Losing a significant amount of weight is often seen as a healthy change, but researchers have warned it could also be the opposite.
Those who lose more than a tenth of their body weight are 50 percent more likely than others to die from intestinal damage canceras shown by a German study.
Patients with the disease who to fall off also have a 33 percent greater chance of their cancer returning.
However, the scientists from the German Cancer Research Center emphasized that their findings do not mean that weight gain prevents colon cancer.
Rather, the significant weight loss in the months or years leading up to diagnosis is likely 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 an expected 3.2 million new diagnoses by 2040. The disease claims 17,700 lives every year in Britain alone.
For unclear reasons, colon cancer is increasing sharply among young people. It is believed that more than half of cases are preventable through diet and lifestyle changes.
Obesity is known to increase the risk of at least thirteen types of cancer, including colon cancer.
However, previous studies have identified the so-called ‘obesity paradox’, which describes the phenomenon of obese or overweight patients surviving longer with the disease than healthy weight patients.
Unexplained weight loss is a very real early warning sign of cancer that can affect survival outcomes
Experts think this is because people who carry 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 doctor for related health problems – such as diabetes, sleep apnea 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 diagnosis, which can transition someone from clinically overweight to a ‘healthy’ weight.
As a result, the healthy weight group ends up containing a disproportionate number of people who have already lost significant weight as a result of their cancer and therefore have a worse prognosis.
This can make overweight patients look healthier in comparison, the scientists claim.
In this study – published in the journal JAMA Network Open – researchers analyzed data from 5,521 people with colon cancer, who were followed for about five years.
Participants reported their height and weight at diagnosis, as well as their weight earlier in life, allowing researchers to estimate how much weight they had gained or lost in the five to 14 years before diagnosis.
The results showed that patients who had lost more than 10 percent of their body weight before diagnosis had a 55 percent higher risk of dying from any cause than those whose weight had remained stable.
They were also 51 percent more likely to die from their disease and 33 percent more likely to have their cancer return.
However, when the researchers took into account the weight loss that occurred before diagnosis, the apparent survival benefit of being overweight disappeared.
They concluded that the so-called obesity paradox is more likely due to weight loss caused by hidden cancer, rather than obesity conferring any survival benefit.
They added: ‘Apparent survival benefit associated with a higher BMI at diagnosis should not be used as evidence to suggest that weight gain would be beneficial.’
More than 44,000 people in Britain are diagnosed with bowel cancer every year.
Obesity, lack of exercise and excessive alcohol consumption have been shown over time to increase the risk of the disease.
And until recently, all research suggested that the risk of developing colon cancer increases with age.
But now people under 49 in Britain are around 50 percent more likely to get bowel cancer than people of the same age in the early 1990s.
Obesity is the only known behavioral risk factor to have increased 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 declining.
Maintaining a healthy weight has been shown to prevent about 20 percent of colon cancer cases, but experts say obesity alone is not enough to explain the overall increase, indicating there may also be unknown causes, including early life exposure.
