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Many of us enjoy soda without a second thought.

About two-thirds of children and teenagers and half of adults in the United States regularly consume sugary drinks, according to the Centers for Disease Control and Prevention (CDC). 

And while Jihye Yun, Ph.D., prefers green tea, she spends plenty of time thinking about soda. The Yun Laboratory’s research explores how diet affects the intestine, with one project aiming to understand how sugary drinks can impact colorectal cancer development.

Ahead, she shares more about her research into sugary beverages, including how we can apply these findings to our own diets. 

Can sugary drinks cause colorectal cancer?

Yun started her research with an intriguing question: We already know sugary drinks can cause cancer if they lead to high body weight, but could sugary drinks cause cancer directly? While the common belief was that sugary drinks weren’t directly harmful beyond their calorie content, Yun had her doubts.

Her interest in the topic felt particularly urgent due to a noticeable rise in colorectal cancer among young adults over the last four decades. She wondered if this increase coincided with the growing fondness for sweetened beverages.

“The rise in early-onset colorectal cancer likely isn’t from genetic changes, as these usually take much longer than four decades to appear,” Yun explained. “It’s probably from environmental factors, and I’m really curious about our diets, especially our increased sugar intake.” 

Driven by this possibility, Yun embarked on a mission to find out if there was more to the story.

Yun's team used laboratory models to explore whether consuming beverages sweetened with high-fructose corn syrup, a common sweetener that contains glucose and fructose, leads to tumor growth. 

The model used in Yun’s study was prone to developing intestinal polyps, which are tissue growths that can eventually turn into cancer over time. This model allowed research to be conducted in months rather than years.

The findings were striking, Yun says. Consuming the equivalent of just one can of soda sweetened with high-fructose corn syrup per day led to the development of more and larger tumors, even though it didn’t affect weight. 

"Before we conducted this study, people didn’t believe that sugar itself was harmful in terms of cancer. They thought that eating too much sugar, which can lead to weight gain or obesity, was the main issue," she says. “Our results proved that sugary drinks can directly cause cancer by increasing the number, size and severity of tumors in laboratory models.”

These findings were an important first step in figuring out if sugary drinks impact colorectal cancer risk in humans. Using lab models, Yun’s team was able to show how and why this cancer risk occurred. After their work was published, additional studies in humans found links between sugary drinks and colorectal cancer risk.

“Human epidemiology studies only provide the correlation, but not causality and not mechanism. That is the reason that our studies using lab models are important,” she says.

Why do sugary drinks impact colorectal cancer risk? 

Another critical aspect of Yun’s research focuses on understanding why sugary drinks might increase the risk of colorectal cancer beyond being linked to weight gain and obesity. Here’s how Yun explains the potential impact.

Sugary drinks and the colon

When the small intestine can't fully absorb the amount of sugar consumed, that sugar spills over into the large intestine and colon. According to Yun, the glucose and fructose from high-fructose corn syrup can boost tumor growth in two ways: glucose is absorbed by blood vessels, while fructose is absorbed directly in the colon. Tumor cells in the colon typically have many transporters for these sugars. Once inside the tumor cells, the combination of glucose and fructose stimulates a process called lipid synthesis, which in turn contributes to tumor cell growth.

Other potential effects

Yun’s team is also investigating whether diet can influence colon cancer development by altering the gut microbiome. Yun describes the gut microbiome as a vast community of microorganisms, including bacteria, viruses and fungi, that live in our digestive systems. Generally, a diverse range of bacteria indicates a healthier microbiome. However, Yun's research suggests that sugar consumption is linked to a decrease in this microbial diversity.

The gut also acts as a barrier between what we consume and our bloodstream. Yun notes that sugar can weaken this gut barrier, allowing microbes to enter our bloodstream and increase inflammation. This heightened inflammatory state can make it easier for tumors to start forming or to grow further. 

What should we know about other sweeteners?

While Yun’s research has largely focused on high-fructose corn syrup, she often receives questions about the many types of sugars. 

Cane sugar (sucrose)

Yun advises being equally cautious with drinks sweetened with sucrose, or table sugar, which is made from sugar cane or sugar beets. She explains that sucrose is simply glucose and fructose bonded together. This bond is broken during digestion in our bodies. 

“It will become glucose and fructose at a one-to-one ratio in our body. So, it’s basically the same as high-fructose corn syrup,” she says. “We shouldn’t be fooled by food companies' claims that products with sucrose from sugar cane are healthier than products with high-fructose corn syrup. Both are essentially the same and equally harmful in our bodies.”

Sugars in honey or fruits 

Another question Yun regularly addresses is whether it is okay to consume honey or fruits.

