Does sugar feed cancer?


Does sugar feed cancer?

By Jane Clarke

June 26, 2017


I’m thrilled to have been asked by Macmillan Cancer Support to join their Ask an Expert panel, offering insight on nourishing solutions to help when you are living with cancer. As well as answering questions for members of the Macmillan community, I will be filming a series of videos on common issues around eating when you are being treated for cancer or you’re in recovery. This is an unpaid, voluntary role but one I’m honoured to accept because of the immensely valuable support that Macmillan gives to those affected by cancer.


Do take a look at the first episode, which tackles the vexed issue of sugar and cancer, and the idea that sugar ‘feeds’ cancer cells. The relationship between sugar and cancer is a subject of ongoing scientific research and the need for many of us to cut down on high-sugar foods such as cakes, biscuits and chocolate, as well as sugary drinks, is well recognised. But currently there is no strong, definitive evidence to show that cutting sugar from the diet can ‘starve’ tumours. This is why well-respected cancer charities such as Macmillan Cancer Support and Cancer Research UK, the majority of oncologists in hospitals in the UK and worldwide, and dieticians like myself who work with cancer patients, do not advocate a complete ban on sugar for people living with cancer, although I recognise some professionals think differently.

My approach is to support patients with evidence-based nutritional strategies to help them cope with treatments and live with cancer. It’s based on the following scientific views from the cancer community:

Consuming too much sugar is linked with weight gain and being overweight puts us at greater risk of developing certain forms of cancer. There is also some evidence that consuming large amounts of sugar is linked to increased risk of certain cancers, including oesophageal cancer. However, that doesn’t mean that consuming sugar ‘feeds’.

Associations have been shown between high blood sugar (glucose) levels and an increased risk of some types of cancer. However, these studies have not demonstrated a causal effect of blood glucose or any direct link with the amount of sugar in the diet.

The body has evolved fantastically to maintain a certain level of glucose in the blood. The process begins when carbohydrate is absorbed into the body in the form of sugar. As blood sugar levels rise, the pancreas produces insulin, a hormone that prompts cells to absorb blood sugar for energy or storage. As cells absorb blood sugar, levels in the bloodstream begin to fall and the pancreas starts making glucagon, another hormone that signals the liver to start releasing stored sugar. This process ensures that cells throughout the body have a steady supply of energy to function.

If the body doesn’t have enough carbohydrate, it will use its existing resources to produce glucose – it’s a natural back-up plan to prevent your blood sugar dropping below a certain level. The result is that, unless you are living with diabetes, where control of blood glucose is impaired, it’s actually very difficult to alter your blood glucose levels significantly by changing your diet.

What you eat and drink can influence short-term rises in blood glucose. Generally, foods with a high glycaemic index (like bananas, popcorn and dried fruit) can cause spikes in blood glucose, while foods with a low glycaemic index (such as apples, beans and lentils, and green leafy vegetables) are digested more slowly, prompting a more gradual rise in blood sugar. This is why the latter are advised for people with diabetes, to help control their blood sugar levels. In practice, many factors can influence a food’s GI and, of course, we mostly eat foods in combination, rather than on their own.

Cancer cells do take up more glucose than other cells because they grow and divide at a faster rate. However, they are able to obtain glucose from other sources in the body apart from sugar, for the reason outlined above. And while carbohydrates (sugar and starches) are the body’s primary source of energy, fats and protein can also be broken down by the body to provide energy stores. Even without any carbohydrate in the diet, your body will make sugar from other sources, including protein and fat.

Cancer cells use glucose differently than other body cells and this cancer metabolism is being researched to see if it can help develop new treatments for the disease. But there is no convincing evidence to date that depriving our body of sugar will slow tumour growth.

Before a PET scan, which is used to look at cancer in the body, you will be injected with a small amount of radioactive trace, typically a form of glucose. All tissues in your body absorb some of this tracer, but tissues that are using more energy — including cancer cells — absorb greater amounts, which allows them to be identified by the scan. For this reason, some people have concluded that cancer cells grow faster when we eat more sugar. But studies have shown this isn’t true.

Some people living with cancer may be prescribed Metformin, a drug which changes the way in which the body deals with sugar from our diet. But current medical advice about moderate sugar intake does not change when this drug is prescribed.

