Together we will beat cancer


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This post has been updated on 11th July 2019 to add new study results on sugary drinks and cancer risk and on 9th November 2018 with the latest information on how Government is tackling sugar.

There’s a lot of confusing information and advice out there around sugar.

It’s been made the villain of our diet, but where does the consensus lie between how sugar and cancer are linked?

Does it cause cancer? Does sugar feed cancer cells, making them grow more aggressively? And how does the sugar we consume through food and drink affect our health, and what can be done about this?

In this post we’re taking a long hard look at sugar.

We’ll focus specifically on sugar and cancer, busting some myths and covering what researchers are studying in the hopes of finding new ways to treat people with cancer.

And we’ll cover why the amount of sugar in our diets is cause for concern. A high-sugar diet can be bad news when it comes to cancer risk, but not for the reasons that often appear in the headlines.

But first the basics, what our bodies need sugar for and where it comes from in our diet.

Glucose – the fuel of life

Search for sugar and cancer on the internet and it doesn’t take long to find alarming warnings that sugar is the “white death” and “cancer’s favourite food”.

But this idea that sugar is responsible for kick-starting or fuelling a cancer’s growth is an over-simplification of some complicated biology. Let’s start with what sugar actually is.

Sugar comes in many different forms. The simplest form is just as a single molecule, such as glucose and fructose. These molecules of simple sugars can also stick together, either in pairs or as longer chains of molecules. All of these combinations of molecules are carbohydrates, and are our body’s main source of energy.

The form of sugar most of us will be familiar with is table sugar, which is a simple sugar that dissolves in water and gives things a sweet taste. Its proper name is sucrose, and it’s made up of crystals of glucose and fructose. Table sugar is refined, meaning it’s been processed to extract it from a natural source (usually sugar beet). Unprocessed foods can be high in simple sugars too, for example honey (also made mostly of glucose and fructose) is nearly pure sugar.

As chains of sugar get longer, they lose their sweet taste and won’t dissolve in water anymore. These chains are called polysaccharides and form a large component of starchy foods. Starchy foods such as rice, bread, pasta and vegetables like potatoes might not taste sweet, but they are high in carbohydrate too.

Sugar, in some form, is in many things we eat. And this is good, because our bodies rely heavily on it to work.

Nearly every single part of our body is made of living cells. And it’s these cells that help us see, breathe, feel, think and much more.

While their jobs in the body may differ, one thing all these cells have in common is that they need energy to survive and perform their duties.

Cells somehow need to turn nutrients in our diet into a form of energy that they can use, called ATP. It would take a long time to explain this (if you’re interested you might want to read more), but simplistically the process starts with glucose.

Glucose is the basic fuel that powers every single one of our cells. If we eat or drink things that are high in glucose, such as fizzy drinks, the glucose gets absorbed straight into our blood ready for our cells to use. If a starchy food, such as pasta, is on the menu, the enzymes in our saliva and digestive juices break it down and convert it into glucose. And if for some reason there’s no carbohydrate in our diet, cells can turn fat and protein into glucose as a last resort, because they need glucose to survive.

It’s here that sugar and cancer start to collide, because cancer is a disease of cells.

Sugar and cancer

Cancer cells usually grow quickly, multiplying at a fast rate, which takes a lot of energy. This means they need lots of glucose. Cancer cells also need lots of other nutrients too, such as amino acids and fats; it’s not just sugar they crave.

Here’s where the myth that sugar fuels cancer was born: if cancer cells need lots of glucose, then cutting sugar out of our diet must help stop cancer growing, and could even stop it developing in the first place. Unfortunately, it’s not that simple. All our healthy cells need glucose too, and there’s no way of telling our bodies to let healthy cells have the glucose they need, but not give it to cancer cells.

There’s no evidence that following a “sugar-free” diet lowers the risk of getting cancer, or boosts the chances of surviving if you are diagnosed. 

And following severely restricted diets with very low amounts of carbohydrate could damage health in the long term by eliminating foods that are good sources of fibre and vitamins.

This is particularly important for cancer patients, because some treatments can result in weight loss and put the body under a lot of stress. So poor nutrition from restrictive diets could also hamper recovery, or even be life-threatening.

A sticky end for sugar research?

