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Sugar and cancer. What’s the real story?

sugar and cancer

Could your favourite sugary snack directly lead to cancer? Here we bust the myths and explore the science underpinning the not-so-sweet story.

What is sugar?

There is a lot of confusing and conflicting advice about sugar and whether it is a cancer-causing villain in our diet that should be removed entirely. Sugar, in some form or another, is in a lot of things we eat, and this is positive as our living cells rely heavily on it for energy to function properly. Glucose (often deemed ‘the fuel of life’) [1] is a form of sugar and it is this that powers every single one of our cells. 

Is there a direct link between sugar and cancer?

Cancer cells usually grow at a fast rate and therefore require a lot of glucose for energy. This is where the hypothesis was posed that sugar fuels cancer- if cancer cells need lots of glucose, would removing sugar from our diets stop cancer cells from being able to grow? [2] The biology is NOT as simple as this. All of our healthy cells need glucose too. We cannot tell our healthy cells to have the glucose they need but not allow cancer cells to have it and there is no evidence that following a ‘sugar-free’ diet will prevent you from getting cancer [3]. In fact, extreme restriction in your intake of carbohydrates could potentially be more harmful to you, particularly if you are a cancer patient as some treatments put the body under stress and you need good sources of fibre and vitamins. 

A study published in recent years in the journal Nature Communications brought the ‘direct link between sugar and cancer’ debate back to attention [4]. The nine-year research project suggested that a biological mechanism in yeast cells may explain a relationship between sugar and tumours [5]. The study looked at the ‘Warburg effect’, a discovery that cancer cells can use a different chemical process from normal cells to turn glucose into energy [6]. Rather than respiring, they can switch to fermentation- a process that yeast grow fastest at. The data from this study is exciting as it opens the doors for potentially developing drugs that can shut down cancer cell’s energy-making processes without affecting healthy cells. This study still does not conclude though that sugar fuels cancer. When the senior author of the study- Johan M. Thevelein- was asked if he believes that eating more sugar leads to more cancer, he said this was definitely not stated in the paper [7]. The paper instead explains how normal, healthy cells can handle sugar in a controlled way.

The approaches to creating cancer drugs based on the research conducted in this study are still experimental and it is not yet known if starving cancer cells in this way will work. The paper should not be interpreted as advice to cut out all sugar from your diet, as stated this could be dangerous, particularly for cancer patients.

Is there an indirect link between sugar and cancer?

So, we have established that no evidence yet proves a direct link between sugar and cancer, but could there be an indirect link? If cutting out sugar doesn’t help to prevent or treat cancer, why are we often encouraged not to consume too much of it?

The answer is that eating lots of sugar over time can cause you to gain weight and strong scientific evidence shows that being overweight and obese increases the risk of 13 types of cancer, including breast, liver and colon cancer [8]. This is because fat cells release inflammatory proteins that can damage DNA and eventually cause tumours. The more fat cells you have, the more of these proteins you are likely to have. So, any potential link between sugar consumption and prevalence of cancer is indirect through the process of weight gain. 

Should we worry about sugar?

Thevelein, the senior author of the aforementioned paper on cancer cells suggests that it is better to not eat too much sugar so that you are at less risk of becoming obese. However, he also suggests that cancer patients eat fewer simple sugars and more complex sugars like those found in starch and whole grains [7]. These complex sugars are released and taken up by the body more slowly, which might be helpful to cancer patients. The message of his team that conducted the nine-year research project is therefore that we should try to look for alternative ways of providing sugar and energy to cancer patients rather than rapidly metabolized simple sugars BUT also that cutting out all sugar from your diet is not the way forwards.

What is the right amount of sugar to consume?

According to NHS England, adults should have no more than 30g of free sugars (those added to food or drinks) a day [9]. This is roughly equivalent to 7 sugar cubes. Free sugars are found in foods such as sweets, biscuits, chocolate, cakes and sugary drinks and it is these that we should cut down on rather than natural sugar found in foods like fruits, milk or healthy starchy foods like wholegrains.

How can we cut down on added sugar?

One of the best ways to lower your added sugar is to cut down on sugary drinks, which have been found to be the largest source of sugar in the UK diet [10]! Some fizzy drinks have more than the recommended daily maximum amount of added sugar in just one serving and these extra calories not only promote weight gain but also rarely offer other nutritional benefits. 

Some foods also have hidden high amounts of added sugar that may surprise you, which is why it is important to read food labels and look for hidden sugars, such as those in some breakfast cereals, pasta sauces and ready meals. Reading nutrition information labels can help you to choose lower sugar options [11].

Is there a sweet ending to this research?

The story about sugar and cancer is complicated- sugar itself doesn’t cause cancer directly and there is no evidence that adopting a diet with no sugar/ very low in carbohydrates will lower your cancer risk but there does seem to be an indirect link in terms of being overweight. The RYH programme therefore includes sugar in recipes as when eaten in small amounts it can fit into a balanced diet, but the recipes promote the options of more natural sugars rather than processed foods. This way, you will get more of the nutrients your body needs to reduce your cancer risk in addition to satisfying any cravings. 


[1] Goncalves M, Hopkins B, Cantley L. Dietary Fat and Sugar in Promoting Cancer Development and Progression. Annual Review of Cancer Biology. 2019;3(1):255-273.Available:
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[2] Makarem N, Bandera E, Nicholson J, Parekh N. Consumption of Sugars, Sugary Foods, and Sugary Beverages in Relation to Cancer Risk: A Systematic Review of Longitudinal Studies. Annual Review of Nutrition. 2018;38(1):17-39.
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[3] Theodoratou E, Timofeeva M, Li X, Meng X, Ioannidis J. Nature, Nurture, and Cancer Risks: Genetic and Nutritional Contributions to Cancer. Annual Review of Nutrition. 2017;37(1):293-320.
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[4] Peeters K, Van Leemputte F, Fischer B, Bonini B, Quezada H, Tsytlonok M et al. Fructose-1,6-bisphosphate couples glycolytic flux to activation of Ras. Nature Communications. 2017;8(1).
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[5] Mboge M, Bissell M. The not-so-sweet side of sugar: Influence of the microenvironment on the processes that unleash cancer. Biochimica et Biophysica Acta (BBA) – Molecular Basis of Disease. 2020;:165960.
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[6] Koppenol W, Bounds P, Dang C. Otto Warburg’s contributions to current concepts of cancer metabolism. Nature Reviews Cancer. 2011;11(5):325-337.
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[7] Susan Scutti C. Is there a link between sugar and cancer? [Internet]. CNN. 2020 [cited 10 September 2020]. Available from:

[8] Parekh N, Chandran U, Bandera E. Obesity in Cancer Survival. Annual Review of Nutrition. 2012;32(1):311-342.
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[9] Sugar: the facts [Internet]. 2020 [cited 10 September 2020].
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[10] Chazelas E, Srour B, Kesse-Guyot E, Julia C, Deschamps V, Galan P et al. Sugary drink consumption and cancer risk: results from NutriNet-Santé prospective cohort. European Journal of Public Health. 2019;29(Supplement_4).

[11] Buyken A, Mela D, Dussort P, Johnson I, Macdonald I, Stowell J et al. Dietary carbohydrates: a review of international recommendations and the methods used to derive them. European Journal of Clinical Nutrition. 2018;72(12):1625-1643.