Experts reveal how to tell if your weight loss is actually a sign of deadly bowel cancer that's on the rise

Losing a significant amount of weight is often seen as a healthful change - but researchers have warned it could be the opposite. Those who lose more than a tenth of their body weight are 50 per cent more likely than others to die from bowel cancer, a German study has found. Patients with the disease who lose weight also have a 33 per cent greater chance of their cancer returning. However, the scientists, from The German Cancer Research Centre, stressed that their findings don't mean gaining weight prevents bowel cancer.Rather, that significant weight loss in the months or years prior to diagnosis is likely to be a little-known sign that the disease is attacking the body - and should not be ignored.Bowel cancer is the third most common cancer in the world, with new diagnoses expected to reach 3.2 million by 2040. The disease claims 17,700 lives in the UK alone every year. For reasons that remain unclear, bowel cancer is rising sharply in young people. More than half of cases are thought to be preventable through changes to diet and lifestyle. It is well-known that obesity increases the risk of at least 13 cancers, including bowel cancer. However, previous studies have identified what's been dubbed the 'obesity paradox', which describes the phenomenon of obese or overweight patients surviving longer with the disease than those of a healthy weight. Unexplained weight loss is a very real early warning sign of cancer that can impact survival outcomes Experts believe this could be because people carrying extra weight are better able to withstand the physical toll of cancer and its aggressive treatments. People with obesity also tend to have more contact with their GP because of related health conditions - such as diabetes, sleep apnoea and high blood pressure - potentially leading to an earlier diagnosis. However, experts have long argued that the so-called 'obesity paradox' may be an illusion. Many patients will unintentionally lose weight in the years before they are diagnosed, which can shift someone from being clinically overweight to 'healthy' weight.As a result, the healthy-weight group ends up containing a disproportionate number of people who have already lost a significant amount of weight as a result of their cancer and therefore have a poorer prognosis. This can make overweight patients look healthier by comparison, the scientists argue.In this study - published in the journal JAMA Network Open - researchers analysed data from 5,521 people with bowel cancer, who were followed for around five years. Participants reported their height and weight at diagnosis, as well as weight earlier in life, allowing researchers to estimate how much they had gained or lost in the five to 14 years before diagnosis. Results showed patients who had lost more than 10 per cent of their body weight in the before diagnosis had a 55 per cent higher risk of death from any cause, than those whose weight had remained stable. They were also 51 per cent more likely to die from their disease and had a 33 per cent greater chance of their cancer returning. However, when the researchers accounted for weight loss that occurred prior to diagnosis, the apparent survival benefit of being overweight disappeared. They concluded that the so-called obesity paradox is more likely to be due to weight loss caused by hidden cancer, rather than obesity conferring any survival advantage. They added: 'Apparent survival advantage associated with higher BMI at diagnosis should not be used as evidence to suggest that weight gain would be beneficial.' More than 44,000 people are diagnosed with bowel cancer in the UK every year. Obesity, lack of exercise and excessive alcohol consumption have all been shown, over time, to raise the risk of the disease. And, until recently, all research suggested the chances of developing bowel cancer rises with age. However, now, in Britain, those under 49 today are around 50 per cent more likely to develop bowel cancer than people of the same age in the early 1990s. Obesity is the only known behavioural risk factor that has been increasing in younger adults over the past two decades - while more established risks such as smoking, alcohol consumption, and physical inactivity have all remained stable or in decline. Maintaining a healthy weight has been shown to prevent around 20 per cent of bowel cancers, but experts say obesity alone is not sufficient to explain the overall rise, indicating that there may also be unknown causes including early life exposures.