Although there’s no evidence that cutting carbohydrates from our diet will help treat cancer, important research has shown that understanding the abnormal ways that cancer cells make energy could lead to new treatments.

Back in the 50s, a scientist called Otto Warburg noticed that cancer cells use a different chemical process from normal cells to turn glucose into energy.

Healthy cells use a series of chemical reactions in small cellular ‘batteries’ called mitochondria. The Warburg Effect, as it was dubbed following Otto’s discovery, describes how cancer cells bypass their ‘batteries’ to generate energy more rapidly to meet demand.

This shortcut for making energy might be a weakness for some cancers that gives researchers an advantage for developing new treatments.

Firstly, it opens up the potential for developing drugs that shut down cancer cells’ energy-making processes but don’t stop healthy cells making energy. And researchers are testing drugs that work in this way.

Secondly, the abnormal processes in cancer cells can also leave them less able to adapt when faced with a lack of other nutrients, like amino acids. These potential vulnerabilities could lead to treatments too.

But these approaches are still experimental, and we don’t know yet if treatments that starve cancer cells are safe or if they work.

It’s certainly not grounds for cancer patients to try and do it themselves by restricting their diet during treatment – and going back to our earlier point, it could be dangerous to do so.

If sugar doesn’t cause cancer, why worry about it?

If cutting out sugar doesn’t help treat cancer, why then do we encourage people to cut down on sugary foods in our diet advice?

That’s because there is an indirect link between cancer risk and sugar. Eating lots of sugar over time can cause you to gain weight, and robust scientific evidence shows that being overweight or obese increases the risk of 13 different types of cancer. In fact, obesity is the single biggest preventable cause of cancer after smoking, which we’ve written about many times before.

And a study published in 2019 suggested there could be something else going on. Researchers found that people who drank more sugary drinks had a slightly increased risk of cancer, regardless of body weight. The study took weight in to account, but there are still lots of answered questions. More studies will be needed to investigate this. 

How can I cut down on added sugar?

It’s added sugar we’re mainly concerned with when it comes to weight gain, not sugar that is naturally found in foods like fruits and milk or healthy starchy foods like wholegrains and pulses (which people should be eating more of*).

One of the easiest ways to lower your added sugar is to cut down on sugary drinks, which are the largest source of sugar in the UK diet.

Some sugary drinks, such as fizzy drinks and energy drinks, can have more than the recommended daily maximum amount of added sugar in one serving alone. And while these extra calories promote weight gain, they offer no other nutritional benefits.

Multiple cues push us as customers to stack junk food into our shopping baskets, even if we weren’t planning to

– Professor Linda Bauld, Cancer Research UK

Other obviously sugary foods such as sweets, chocolate, cakes and biscuits are all best kept as treats too. But some foods that have hidden high amounts of added sugar may surprise you. Some breakfast cereals, ready meals (including ‘healthy’ ones), pasta sauces and yoghurts can have shocking amounts of sugar added to them. Reading nutrition information labels and checking the ingredients list can help you choose lower sugar options.

While there are steps you and your family can take to cut down on added sugar, making these changes can be easier said than done. And it’s here that governments need to lend a hand.

“Multiple cues push us as customers to stack junk food into our shopping baskets, even if we weren’t planning to,” says Professor Linda Bauld, our cancer prevention champion based at the University of Edinburgh. “That’s why we want the Government to help create a better food environment where the healthy choice is the easy choice for everyone.”

We’re delighted that the sugar tax, which came into effect in April 2018, has already had an impact, with some of the biggest drink companies changing their recipes to reduce sugar. The tax could prevent millions of cases of obesity, and obesity-linked cancers in the future, by reducing the amount of sugar the nation consumes in fizzy drinks.

But the Government hasn’t made much progress in its plan to reduce the amount of sugar in the types of foods that are very popular with children. One year into the programme, industry has failed to meet the voluntary targets set by Government, showing that a voluntary approach just isn’t as effective.

No sweet endings

The story about sugar and cancer is complicated.

On the one hand, sugar itself doesn’t cause cancer, and there’s no way (at the moment) of specifically starving cancer cells of glucose without harming healthy cells too.

There’s also no evidence that adopting a diet very low in carbohydrate will lower your cancer risk or help as a treatment. And for patients, getting adequate nutrition is important for helping their bodies cope with treatment.

