Oncology NutritionPreventative nutrition and health

Bittersweet – does sugar feed cancer?

What exactly do you mean by sugar?

When we think of sugar, most will think of white grains in a bowl or on a teaspoon. The term ‘sugar’ can be used for a range of molecules shown in the image below. Scientifically speaking, all sugars are carbohydrates; simple sugars are the links in a carbohydrate chain. The white stuff in the bowl is the disaccharide sucrose. All carbohydrates from food, whether from a cookie, milk or a carrot, will eventually be broken down by our digestive systems to release glucose, fructose and/or galactose.

Carbohydrates can be classified, in simple terms, to 3 main groups. Monosaccharides are single sugar units, disaccharides are 2 units joined together and polysaccharides are more complex carbohydrates made up of many sugar units.

Carbohydrate containing foods
  • Grains, breads, cereals
  • Pasta, rice, noodles
  • Fruit
  • Vegetables
  • Dairy products
  • Legumes and pulses (such as chickpeas, kidney beans, lentils, peas)
  • Nuts and seeds
  • Honey, syrups
  • Malt, beer
  • Sweets, biscuits, cake, pastries, ice cream, lollies, cordial, juice, soft drinks, cordial

Sugar feeds everything

Carbohydrates, particularly in the form of glucose, are our body’s preferred fuel source. Some cells – red blood cells and cells in our brains – use glucose almost exclusively. Our bodies like carbs so much that if we don’t have carbohydrates coming in from our diet, we have very sophisticated pathways that can generate glucose from other substrates (including amino acids and lactate in a process known as gluconeogenesis).

What this means is that if there is an insufficient energy supply coming in from carbohydrates, our bodies will switch to breaking down fat and muscle stores for fuel. In someone undergoing cancer treatment, protein is the preferred source of fuel. This can lead to weight loss, muscle wasting and malnutrition. And it doesn’t slow the cancer growth.

Cancer cells are greedy. They divide rapidly and grow faster than most healthy cells. This means they require and use more nutrients to grow than the healthy cells that are dividing at a regular rate.

Simple sugars fuel our bodies in a very efficient way. Combine this with the fact that cancer cells are greedy, and it’s no surprise that sugar fuels cancer cells more efficiently than our healthy cells. Anyone who’s had a PET scan explained to them will know that oncologists can use this phenomenon to assess for the presence and spread of cancer. It’s no wonder people ask the question if avoiding sugar would hinder cancer growth. We wish it were that simple.

Cancer cells are greedy

Cancer cells are experts at thriving. Yep. Cancer sucks.

Anyone who’s asked me this sugar question would have undoubtedly endured one of my drawings. What I would have attempted to draw (with much enthusiasm but quite poor artistic execution) is something a little like this…

Angiogenesis is a process of new blood vessels forming from pre-existing vessels.  Image source: National Cancer Institute.


You’ll see in the picture above the increased blood supply in the second image. Angiogenesis is a process of new blood vessels forming from pre-existing vessels. This phenomenon is seen in cancer cells as a means of increasing their supply of nutrients, oxygen and other factors to enhance their growth. Angiogenesis enables cancer cells to thrive more so than healthy cells. Us oncology clinicians hate it. And some very clever medical scientists have developed many anti-angiogenesis therapies (such as bevacizumab (Avastin®)) to use in cancer treatment.

What this means is that even if there is minimal energy and nutrients available within the body, there is more of a chance it will make it to cancer cells than healthy tissue.

Denying your body of carbohydrate foods is likely to have more of an impact on your healthy cells than it will on the cancer. With our brain and our blood cells relying on glucose for fuel, you can imagine the impact on energy levels, mood and performance.

Cancer feeds off everything

Cancer likes carbs. But what many Dr Google’s neglect to mention is that cancer cells will also use protein and fat for fuel in the absence of sugar. This includes your body protein (muscle) and fat stores.

If cancer cells, with their superior nutrient supply, can no longer source sugar from our body, they start to break down our muscle and fat stores for fuel. This means unintentional weight loss. Not good. During cancer treatment and recovery this means muscle wasting. Even worse.

So what do we do?

It’s been proposed that the growth of cancer cells may be slowed by starving them of sugar. The problem with that is there’s currently no method of cutting off the supply to cancer cells while keeping it open to normal cells.

Our best suggestion is to ensure the following:

  1. You’re eating enough quality protein foods to help preserve you lean body mass
  2. Include low glycaemic index carbohydrates in serves about the size of your fist at meals. Fuel your body and your mind.
  3. Include plant-based fats from nuts, seeds, avocado, extra-virgin olive oil and fish oils. Love Nemo. Be liberal with these if you’re losing weight.
  4. Reach your vitamin, mineral and phytonutrient requirements from a variety of foods, negating the need for supplements.
  5. Keep well-hydrated.

Meeting your nutritional needs from mostly whole, unprocessed foods will help meet your nutritional needs and reduce your intake of added sugars.

What about cancer prevention and recurrence?

The World Cancer Research Fund recommends limiting intake of sugar sweetened drinks, ideally avoiding them entirely. Sweetened drinks have been linked to weight gain. Excess body fat increases our risk of 13 different cancers.

Image source: Cancer Research UK

There is also increasing evidence that high glycaemic index (GI) carbohydrates can increase our risk of certain cancers. The good news is, by selecting lower GI and glycaemic load carbohydrates we can lower our risk. Check our our comprehensive Glycaemic Index Guide for more details, a savvy shopping guide and tips on how to tailor your plate.

Whilst it’s a good move to limit sugary foods and drinks as part of a healthy diet to avoid excess body fat, it’s less likely to have a meaningful impact on the growth or spread of cancer cells already present.

The bottom line

The statement that ‘sugar feeds cancer’ is an oversimplification of a highly complex process.

It suggests that cancer relies solely on sugar for growth. This is inaccurate.

It implies that by avoiding sugar, and therefore all carbohydrates sources, we can starve cancer cells. This may happen in a test tube when there’s no other fuel options, but in a complex human body with muscle and fat stores up for grabs, this simple statement can lead to dangerous food restrictions that can weaken our bodies physically, physiologically and mentally.

For specific advice for you, reach out to us today.

Tailor your plate with OnCore – your oncology nutrition experts.

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