Does sugar cause cancer?

Does sugar feed cancer cells?

These are amongst the most frequently asked questions I receive in clinic. Many people believe that sugar causes or worsens a cancer diagnosis, and have often attempted to exclude sugar and/or carbohydrates from their diet in dramatic fashion. We can thank the lovely internet for providing an abundance of misinformation and fear mongering on this topic. 

My clients are often very relieved to learn that sugar is a necessary part of a healthy, well-balanced diet. Through education, improved planning, and addressing food anxieties, my clients inevitably develop a healthier relationship with ALL FOODS, including their beloved cakes and bickies. Sounds good, doesn’t it? Read on to learn more about how sugar metabolism works and why we need sugar and carbohydrates in our diet.

Understanding Sugar in Our Bodies – What is Sugar and How Does it Work?

When we think of sugar, images of white granules on a teaspoon or sweet desserts often come to mind. However, it's important to recognise that all sugars are just carbohydrates, packaged up differently. Let’s have a quick biology lesson. Simple sugars like table sugar are single chain carbohydrates ie. they contain only one or two units of sugar and are broken down very quickly by the body. On the other hand, long chains of sugar units are known as complex carbohydrates like grains and starchy vegetables. Think of sugar molecules as a chain. The shorter the chain, the quicker the links are broken down in the body, releasing sugar into the bloodstream ready for the cells to use as fuel. All carbohydrates, long or short, will eventually be broken down in the body to simple sugars like glucose, fructose or galactose, providing essential energy for the body. To put this in perspective, the oats and the lentils you eat will eventually become glucose, just like table sugar. We’ll circle back to this in a moment, because the speed at which sugars are broken down matters – this is something called the glycaemic index.

Some cells in the body, such as our brain cells and red blood cells, rely solely on glucose to function. Other cells can use alternative fuel sources too like protein and fat. When there's an inadequate amount of sugar floating around the body, our liver steps in, engaging in gluconeogenesis, a process of creating glucose. While this is a clever adaptation, it's not without drawbacks, potentially leading to the breakdown of muscle and fat stores to produce glucose.

Sugar serves as an efficient source of energy fuelling all cells in the body, including cancer cells. Cancer cells are hungry because they divide rapidly, and they will consume anything and everything. It’s important to focus on making sure the healthy cells in the body are properly fuelled to ensure they are well enough to combat cancer, to withstand cancer treatments and to promote recovery.

Remember, if cancer cells lack sugar as a fuel source, they will resort to utilising muscle and fat stores instead. Losing your muscle stores during cancer treatment raises significant concerns, as muscle wasting can result in a poorer prognosis, increased likelihood of side effects, and more frequent hospital admissions. Hence, it remains important to nourish our bodies with a variety of macronutrients, including carbohydrates and sugar.

The Lowdown on Low GI Carbohydrates

Remember our discussion on complex and simple carbohydrates before? The Glycaemic Index (GI) is a system that ranks carbs based on how quickly they raise blood glucose levels. Low GI carbohydrates (complex carbs) are those that break down slowly during digestion, resulting in a gradual increase in blood sugar levels, giving the pancreas time to produce enough insulin to help absorb the glucose into the cells to be used as energy. High GI carbohydrates are simple carbs which are broken down quickly, rushing into the blood stream resulting in a glucose spike. Having stable blood sugar levels contributes to overall health and helps to keep energy levels stable throughout the day.

Foods categorised as low GI include a variety of foods such as whole grains (like oats, barley, pasta and grainy bread), legumes (like lentils, chickpeas, and beans), and most fruit. These foods not only help in moderating blood sugar spikes but are also packed with fibre, vitamins, and minerals to support health. The table below shows some common low and high GI carbohydrates.

There is a growing body of evidence showing that a low GI diet is protective for breast cancer and may help to reduce the risk of recurrence. A high intake of sugar sweetened drinks like soft drinks and juice may increase the risk of breast cancer, indicating that high GI carbohydrates are not ideal in large amounts. Our bodies can handle a small to moderate amount of high sugar (high GI) foods, but when consumed in excess, they disrupt optimal body functioning and may increase the risk of cancer.

Moreover, it’s possible to reduce the glycaemic index of a meal or snack by adding healthy fats, protein, or vinegars. This might look like having nuts with your favourite slice of cake, adding avocado and chicken to a pasta salad, or a slice of cheese with your morning fruit can lower the GI of your meal.

It’s worth noting that during cancer treatment, when side effects are at their worst and consuming enough food is difficult, sugar plays a vital role in fuelling the body. Simple carbs like a lemonade or a serving of two-minute noodles might be all you can tolerate, and that’s perfectly okay. This helps to prevent muscle being broken to fuel the body. During treatment, eating enough takes precedence over maintaining a well-balanced diet.

The Bottom Line

We need carbs. Our bodies are designed to use carbohydrates to fuel our bodies. Cutting out sugar or carbohydrates will not selectively affect cancer cells, but will detrimentally affect all cells in the body. Low GI carbohydrates provide extra fibre, micronutrients and a slower release of sugars to help support better health, and are the preferred type of carbohydrates to consume.

The notion that ‘sugar feeds cancer’ is an oversimplification of a complex process. Sugar provides fuel for all cells, and we need to prioritise the wellbeing of our healthy cells. If we were to truly eliminate sugar, this would be mean giving up all sources of carbohydrate and eliminating whole food groups, which would only deprive our bodies of our preferred fuel source and leave us with a multitude of micronutrient deficiencies. This would only serve to weaken us physically and mentally, and is certainly not worth it in my book.

So ultimately, a diet for breast cancer should focus on including a wide variety of foods in the diet, including wholefoods, complex carbohydrates, protein and healthy fats. Allow freedom to enjoy your favourite foods too. There is a place for all foods.

Do you have more questions? Get started with the Confusion to Confidence e-Guide below!

Are you struggling to fuel your body well body during cancer treatment? Or maybe you are feeling worried about what to eat after a cancer diagnosis?

Jump on a FREE Discovery Call with Oncology Dietitian Alex Salmon to start your journey towards feeling better.