But we’re concerned about the amount of added sugar people are consuming because it’s promoting weight gain. And being overweight or obese increases the risk of least 13 types of cancer.

So the take home message is that although banishing sugar won’t stop cancer in its tracks, we can all reduce our risk of getting cancer by making healthy choices, and lowering the amount of added sugar in our diets is a good way to help maintain a healthy body weight.


*While foods like fruit, milk and healthy starchy foods are high in carbohydrate, they have other important nutritional benefits. We should all be eating more whole fruits, vegetables, wholegrains and pulses as these nutritious foods are also high in fibre – this not only helps your body digest the natural sugar more slowly (which helps you keep a healthy weight), it also reduces the risk of bowel cancer.

Would you be interested in a podcast produced by Cancer Research UK?

We’re looking at new ways to tell stories about cancer and our work so we can improve the news and information we offer.

> Find out more about our future podcast


Gloria Hunter July 17, 2017

Really interesting and very informative for me and my husband who has had 3 types of cancer even though he has always been Heath conscious and not over weight. Myself however who has become overweight will definitely be more aware of added sugar in my diet.

David Barnes June 10, 2017

Absolutely appalling, dangerous article which could harm cancer patients health. Opinions is presented as “fact” and the detailed work of respected scientists is totally ignored and we are told it “does not exist”. Look at the work of Dr Valter Longo of University of Southern California, Professor Thomas Seyfried of Boston and Dr Dominic D´Agostino, Assistant Professor of Molecular Pharmacology, University of South Florida, and the Max-Plank Institute.

John Froster June 4, 2017

No scientific evidence? What about the review of 39 scientific papers – “The Efficacy of Ketogenic Diet…” (Varshneya et al. 2015) and Storer et al.’s 2916 paper “Ketolytic and Glycolytic Enzymatic Expression in Paediatric Ependymoma: Implication for Ketogenic Diet Therapy”?

wendi beal June 4, 2017

food for thought.

wendi beal June 4, 2017

very interesting report. food for thought.

wendi beal June 4, 2017

very interesting report.

Graham Cadd June 2, 2017

Great information, I will include this as part of my nutrition talks, you guys are Amazing.

Jan June 2, 2017

Informative and easy to understand.

Catherine Fuller June 2, 2017

This is an excellent article. I wish this would be given to the leaders in the ‘diet’ industry. Many people are misinformed in good health/exercise and nutrition. Many GP’s aren’t that knowledgeable about these things. So much conflicting advice from professionals.
This is my area of study and for the first time in a long time this article is one of the most accurate I’ve read. Thank you.

Angela Lander June 1, 2017

Very informative article, especially the molecular chain part. I gave my friend some bad advice I’m ashamed to say and will forward this to everyone I know. Keep up the fantastic work, we can stand up to cancer together with the info you are passing on.

Richard Bates June 1, 2017

Very very interesting and written in a way that doesn’t need a scientist’s brain to absorb.
Well done!

W. Clarke June 1, 2017

Sugar free has aspartame in and that causes cancer so what you’re saying is have diet foods which causes cancer which is a load of codswallop

Aliaksei Holik, PhD June 1, 2017

Being a researcher and a cancer researcher at that, I wonder what sort of evidence allows us to make that categorical statement that sugar doesn’t cause cancer directly, but obesity does. As far as I can see, these two factors are perfectly confounded. I.e. people who are obese are also, with some exceptions, people that consume large amounts of refined sugars. So unless we can run a study with a large cohort of obese people that have always been on sugar restricted diet, we have no way of separating these two risk factors.

Aine McCarthy May 23, 2017

Hi Stephen,

Thanks for your comment. The relationship between high insulin levels and cancer is complicated. Strong evidence shows that obesity causes 13 types of cancer and one of the leading explanations for how it causes cancer is due to growth hormones like insulin. Excess body fat can raise the level of insulin the body – this can tell cells to divide more often, which raises the chance that cells will change and lead to cancer. However there is no good evidence that people with normal insulin levels who eat sugar as part of a balanced diet are more likely to develop cancer.

The research into whether sugar in the diet makes cancer grow more aggressively is still at an early stage – it’s only been carried out in mice so we don’t know if the same is true in people. We would need more research to find out if reducing dietary sugar is safe, which patients might benefit, and whether it works as part of treatment.