None of us should eat too much sugar because of its link to insulin resistance and Type 2 diabetes, increased risk of certain cancers, weight gain and tooth decay (with may be a factor in developing heart disease). It can also cause our blood sugar to fluctuate (within the parameters explained above), leading to energy highs and lows. However, sugar can be enjoyed as part of a balanced diet that contains plenty of fresh vegetables and fruit, protein and wholegrains. We need to be careful about suggesting the avoidance of certain foods, particularly when people are struggling to maintain weight due to the side effects of dealing with cancer and its treatment.

I recommend enjoying a sweet treat that has additional nutritional benefits, like a wonderful frozen yoghurt made with antioxidant-packed berries. Avoiding too many high-GI foods that release their sugar quickly into the bloodstream, or eating them with fibre and protein to slow absorption of sugar, is also a good idea – a sticky Medjool date stuffed with a walnut or mascarpone is a classic carb-protein combination and just the thing when you need an energy boost. You could also use different ingredients to add sweetness to your foods – coconut, cinnamon and almond milk, to name a few. I’ve written more about sugar here.

For more insight into the science of sugar and sugar, it might also be worth looking at these articles:

No Sugar, No Cancer? A look at the evidence an interview with Memorial Sloan Kettering President Craig Thompson, an expert in cancer metabolism

10 Persistent Cancer Myths Debunked: Cancer has a sweet tooth by Cancer Research UK

sugar and strawberries


Here is a transcript of the video

Hello. I’m Jane Clarke, a nutritionist and dietician and a food writer, and I have looked after patients living with cancer for over 25 years.

When you are going through cancer treatment, food can become a real battleground, so I’d like to talk to you about the types of foods that could help soothe, and also just make help coping with cancer and the treatments you have to go undergo that bit easier.


Episode 1: Sugar

I see patients who are so are so afraid of having something that is sweet, there is so much information on the web that tells you when you have cancer you must not have sugar and that just not the case, sugar doesn’t feed cancer cells, it doesn't cause tumors to grow any quicker.

When we are looking at the diet we want to try and be wise about sugar, so if you've got a real craving for sugar, don’t have too much of it. Sometimes we can fall into the trap of the day being loaded with very sweet foods, and that just means that you’re not having enough of the other stuff, the nourishing proteins, the other vegetables and fruits. The things that your body whilst you're living with cancer desperately needs you to have a balance of.

One trick that I use with my patients is to keep a little note of what they’re eating and drinking, and also ask the question “why are you eating or drinking it” just by asking yourself that question you can find that it just reduces the volume.


Natural sugars

When you search the term natural sugars on the internet, you come across all different types of sugar from honey, agave, coconut sugar, different fruit concentrates. Some of the articles on the internet imply that these are much better for you. The body actually metabolizes them pretty similarly to refined sugar. Sugar isn't bad for you when you have cancer, and it can be a useful source of energy.


Lack of appetite & weight loss

When you have undergone cancer treatment, so this could be chemotherapy, radiotherapy, immunotherapy, if you've had surgery, it can be the case that youve lost a lot weight. When you've lost a lot of weight your body can get into this little vicious cycle so that you don't eat much, you feel very weak, you don't feel like eating much. You keep on going round and round and keep on losing weight, so we need to find a way to break this vicious cycle because the food that you put inside your body has a big impact on how strong you feel. A little sweet some something can be a way of convincing the body that it’s going to want to eat.


Steroids and Sugar

Sometimes when you are undergoing cancer treatments, you might need to have some steroids. Steroids can have an affect on the body that can sometimes causes your body to show raised sugar levels. So your care team, your nurse, your oncologist might say that you need to watch the sweet stuff. SO choose something that you really fancy, a favourite sweet thing and have a little bit of it, and having a sweet food like a pudding or a piece of cake after a meal that’s got some protein in it. These protein rich foods can slow down the absorption of the sugar, so that can make it easier for your body to cope with the challenge of having something sweet inside it.


Sweet treats with nutritional benefits

One of the best ideas is to look for a sweet food that has some additional benefit to it, it could be a sorbet that you have made using some amazing berries that youve got out of the freezer, or if you're making a meringue put lots if fresh fruit and some cream on top and the cream will slow down the absorption of the sugar. All these tricks of the trade can really help you have something that you quite fancy and gives you some beneficial calories.


Ask the expert

So if you've got any questions about sugar, ask the question in the comments box below, I’m one of the experts in the online community, so ask me a question, I’m here.

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