daily -- accelerates the growth of intestinal tumors in mouse models of the disease, independently of obesity. The team also discovered the mechanism by which the consumption of sugary drinks can directly feed cancer growth, suggesting potential novel therapeutic strategies.

"An increasing number of observational studies have raised awareness of the association between consuming sugary drinks, obesity and the risk of colorectal cancer," said co-corresponding author Dr. Jihye Yun, assistant professor of molecular and human genetics at Baylor. "The current thought is that sugar is harmful to our health mainly because consuming too much can lead to obesity. We know that obesity increases the risk of many types of cancer including colorectal cancer; however, we were uncertain whether a direct and causal link existed between sugar consumption and cancer. Therefore, I decided to address this important question when I was a postdoc in the Dr. Lewis Cantley lab at Weill Cornell Medicine."

First, Yun and her colleagues generated a mouse model of early-stage colon cancer where APC gene is deleted. "APC is a gatekeeper in colorectal cancer. Deleting this protein is like removing the brakes of a car. Without it, normal intestinal cells neither stop growing nor die, forming early stage tumors called polyps. More than 90 percent of colorectal cancer patients have this type of APC mutation," Yun said.

Using this mouse model of the disease, the team tested the effect of consuming sugar-sweetened water on tumor development. The sweetened water was 25 percent high-fructose corn syrup, which is the main sweetener of sugary drinks people consume. High-fructose corn syrup consists of glucose and fructose at a 45:55 ratio.

When the researchers provided the sugary drink in the water bottle for the APC-model mice to drink at their will, mice rapidly gained weight in a month. To prevent the mice from being obese and mimic humans' daily consumption of one can of soda, the researchers gave the mice a moderate amount of sugary water orally with a special syringe once a day. After two months, the APC-model mice receiving sugary water did not become obese, but developed tumors that were larger and of higher-grade than those in model mice treated with regular water.

"These results suggest that when the animals have early stage of tumors in the intestines -- which can occur in many young adult humans by chance and without notice -- consuming even modest amounts of high-fructose corn syrup in liquid form can boost tumor growth and progression independently of obesity," Yun said. "Further research is needed to translate these discovery to people; however, our findings in animal models suggest that chronic consumption of sugary drinks can shorten the time it takes cancer to develop. In humans, it usually takes 20 to 30 years for colorectal cancer to grow from early stage benign tumors to aggressive cancers."

The team then investigated the mechanism by which this sugar promoted tumor growth. They discovered that the APC-model mice receiving modest high-fructose corn syrup had high amounts of fructose in their colons. "We observed that sugary drinks increased the levels of fructose and glucose in the colon and blood, respectively and that tumors could efficiently take up both fructose and glucose via different routes."

"Most previous studies used either glucose or fructose alone to study the effect of sugar in animals or cell lines. We thought that this approach did not reflect how people actually consume sugary drinks because neither drinks nor foods have only glucose or fructose. They have both glucose and fructose together in similar amounts," Yun said. "Our findings suggest that the role of fructose in tumors is to enhance glucose's role of directing fatty acids synthesis. The resulting abundance of fatty acids can be potentially used by cancer cells to form cellular membranes and signaling molecules, to grow or to influence inflammation."

"This study revealed the surprising result that colorectal cancers utilize high-fructose corn syrup, the major ingredient in most sugary sodas and many other processed foods, as a fuel to increase rates of tumor growth," Cantley said. "While many studies have correlated increased rates of colorectal cancer with diet, this study shows a direct molecular mechanism for the correlation between consumption of sugar and colorectal cancer."

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