Can sugar cause cancer? Separating fact from fiction

Since the 1920s, sugar overconsumption (or carbohydrate toxicity) had already been seen as a key risk factor for the development of diabetes.

What about cancer? We often hear sugar blamed for cancer, but the reality is more complex. It’s a fact that our bodies rely on sugar (glucose) for energy, coming from various sources:

Simple sugars: Glucose, fructose (found in fruits)

Complex sugars (carbohydrates): Starches in cereals (rice, bread, pasta), and potatoes.

Complex sugars break down into simple sugars for our cells to use. This applies even to non-sweet foods, made of carbohydrates.

Fueling every cell: The importance of glucose

Every cell type, from muscles to nerves, needs glucose for survival. They obtain energy through a process called glycolysis – breaking down glucose.

Sugar and cancer: Fact vs myth 

Cancer cells are fast-growing and require a lot of glucose. This misconception led to the myth that cutting sugar starves cancer.

Unfortunately:

We can’t direct glucose only to healthy cells.

Cancer cells also need other nutrients like amino acids and fats.

Warburg effect: What you need to know

It was 100 years ago when German scientist Otto Warburg (who was also a Nobel laureate) observed the fact that cancer cells eat a lot more sugar than normal cells. This is known as the "Warburg Effect".

In a nutshell, the "Warburg Effect" says that normal cells can stop after eating one piece of candy. But cancer cells can't stop eating candy. This phenomenon is called "aerobic glycolysis for energy production".

The use of the Warburg effect for cancer diagnosis is a scientific breakthrough. Since cancer cells gobble up sugar more than healthy cells, doctors inject a special sugar tracer (known as fluorodeoxyglucose, or FDG).

This method is so efficient that it can also be used with other scans (CT scans) for better detail and to monitor treatment effectiveness. This is just one tool, though not a perfect test, and doctors use it with other methods for diagnosis.

Yet science is a slow and systematic process of observation and experimentation. There’s no direct evidence that a sugar-free diet prevents or aids cancer treatment.

In fact, severely restricted diets can be detrimental for:

Fiber and vitamins: Lack of these nutrients from eliminated healthy foods can harm overall health.

Cancer patients: Treatment can cause weight loss and stress, making restrictive diets dangerous.

2 studies on sugar and cancer risk

While no study has found that sugar directly causes cancer, there are at least two that found direct links between sugary food intake and certain types of cancer – specifically liver cancer and proximal colon cancer.

However, it's a medical fact that high sugar intake is a key contributor to weight gain – a significant risk factor for several cancers. CDC has identified elevated risks of 13 types of cancers that come with obesity and being overweight.

Two studies, however, currently stand out showing a strong link between high sugar consumption and cancer risk:

Study #1

Research published on August 8, 2023 in JAMA Network led by a team from Harvard suggests high sugar-sweetened beverage consumption (1+ servings daily) may increase liver cancer and chronic liver disease death risk in postmenopausal women. They analysed data from nearly 99,000 women followed for 20 years.

Those consuming the most sugary drinks had an 85 per cent higher liver cancer risk (18.0 vs 10.3 per 100,000 person-years) and a 150 per cent higher risk of death (17.7 vs 7.1 per 100,000 person-years) from chronic liver disease compared to those consuming few sugary drinks. Artificially sweetened beverages, however, didn't show a similar association.

Study #2

An earlier study, published in 2022 in the American Journal of Clinical Nutrition, conducted by researchers at the Department of Medical Oncology, Dana-Farber Cancer Institute and Harvard Medical School followed 121,111 people to see if sugary drinks (SSBs) and fructose were linked to colon cancer.

What they found: People who drank more sugary drinks were more likely to get proximal colon cancer (the first part of the colon) specifically. This risk increased the more sugary drinks they consumed. Those who ate more fructose also had a higher chance of getting this type of colon cancer.

A new hope: Targeting cancer's energy metabolism

While sugar reduction doesn't treat cancer directly, research is exploring how cancer cells use energy differently:

Cancer cells, following the Warburg effect, often bypass energy production in mitochondria (cellular “batteries”) and use a less efficient process.

This "weakness" could lead to new cancer treatments:

However, these approaches are still experimental, and their safety and effectiveness remain under investigation. Restricting your diet during treatment is not recommended.

The indirect link: Sugar and weight gain

Though sugar (sweet carbohydrate) doesn't directly cause cancer, there's an indirect link:

High sugar intake and weight gain: Over time, sugary foods can lead to weight gain.

Obesity and cancer risk: Being overweight or obese increases the risk of 13 types of cancer.

According to the US CDC, being overweight or having obesity are linked with a higher risk of getting 13 types of cancer, which make up 40 per cent of all cancers diagnosed each year.

While being overweight or having obesity doesn’t mean that someone will most definitely get cancer, it does mean that they are more likely to get cancer than if they kept a healthy weight.

[Note: Many things are associated with cancer, but avoiding tobacco use and keeping a healthy weight are two of the most important steps you can take to lower your risk of getting cancer.]

Reducing sugar: Small steps, big impact

While sugar itself doesn’t cause cancer, limiting sugar intake is still important for weight management and overall health.

Here's how:

Focus on “free sugars”: These are added sugars in processed foods, drinks (sodas, energy drinks), juices, syrups, and some breakfast cereals, ready meals, pasta sauces, and yogurts.

Read food labels: Check the ingredients list and sugar content to choose lower-sugar options.

Limit sugary drinks: They are a major source of sugar and offer no nutritional benefits.

Cut back on sweets and treats: Enjoy them occasionally, but limit their presence in your diet.

A healthier you

Cancer is a complex disease with various contributing factors.

So it's not as straightforward as saying "candy causing tumours", as all cells, including cancer cells, use glucose for energy. Cancer cells, however, do require loads more sugar than regular, healthier cells. 

High sugar intake may increase cancer risk: Studies suggest a link between high sugar intake and a higher risk of certain cancers. However, it's likely a complex interplay with factors like weight gain and chronic inflammation.

Individual choices: We can make informed decisions by checking labels and limiting sugary options.

Government policies: Measures like better food labeling, sugar tax and promoting healthy options could help make healthier choices easier.

Focus on overall diet and healthy habits: Restricting sugar alone might not be the solution. Limiting added sugars, exercising regularly, and eating a balanced diet is crucial for overall health and reducing cancer risk.

A balanced approach is key.

[Note: This information is intended for general knowledge only and does not constitute medical advice. Please consult with a healthcare professional for personalised recommendations.]