Patient FAQs about obesity and cancer

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Patients may come to you with questions about the link between obesity and cancer and might have questions about what it means for them. Here are some questions that could be asked.

Overweight and obesity is the UK’s biggest preventable cause of cancer after smoking - it causes 6% of cancer cases in the UK each year.[1]

References

[1] Brown, K. et al. The fraction of cancer attributable to modifiable risk factors in England, Wales, Scotland, Northern Ireland, and the United Kingdom in 2015. Br. J. Cancer 118, 1130–1141 (2018).

No. Smoking carries a much higher risk of cancer than obesity and is still by far the biggest preventable cause of cancer in the UK. However, after smoking, obesity is the next biggest preventable cause. And for some types of cancer, breast and womb, it is the biggest preventable risk factor.[1]

References

[1] Brown, K. et al. The fraction of cancer attributable to modifiable risk factors in England, Wales, Scotland, Northern Ireland, and the United Kingdom in 2015. Br. J. Cancer 118, 1130–1141 (2018).

Overweight and obesity is linked to 13 types of cancer.[1] The full list of cancers caused by obesity is: breast (in women after the menopause), bowel, pancreatic, oesophageal (food pipe), liver, kidney, upper stomach, gallbladder, womb, ovarian, thyroid, multiple myeloma (a type of blood cancer) and meningioma (a type of brain tumour).

References

[1] Secretan, B. L. et al. Special Report Body Fatness and Cancer - Viewpoint of the IARC Working Group. (2016).

There is consistent data from decades of prospective research[1] involving millions of people which means other things that could explain the association, such as a chance finding or things like diet or physical activity, can be confidently ruled out as explanations. In addition, a dose-response relationship has been found, meaning the more weight gained the higher the risk, and there are good explanations for how obesity could cause cancer. Using this type of causal criteria, other world leading authorities on cancer research like the International Agency for Research on Cancer[2] and the World Cancer Research Fund[3], have come to similar conclusions about the evidence linking cancer and obesity.

Factors that cause cancer- whether that’s tobacco, obesity, alcohol or the sun - increase an individual person’s risk of cancer, but do not mean that person will definitely develop cancer. Lots of things make an individual’s personal risk of cancer and in most cases we can’t know what has caused an individual person’s cancer. But at a population level, being exposed to a risk factor causes more people to develop cancer.[4]

See more about the does-response relationship findings

See more on how obesity could cause cancer

References

[1] Renehan, G. et al. Body-mass index and incidence of cancer: a systematic review and meta-analysis of prospective observational studies. Lancet 371, 569-578 (2008).

Bhaskaran, K. et al. Body-mass index and risk of 22 specific cancers: A population-based cohort study of 5·24 million UK adults. Lancet 384, 755–765 (2014).

 [2] Secretan, BL. et al. Special Report Body Fatness and Cancer - Viewpoint of the IARC Working Group. (2016).

[3] World Cancer Research Fund. Body fatness and weight gain and the risk of cancer. (2018).

[4] Brown, K. et al. The fraction of cancer attributable to modifiable risk factors in England, Wales, Scotland, Northern Ireland, and the United Kingdom in 2015. Br. J. Cancer 118, 1130–1141 (2018).

Overweight and obesity is measured by body mass index (BMI). BMI is calculated by a person’s weight in kilograms divided by height in metres squared. Overweight is classified as having a BMI between 25.0 and 29.9. Obesity is classified as having a BMI of 30 and over.

BMI = weight (in Kg) / height (in M2)

For children, it’s a bit more complicated as things like whether or not they have started puberty are also important. So, their age and gender is also taken into account, with their BMI converted into a ‘centile’, such as those used on a child’s growth chart.

In the UK today more than 6 in 10 adults are overweight or obese and around 3 in 10 children. An obese child is around 5 times more likely to be obese as an adult.

Whilst BMI is not a perfect measure of body fat, it is a useful guide for most adults. However, it isn’t appropriate for certain groups, such as professional athletes.

BMI is used in most scientific studies linking body fat with health outcomes. Studies using other measures of body fat, such as waist measurements, have found similar links with cancer to studies using BMI.

The risk is greater the more overweight you are, and the longer you are overweight for. But that doesn’t mean the damage is done. You can help stack the odds against cancer by avoiding gaining more weight, and it is also a good thing to do for your health generally. The evidence for how weight loss could impact the risk of cancer is growing and so far suggests weight loss can help reduce cancer risk. Also the things you can do to lose weight, such as eating and drinking healthily can reduce the risk of cancer on their own. So weight loss is worth it if you’re overweight or obese. But more research is needed to know exactly how weight loss impacts cancer risk.

There are lots of other steps you can take to reduce the risk of cancer- things like not smoking, cutting down on alcohol and staying safe in the sun can all make a big difference.

No one is ever to blame for their cancer. For most people, we can’t know what has caused their cancer. There are lots of factors that make up your personal risk of cancer. Everyone’s personal risk depends on a combination of our genes, our environment, our age and factors like whether we smoke or what our weight is.

