Being overweight could actually help people battle cancer, according to a new study.

Although a high body mass index (BMI) is linked to cancers, diabetes, cardiovascular and other diseases, it seems it is not always bad to be fat.

Surprised researchers at the Flinders Centre for Innovation in Cancer in Australia found that more obese cancer patients responded better with the drug atezolizumab than thinner sufferers.

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Atezolizumab - also known by the brand name Tecentriq - is a common immunotherapy treatment for non-small-cell lung cancer (NSCLC).

The surprising result, published in the journal JAMA Oncology, is in stark contrast with widespread cancer health warnings for those who are overweight or obese.

Earlier this year, Cancer Research UK faced an online backlash over "fat-shaming" when it launched a new campaign warning that 'obesity is cause of cancer too', with the slogan emblazoned across a mocked-up cigarette packet.

Lead investigator Dr Ganessan Kichenadasse, a medical oncology researcher at the Flinders Centre, said: "This is an interesting outcome and it raises the potential to investigate further with other cancers and other anti-cancer drugs.

"We need to do further studies into the possible link between body mass index (BMI) and related inflammation, which might help to understand the mechanisms behind paradoxical response to this form of cancer treatment."

Of the 1,434 participants studied, 49 per cent were normal weight, 34% were overweight and 7% were obese.

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Dr Kichenadasse said that it adds to the theory of the "obesity paradox", whereby cancer can be both worsened and helped by being fat.

He said: "Previous studies have explored a concept called the 'obesity paradox' where obesity is associated with increased risks for developing certain cancers and, counter-intuitively, may protect and give greater survival benefits in certain individuals.

"Our study provides new evidence to support the hypothesis that high BMI and obesity may be associated with response to immunotherapy."

The team found NSCLC patients with high BMI in four clinical trials had a significant reduction in mortality with atezolizumab.

The obesity paradox was first described in 1999 in overweight and obese people undergoing kidney dialysis, and has subsequently been found in those suffering from heart failure, heart attacks, acute coronary syndrome, chronic obstructive pulmonary disease (COPD) and in older nursing home residents.

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In people with heart failure, those with a BMI between 30-35 - categorised as obese - actually had lower mortality than those with what would normally be considered an ideal weight.

However, the theory is controversial. In particular, studies where it has been observed have sometimes been criticised for failing to take into account the tendency of smokers - who have higher average mortality rates - to also be leaner.

As a result, studies which have made inadequate adjustments to account for smoking rates among participants would tend to lead to an underestimate of the risk associated with being overweight and obese.

Notably, an analysis of 1.46 million individuals who had never smoked greatly reduced the mortality estimates in the underweight group, as well as strengthening the estimates in the overweight and obese groups.

Dr Kichenadasse said their finding "warrants more studies into the potentially protective role of high BMI in other cancer treatments".

The latest statistics indicate that 29% of Scottish adults are obese. While an increase in cancer incidence is mainly blamed on the ageing population, there has also been an 11% increase in cancer rates over the past 20 years among young adults aged 30 to 45 who are heavier than previous generations but smoke less.