Obesity is known to increase the risk of developing cancer, including colorectal cancer. Now, a new study published on 22 March in Science suggests high-fructose corn syrup, a sweetener used in many soft drinks, might actually speed up tumour growth in the colon, independent of obesity. Drinking large amounts of sugary drinks leads to obesity, but can soft drinks increase cancer growth in non-obese people?
The researchers, led by Dr Jihye Yun, an assistant professor of molecular and human genetics at Baylor University in the US, first created a mouse model of early-stage colon cancer by deleting the Adenomatous polyposis coli (APC) gene ― around 80 per cent of human colon tumours are linked to a mutations in the APC gene (2). WIthout the APC gene, colorectal cells don’t know when to stop growing, leading to the formation of a polyp or early-stage tumour.
Then, they fed the genetically modified mice sugar-sweetened water ― containing 25 per cent high-fructose corn syrup composed of both glucose and fructose ― to see how it would affect tumour growth. Mice permitted to freely consume the sugary drink rapidly gained weight within one month. Whereas, those fed only around one-tenth of a teaspoon a day ― equivalent to one can of soda ― did not gain weight. But interestingly, there was no difference in the development of tumours between the sugar drinking mice and control mice (water only). However, after two months, tumours in the sugar-fed mice had become larger and more invasive.
In other words, mice consuming a modest amount of high-fructose corn syrup daily ― around 400 mL of a sugary drink ― showed accelerated intestinal tumour growth, independent of obesity. Therefore, consuming even relatively small amounts of high-fructose corn syrup in drinks can boost tumour growth. Typically, colorectal cancer takes 2–3 decades to develop from an early stage polyp into aggressive cancer. But these findings suggest that consuming sugary drinks could accelerate this quite considerably.
So, why does this happen? The authors report increased the concentrations of fructose in the colons the sugar-swigging mice. Whereas glucose can be efficiently removed by intestinal cells, the removal of fructose is more passive, which allows it to build up in the colon and remain available to the tumour. The sugar is then “trapped” by the tumour, and once inside the cancerous tissue, fructose is broken down by an enzyme called fructokinase (KHK) or converted into fatty acids to support the tumour’s growth.
The findings still need to be demonstrated in humans, but they highlight the potentially harmful effects of sugary drinks. In particular, a direct causal link between consuming high-fructose corn syrup-sweetened drinks ― even in relatively small quantities ― and accelerated tumour growth.
Next, the team hopes to test whether intestinal polyp growth can be slowed in humans by eating a low-sugar diet. They are also considering the possibility of using a KHK-inhibiting drug, currently being tested in clinical trials for fatty liver disease, to treat colon cancer. For now, the best advice may just be to avoid sugary drinks.
(1) Goncalves, M.D. et al. High-fructose corn syrup enhances intestinal tumor growth in mice. Science (2019). DOI: 10.1126/science.aat8515
(2) Fearnhead, N.S., Britton, M.P., and Bodmer, W.F. The ABC of APC. Human Molecular Genetics (2001). DOI: 10.1093/hmg/10.7.721