Stephen M May 23, 2017

Sugar spikes insulin. Many cancers have elevated insulin receptors on the surface. Insulin is how sugar indirectly impacts cancer growth. Insulin also increases HGH and IGF – you can extrapolate what that would do to cancer. There is research from MD Anderson that shows fructose is the worst for someone with cancer and responsible for the cancer spreading. Interestingly fructose found in fruit. The health benefits of a diet that keeps blood sugar steady should be evident.

David Black May 19, 2017

This article was very informative and can hopefully give each reader reason to review certain types of food within their regular diet

TeeDee May 19, 2017

This article had the potential to be great, but fell short when it called Glucose, The Fuel of Life. There are many who consume zero carbs and are vibrantly healthy. Your statement that,”… following severely restricted diets with very low amounts of carbohydrate could damage health in the long term by eliminating foods that are good sources of fibre and vitamins.” is flat out false. There is no damage done to health when one eliminates or severely restricts carbohydrates. There is nothing in carbs that isn’t found in animal protein and the fibre myth has been debunked, though some like its filling effects (which healthy fats can also accomplish). Today’s dieticians, many doctors and health journalists are quickly becoming dinosaurs, but they don’t have to. Learn what is going on ‘now’, not what you learned in school or what is being told to you by those who want to stick with worn-out rules around food intake and health.

Yvie P May 19, 2017

This article asserts that “There’s no evidence that following a “sugar-free” diet lowers the risk of getting cancer, or boosts the chances of surviving if you are diagnosed.” I would be interested to read the reasearch illuminating this assertion. Please see research by Dr Valter Longo and Dr Thomas Sayfried for evidence based indications that sugars and cancer are linked.

Mary Edmans May 17, 2017

Interestingly the STAMPEDE series of clinical trials for advanced prostate cancer has been recruiting men to take part in a new arm which prescribes the diabetes drug metformin alongside chemo and hormone injections. We were told this is on the premise that inhibiting sugar might help slow cancer cell production. Not sure when the trial ends and the results will be published

Steven May 17, 2017

We must also remember that the liver converts food into glucose so the input of carbs do not have to be as much as the RDA.

Virginia May 17, 2017

Sucrose – table sugar- is NOT a simple sugar. It is a disaccharide, each molecule of which is two simple sugar molecules chemically bonded together. It is not a mixture of any sort. In the case of sucrose, it is made from glucose and fructose. To get the use of sucrose, the body breaks the bond between glucose and fructose, and changes glucose to fructose. Fructose enters mitochondria most easily and is broken down for energy use in that molecular form.

Fructose is found in fruits naturally. But manufacturers also use it as an added sugar ingredient at least in American foods as high fructose corn syrup. Since fructose is so easily absorbed by the body, it’s easy for large amounts of this sugar to sneak into our diets. This has caused many problems for Americans even eating the same foods as 40 years ago. They are not the same foods anymore, and much more sugar is found in canned and processed foods. I would not at all be surprised if produce is now sweeter than 40 years ago through variety development and plant cloning.

Check the first 3 or 4 ingredients on the packages of your food. If any one of them is sugar, high fructose corn syrup, corn syrup, or a worry ending in -ose, you have sugar as one of the main ingredients.

Even organic foods are not immune. A can of organic tomato paste I was going to buy had 2 ingredients: organic tomatos, and organic cane juice. Came juice is sugar cane, from which sucrose is refined. Both ingredients were organic, but it was high in sugar, so I couldn’t use it for my dish. I chose non – organic tomato paste instead, because it only had tomatoes in it.

Stay in the know. There are all kinds of tricky ways American food companies try to sell us junk. Reading about how things happen in America can possibly guard you from being taken in in the UK.

Best wishes from across the Pond!

Mark Z May 16, 2017

Good points. I’ve found though that the feelings of diabetes and the effects of cancer and radiation can feel very similar. If your blood sugar is high (ie jacked up due to steroids) you can do things to get the blood sugar in a normal range. The results can amaze because it not only can make you feel better but you get some control. Diet, exercise, and knowing your body and mindfulness can really help. Feelings of rage for example can come up when your sugar is outside normal,