Cancer is a leading cause of death worldwide, and the rate of obesity has doubled over the past 40 years.
Cancer experts say that keeping our weight down is one of the most valuable things we can do to reduce our risk of cancer.
Several studies have suggested a link between being overweight or obese and cancer, but the quality of some of the research has been questioned.
Reviewing the evidence
For the latest study, in The BMJ, a team led by Imperial College London reviewed 204 studies that had looked into an increase in body mass index (BMI), weight gain and waist circumference, and 36 cancers and their sub-types. Of these 95 studies were selected as being worth including.
They found that being 5 kg heavier than a healthy body weight increased the risk of rectal cancer in men by 9% and by 56% for cancers of the liver and gallbladder.
Obesity was also linked to oesophageal, womb and kidney cancers.
'Time for action'
In a linked editorial, Professors Graham Colditz and Yikyung Park from Washington School of medicine, St Louis, in the US, write: "Given the critical role of healthcare providers in obesity screening and prevention, clinicians, particularly those in primary care, can be a powerful force to lower the burden of obesity related cancers, as well as the many other chronic diseases linked to obesity such as diabetes, heart disease, and stroke.
"The data are clear. The time for action is now."
Dr Alison Tedstone, chief nutritionist at Public Health England, says in an emailed statement: "While this research provides yet more evidence of the link between obesity and some major types of cancer, more people need to be aware of the risk.
"Less than half the population realise that being obese increases the risk of cancer and, with almost two-thirds of adults carrying excess weight, this is worrying."
'Make small changes'
Dr Rachel Orritt, Cancer Research UK's health information officer, comments by email: "This research uses very strict criteria to evaluate the evidence and confirms that obesity increases the risk of cancer, linking many of the same cancer types that have been linked before.
"Being overweight is the second single biggest preventable cause of cancer after smoking. Whether it’s taking the stairs or switching to sugar-free versions of your favourite drinks, small changes can make a real difference, helping you keep a healthy weight and reducing your risk of cancer."
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