Being overweight or obese doesn’t mean that you will definitely develop cancer. There are lots of factors that make up your personal risk of cancer. Some things you can’t change, like your family history and your age. But while there are no guarantees against cancer, there are steps you can take to reduce the risk of cancer and stack the odds in your favour- things like not smoking, eating healthily and cutting down on alcohol. Evidence so far shows losing weight can also help reduce the risk, and the steps most people take to lose weight like eating and drinking healthily also reduce cancer risk on their own. It’s never too late to make changes, and even small things can add up to a big difference if you do them most days.

See more information for patients about risk and lifestyle changes

Being overweight or obese causes around 22,800 cases of cancer every year in the UK [1]. Being overweight or obese can increase the risk of cancer, independent of other things, like diet. There are a number of ways it is thought to do so – for example, extra fat in the body can cause greater levels of hormones and inflammation, which can increase the risk of cancer cells developing. But a healthy diet, including one with more fruit and vegetables, can help us to keep a healthy weight and affect our risk of cancer directly, although to a lesser extent that obesity- around 11,700 cases of bowel cancer are caused by diets low in fibre and around 5,400 cases of bowel cancer are caused by eating too much processed meat every year in the UK [2].

References

[1] Brown, K. et al. The fraction of cancer attributable to modifiable risk factors in England, Wales, Scotland, Northern Ireland, and the United Kingdom in 2015. Br. J. Cancer 118, 1130–1141 (2018).

[2] Cancer Research UK. Bowel cancer risk (2018)

Many people believe that getting cancer is purely down to genes, fate or bad luck. But through scientific research, we know that our risk actually depends on a combination of our genes, our environment and things such as smoking or weight, which we’re more able to control.

Cancer is caused by damage to our DNA, the chemical instructions that tell our cells what to do. Things we come into contact with such as UV rays, or the cancer-causing chemicals in tobacco, can damage our DNA. This damage can build up over time. If a cell develops too much damage to its DNA it can start to grow and multiply out of control – this is how cancer starts.

In the UK, more than 1 in 2 people born after 1960 will develop cancer at some point in their lives. Every year, around more than 360,000 people are diagnosed with the disease. But experts estimate that around 4 in 10 cancer cases could be prevented, largely through changes like not smoking, keeping a healthy weight, staying safe in the sun and cutting down on alcohol [1].

 References

 [1] Cancer Research UK. Cancer risk (2018)

The link between obesity and cancer comes from very large studies involving millions of people. When we look at a population level, we can see that cancer is more common in people who are overweight or obese. But this doesn’t mean that everyone who is overweight will definitely develop cancer, or that you can only have cancer if you are overweight.

It’s also important to understand that unintentional weight loss can be a common symptom of cancer, so just before a diagnosis of cancer or while undergoing treatment, many people may lose a lot of weight.

See more on how being overweight caused cancer

No. The link between obesity and cancer is only in adulthood. But a healthy weight is important for children too. One in five children are overweight or obese before they begin primary school, and one in three children are overweight or obese by the time they leave [1]. An obese child is 5 times more likely to become obese as an adult [2].

 References

 [1] NHS Digital. National Child Measurement Programme - England, 2015-16.

[2] Simmonds M et al. Predicting adult obesity from childhood obesity: a systematic review and metaanalysis. Obesity Reviews (2016)

don’t know what causes, or how to prevent most childhood cancers and no one should feel blamed for their child’s cancer. While sadly all ages can develop cancer, it is much more common in older people- half of cancer cases in the UK are diagnosed in people over 70.

Being overweight or obese increases the risk of 13 different types of cancer in adulthood, including common types like breast and bowel [1]. But a healthy weight is important for children too. One in five children are overweight or obese before they begin primary school, and one in three children are overweight or obese by the time they leave [2]. Children who are obese are around 5 times more likely to grow into adults who are obese [3].

References

[1] Secretan, B. L. et al. Special Report Body Fatness and Cancer - Viewpoint of the IARC Working Group. (2016).

[2] NHS Digital. National Child Measurement Programme - England, 2015-16.

[3] Simmonds M et al. Predicting adult obesity from childhood obesity: a systematic review and metaanalysis. Obesity Reviews (2016)

Making individual healthy choices is important. And there are steps you and your family can take right now to keep healthy. Even small changes you can stick with can make a big difference.

But it’s not just up to us individuals and reducing levels of obesity will take collective action, starting with strong political willpower. This is because the world we live in doesn’t make it easy to be healthy, and the odds are stacked against us all when it comes to making healthy choices. In fact, most people struggle to keep a healthy weight in the UK. There are plenty of things beyond our personal control that influence what we eat and how much we move- things like food advertising, price promotion, how accessible food is to you and levels of sugar, fat and salt added to food and drinks. All these things can influence what you put in your shopping trolley, and for the most part nudge you to choose unhealthy choices. That’s why we need the government to act to better regulate the food, drink and advertising industries, so that the healthy choice is the easy choice for everyone.

See our top tips for changes you can make

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