Ask the Dietitian: What’s the Real Connection Between Sugar and Cancer? 

Removing sugar from your diet won’t ‘starve’ cancer. But research suggests cutting back on sugar may be a good idea.

If you’ve been told to cut out sugar because it “feeds” cancer, you’re not alone.

The research on sugar and cancer is compelling.

For about a century, researchers have known that cancer cells use glucose as their main source of energy. Research in mice has found that restricting glucose intake may help chemotherapy work better, slow cancer growth, and increase chances of survival.

Maybe you’ve also heard the buzz that ketogenic diets — which cut out sugar — have had promising anti-tumor effects in some people.

In reality, the connection between food and cancer is not that straightforward, and more research is needed. Here’s what we do know:

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Does sugar cause cancer?

We don’t know for sure. Sugar’s role in the development of cancer is controversial.

In humans, we can only look at observational studies. Research from 2022 suggests that a high sugar intake is strongly linked to the development of cancer and its progression — including breast cancer.

The results in mouse studies are convincing. For example, in that study, the researchers explain how mice fed high sucrose or high fructose diets developed various types of cancer earlier and more often and had more cancerous cells in total than mice in the control groups.

Many studies on the effects of added sugar consumption examine people who consume a “standard American diet,” which is filled with processed foods and added sugar instead of vegetables, fruits, nuts, and other nutrient-dense foods.

“Added sugar” refers to sugar that’s incorporated into processed foods and includes sweeteners like corn syrup and table sugar.

The 2022 research review found that eating large amounts of sugar every week was linked with an increased risk of certain cancers, including breast cancer, colorectal cancer, and pancreatic cancer.

The researchers identified a few ways that sugar triggers inflammation, which earlier research from 2019 suggests is strongly linked with cancer development.

A 2020 study with over 100,000 participants found that high total sugar intake was associated with a 17% higher risk of overall cancer and a 51% higher risk of breast cancer.

Diets high in added sugar have also been linked with an increased risk of:

• heart disease
• depression
• fatty liver disease
• type 2 diabetes

It’s not just added sugars that may be harmful. A high intake of natural sugars — like the sugar in fruit juice — has also been associated with an increased risk of cancer.

Keto diets may have anti-tumor effects

Some scientists have hailed ketogenic diets as a potential way to induce anti-tumor effects in people with cancer.

In ketogenic diets, you stop eating added sugars completely and strictly limit your carbohydrate intake. You do this while increasing your consumption of fats and eating typical amounts of protein.

This induces lower levels of glucose in your bloodstream. Your cells can adapt to this, but cancer cells have a tougher time.

Some researchers have proposed ketogenic diets as a potential complementary therapy for cancer, but clinical study results are mixed.

A 2022 research review found that ketogenic diets have had an anti-tumor effect in some cancer patients, while others found they had no effect at all.

The effects of ketogenic diets also appear to depend on the type of cancer.

So, while ketogenic diets may have an anti-tumor effect in some cases, they may not always help. More research on their effects and safety in people is needed.

Let’s put this in context

It’s important to understand that your diet as a whole is what matters most when it comes to disease prevention.

A diet filled with ultra-processed foods and added sugars has been associated with an increased risk of many health conditions, including heart disease and cancer.

The same is true in reverse: Diets filled with nutrient-dense food like vegetables, nuts, and fish are associated with a prolonged life and reduced risk of health issues.

Occasionally enjoying your favorite sweet treat is not dangerous and won’t put your health at risk if the majority of your diet is made up of whole foods.

If you want to cut back on sugar

The American Heart Association recommends limiting sugars to 6% of your daily calories. That’s about 6 teaspoons for women and 9 teaspoons for men.

Keep in mind that many popular foods and drinks contain multiple teaspoons of added sugar per serving. For example, a 12-ounce can of Coke contains 39 grams of added sugar, which is nearly 10 teaspoons. So just one can of soda can put you over the recommended amount.

Here’s how you can cut back on the sweet stuff:

• Replace soda, energy drinks, fruit juices, and sweetened teas with water or unsweetened seltzer. If you don’t enjoy the taste of plain water, try adding a squeeze of lemon or lime.
• If you normally order sweetened coffee drinks, try cutting the sweetener in half or choose a natural sugar alternative like monk fruit instead of sweetened syrup or table sugar.
• Opt for plain, unsweetened yogurt instead of flavored yogurt. You can use fresh or frozen berries to add natural sweetness.
• Buy salad dressings, marinades, pasta sauces, nut butters, ketchup, and other condiments made without added sugars.
• Replace sugary breakfast cereals with a more filling option, like a veggie omelet and a side of fruit. Or plain oats topped with Greek yogurt, berries, and nut butter.
• If you eat dessert every night, you may try slowly cutting back. You can start by eating dessert every other night and decrease your intake from there. You can also replace your treat with a lower sugar option, like homemade peanut butter, chocolate “nice cream,” or chocolate-covered almonds.

The bottom line

You don’t need to overhaul your diet overnight. At the end of the day, it’s important to focus on your diet as a whole.

You can start by focusing on one piece of your diet that you feel needs the most work. For example, if your current breakfast is a pastry and coffee with sugary syrup, try swapping it for eggs with a side of fruit and coffee with monk fruit sweetener.

Working with a healthcare professional like a registered dietitian can also help you get started.

You can find recommendations and share your own low sugar swaps in the Bezzy BC community forums.