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Does sugar cause cancer?

Dr See Hui Ti from Parkway Cancer Centre answers some commonly-asked questions on the link between sugar and cancer.

What is sugar?

Sugar is a generic name for sweet-tasting, soluble carbohydrates, many of which are used in food. There are two types of sugars: Simple sugars (monosaccharides), which include glucose, fructose, and galactose; and compound sugars (disaccharides or double sugars), which contain two molecules of sugar joined together.

Common examples of compound sugars are sucrose (glucose + fructose), lactose (glucose + galactose), and maltose (glucose + glucose). Compound sugars are broken down into simple sugars before they are absorbed into the bloodstream in the body.

Simple sugars are naturally found in many foods, from fruits and vegetables to dairy products. They can also be added to foods and beverages such as candies, sugar-sweetened fruit drinks and soft drinks.

Table sugar, or sucrose, is the most common example of compound sugar.

Why do we need sugar?

We do not need sugar. What we need are carbohydrates or carbs, the main source of macronutrient that provides energy for the body. Besides carbs, the other two macronutrients are fat and protein.

Carbs are commonly found in fruits, dairy products, rice, noodles, bread, and starchy vegetables (e.g. potatoes, corn and tapioca), and also sugar-sweetened desserts and drinks. They are broken down into simple glucose, to be burned as energy and to generate ATP (Adenosine triphosphate) for the body.

ATP is an energy-carrying molecule that stores and releases energy as required by the body cells.

What is the link between sugar and cancer?

Cancer is a term given to a group of diseases characterised by the uncontrollable division of abnormal cells in the body with the potential to invade or spread to other parts of the body.

There are more than 100 types of cancer that affect almost every part of the body, such as breast cancer, lung cancer, colorectal cancer, skin cancer, cervical cancer, prostate cancer, and lymphoma.

There are no conclusive studies on human subjects to suggest that sugar causes cancer or encourages cancer cells to grow faster.

All cells, including cancer cells, need blood sugar for energy. Giving more sugar to cancer cells doesn’t speed their growth. Nor does depriving cancer cells of sugar slow their growth. A cancerous tumour that has not spread will not spread because of sugar. However, some research has shown that cancer cells do consume more sugar (glucose) compared to normal cells.

Still, there is no need to completely cut off the supply of sugar from our diet. The human body requires sugars to function; starving it of energy will only cause the body to weaken.

What we should avoid, however, is the excessive intake of sugar. Too much sugar that is not used up by the body can lead to an increase in blood sugar and hyper-insulinaemia (excessive production of insulin). This causes inflammatory responses in our bodies that may lead to an increased risk of cancer.

A high-sugar diet may also contribute to diabetes and obesity, which have been linked to an increased risk of developing various types of cancer.

Is there any link between sugary drinks and cancer?

While research on sugary drinks and the risk of cancer is still limited, a study published by The British Medical Journal in 2019 adds to existing evidence of a link between higher consumption of sugary drinks and an increased risk of some cancers.

In this study, a team of researchers in France surveyed more than 100,000 adults with an average of age of 42; 79 per cent of whom were women. The participants completed at least two 24-hour online validated dietary questionnaires that calculated their daily intake of sugary drinks (sugar-sweetened beverages and 100 per cent fruit juices) and artificially sweetened (diet) beverages, and followed up with them for up to nine years.

The study found that just a 100 ml increase of sugary drinks per day was associated with an 18 per cent increased risk of cancer, and a 22 per cent increase in breast cancer. This association was seen for the intake of both sugar-sweetened drinks and fruit juices, while the intake of artificially sweetened (diet) beverages was not associated with an increased risk of cancer.

Other well-known risk factors for cancer, such as age, gender, family history, smoking habits and physical activity levels, were also taken into account.

What is your advice to cancer patients?

There is no need to ban sugar completely from the diet. Eat everything in moderation, but consume sugar minimally. Focus on eating well with a varied and balanced diet, e.g. eat complex carbs to fuel the body or take higher plant-based foods. Fibre and slow-releasing carbs can reduce cancer risks and provide nutrition for a stronger body. Besides good nutrition, keep active physically.