While it might sound counterintuitive, losing weight may raise the risk of cancer, a study has suggested.
Researchers from Harvard found that health professionals in their 40s and beyond who lost more than percent of their body weight had a 57 percent higher rate of cancer a year later compared to those who stayed the same weight.
The risk of cancer of the esophagus, stomach, liver, biliary tract, or pancreas specifically was also higher.
While the study needs to be explored further, the academics said people should not be put off dieting in their 60s.
It may have been the cancer itself causing the weight loss. When tumors begin to grow, particularly in the digestive system, it can lead to a loss of appetite.
Researchers from Harvard in Boston found that health professionals who lost weight had a significantly higher risk of cancer in the year after, compared with those without recent weight loss
The above graph shows the cancer diagnosis rates (top lines) and fatality rates (bottom lines) for males (red) and females (blue) since the start of this century. It reveals that fatality rates are trending downwards overall, while case rates are steady
And being obese has been linked to several common cancers including breast, colorectal, esophageal, kidney, gallbladder, uterine, pancreatic, and liver cancer.
Multiple previous studies have shown that losing weight actually reduces the risk of cancer.
In the most recent study, a group of female nurses aged 40 and above were followed from 1978 to 2016, and a group of male healthcare professionals were followed from 1988 to 2016, making a total participant pool of more than 157,000 participants.
Healthcare professionals were followed because the researchers said that ‘weight loss is common in primary care.’
The participants reported their weight every two years and were followed for an average of 28 years.
During the year after the weight loss, there were 1,362 cancer cases per 100,000 person-years among all participants who had recently lost more than 10 percent of their body weight.
This was compared to 869 cancer cases per 100,000 person-years in those without recent weight loss.
This works out as a 57 percent higher risk.
Cancer of the esophagus, stomach, liver, biliary tract, or pancreas were particularly common in participants with recent weight loss.
There were 173 cases of those types of cancers per 100,000 person-years for those who had lost more than 10 percent of their body weight, compared to 36 cancer cases per 100,000 person-years for those with no recent weight loss.
The researchers found that many other cancer types, including breast, genital, urinary, brain and melanoma, were not associated with recent weight loss.
Participants with recent weight loss had a higher risk of subsequent cancer diagnosis when they were not intending to lose weight, but happened to be doing more exercise and eating more healthily.
According to the American Cancer Society, unexplained weight loss is often the first noticeable symptom of cancers of the esophagus, pancreas, stomach and lung.
The researchers also noted that many conditions, as well as cancer, can cause weight loss.
Their findings are at odds which much of the existing literature.
A 2023 study of almost 600,000 people found that every five-point increase in body mass index (BMI) is linked to an 11 per cent higher risk of obesity-related cancer, even in people without cardiovascular disease or type 2 diabetes.
A large study published last year by researchers from Newcastle University in the UK found that limiting fast food helps to lower your risk of some types of cancer.
Fast food is associated with cancer because eating it in large amounts makes you more likely to be overweight. Excess weight can trigger a host of hormonal changes that can cause tumors to grow.
A German study in 2022 found that being overweight or obese at any point in life can increase a person’s risk of developing colorectal cancer down the line, and the longer a person is overweight the more the risk builds.
Another study by the American Cancer Society found that being overweight or obese is the second most common cause of cancer after smoking.
It found that carrying excess fat, particularly around the tummy, is directly linked to 13 different cancers, including post-menopausal breast cancer, colorectal and endometrial cancer.