She explains that while honey and fruits also contain glucose and fructose, like high-fructose corn syrup or sucrose, they also offer various micronutrients. The key is to consume them in moderation. 

“It's better not to consume large portions of honey or fruits at once, but a small amount is fine,” she advises.

Yun also suggests eating whole fruit instead of drinking fruit juice. This is because fruit juice doesn’t contain as much fiber as whole fruit. It also has high levels of sugars in liquid form, which Yun says could have similar harmful effects to sugary drinks. 

Artificial sweeteners

Aspartame, sucralose, saccharin... the list goes on. Yun often hears questions about whether artificial sweeteners are safe and their impact on health and cancer risk. 

While she notes a rapid increase in consumption of these artificial sweeteners after people began recognizing the harmful effects of high-fructose corn syrup and sucrose, she says there is still much we don't know about the health benefits and risks of these substances.

“The jury is still out on artificial sweeteners,” she says. 

Until there’s more conclusive research, Yun suggests avoiding or limiting artificially sweetened drinks when possible.

What about foods with high-fructose corn syrup or sucrose? 

High-fructose corn syrup or sucrose is used to sweeten more than just beverages. In fact, high-fructose corn syrup can be found in foods such as cereals, sauces, candies and more. 

Prior to her research, Yun says foods with sugars and sugary drinks were often researched together. This could lead to mixed results in human studies. 

Yun wanted to study sugary beverages independently because highly sugar-concentrated beverages can be quickly absorbed by the body and rapidly increase the body’s levels of fructose and glucose compared to the sugars in solid foods.

“Sugary drinks are unique. They are very highly concentrated; there's nothing except pure added sugar and water, and they can be absorbed quickly, increasing the levels of sugars in our bodies, which can be used by tumor cells and increase bad microbes,” she says. 

For your health, it is best to limit the amount of added sugar in your diet — regardless of whether you are drinking it or eating it in foods. MD Anderson recommends that men limit themselves to 36 grams of added sugar a day, while women should limit themselves to 25 grams.

MD Anderson dietitians also recommend choosing healthy foods and building in regular physical activity because following an overall healthy lifestyle is proven to help reduce your cancer risk. 

How should we proceed when it comes to sugary drinks? 

Yun has noticed a funny phenomenon when she presents her work at conferences. Before her presentations, she observes many peers drinking soda and other sugary beverages. However, after she presents, it's a different story.

For Yun, this reassures her of the impact of her team's work. By continuing to share her research, she hopes to encourage others to make healthier choices. 

“In my opinion, the most efficient way to remove the root cause of many chronic diseases, including cancer, is to avoid consuming sugary drinks,” she says, noting that this includes sodas, energy drinks and fruit juice with added sugar.

But even if you don’t want to cut out soda completely, Yun shares these tips for navigating your relationship with sugary beverages going forward. 

Determine whether soda is a treat or a habit.

Drinking sugary drinks regularly over a long period poses the greatest health risk. So, while Yun says that having a soda on occasion is OK, try not to make it a habit. 

“If you can control yourself, it’s fine to have these drinks occasionally, but remember that sugars are highly addictive,” she says.

Thinking about when you normally crave soda or energy drinks can help you plan for other options. For example, Yun used to be tempted to drink soda whenever she was eating greasy foods like pizza or hamburgers. These options left her feeling bad, so she cut back. 

While she says it can be challenging to break habits at first, it gets easier over time.

“The desire disappears if you stop,” she says. 

Read nutrition labels

Checking the nutrition label on your favorite beverage is an easy way to learn more about exactly what you’re consuming. 

If your drink doesn’t have a nutrition label or you see unfamiliar ingredients, Yun recommends doing a quick online search. This can be a helpful way to learn about ingredients, added sugar and the amount and types of carbohydrates in your drink.

She also suggests taking a closer look at the nutrition labels of energy drinks or concentrated juices that advertise health benefits like added protein or nutrients. 

“What they don’t show in their advertisement is that they have exactly the same amount, or even higher amounts, of added sugar, such as high-fructose corn syrup or sucrose, compared to soda,” she says.

Yun also strongly recommends that adults avoid giving sugary drinks to kids. Instead, she encourages adults to teach children about nutrition labels and other ways to be conscientious about what they eat and drink. 

Find new ways to hydrate

Instead of choosing sugary drinks, opt for water or other non-sweetened or naturally sweetened options. 

Adding fruits and vegetables to your water can be an easy way to add flavor without added sugar.

When she is in the mood for a refreshing drink, Yun likes to squeeze lemon juice into a glass of ice water and sweeten it with a few drops of honey. 

“It makes me feel good,” she says. “It’s nutritious, too.”

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