Losing weight lowers cancer risk, study says

A large, new study found that people who had significant weight loss thanks to bariatric surgery gained a remarkable benefit: Their likelihood of developing cancer dropped sharply.

Published June 3 in the medical journal JAMA, the study followed more than 30,000 obese adults for nearly a decade. Those who had weight loss surgery were found to have a 32% lower risk of developing cancer and a 48% lower risk of dying from cancer, compared to a similar group of people who did not have the surgery.

Over the period covered by the study, people who had weight loss surgery lost an average of 25 pounds more than others. Scientists found that the more weight was lost, the more the risk of cancer was reduced.

Obesity is an important cancer risk factor. Health officials link being overweight to higher rates of many types of cancer. The new study is one of the largest and most rigorous to suggest that the increased risk can be reversed in people who lose substantial amounts of weight.

The research focused on weight loss through bariatric surgery, but its authors speculated that the benefit would also apply to weight loss achieved through other methods, such as diet and exercise or the use of medication. Steven E. Nissen, a co-author of the study, said the findings “offer yet another reason why obese people should lose weight.”

“This is an important public health message,” said Nissen, academic director of the Heart, Vascular and Thoracic Institute at the Cleveland Clinic. “I think a lot of the public isn’t aware or doesn’t understand that obesity is such a huge risk factor for cancer and they certainly don’t understand that this risk is reversible.”

An expert not involved in the study, Ania Jastreboff, said the study demonstrates that treating obesity and achieving “clinically significant” weight reductions can improve patients’ health outcomes. “It’s a really important finding,” said she, who is a professor at the Yale School of Medicine and director of weight management and obesity prevention at the Yale Stress Center.

According to the US Centers for Disease Control and Prevention (CDC), obesity is a major cause of preventable cancers, alongside smoking, heavy alcoholism and exposure to ultraviolet radiation.

People who are overweight or obese are at increased risk of developing 13 different types of cancer, including endometrial, breast, kidney, liver, esophageal and colorectal cancer. The CDC estimates that the 13 cancers linked to obesity make up 40% of all cancers diagnosed annually in the United States.

It’s not entirely clear why obesity appears to promote cancer, but one potential factor is inflammation. Studies reveal that fat cells release into the blood stream a series of inflammatory proteins known as cytokines, which have been found to stimulate cancer cells.

Many scientists think that this state of chronic inflammation caused by fat cells is also one of the reasons why people with obesity have higher rates of complications from Covid-19.

Fat cells are often seen as being inert — “just sitting around doing nothing,” Nissen said. “In reality, however, they are metabolically active. We think that the chronic inflammation produced by obesity, by these very metabolically active fat cells, is one of the cancer-inducing mechanisms.”

According to the CDC, people with obesity tend to have higher levels of hormones such as insulin or insulin-like growth factor 1, or IGF-1, which can stimulate the development of colon, kidney, and prostate cancers. and endometrium.

Bariatric surgery can lead to substantial weight loss. Although some patients eventually regain some of their lost weight, studies show that most people who have bariatric surgery are able to maintain a reduction of more than 20% in their weight a decade after the procedure.

That’s a lot more than people with obesity can normally lose and maintain with diet and exercise alone.

For the new study, Nissen and his colleagues wanted to see how much weight loss would affect cancer rates.

They recruited 5,053 obese people who had had bariatric surgery at the Cleveland Clinic and followed them up. Each patient was compared to five other patients who were similar in many respects. They were roughly the same age, sex and race, similar medical histories and body mass indices, but had not had weight loss surgery.

The study involved more than 30,000 participants, of which 25,265 were part of the control group. Patients in both groups had a mean age of 46 years and a BMI of 45, classified by the CDC as severely obese. This equates to a person 1.72 m tall and 136 kg.

According to the CDC, people with a BMI between 25 and 30 are considered overweight and those with a BMI greater than 30 are classified as obese. A large national study published last year found that 42% of adults in the US are obese and about 9% are severely obese.

Not all people with obesity can have weight loss surgery. To qualify for this, patients generally must have a BMI of at least 40, or a BMI of 35 or more associated with a condition linked to obesity, such as type 2 diabetes, hypertension, or heart disease. In the new study, people who had the surgery had either had gastric bypass or sleeve gastrectomy procedures.

After a decade, patients who had the surgery had lost an average of 28 kg, while those in the control group (advised by their doctors to try to lose weight on their own) had lost an average of 2.7 kg.

Just under 3% of patients who had surgery had developed cancer, compared with 4.9% of patients in the non-operated group — equivalent to a 32% reduction in risk for those who had bariatric surgery.

Overall, the data suggested that patients needed to lose a large amount of weight, at least 20% to 25% of their body mass, to see a beneficial change in their cancer risk, said Dr. Ali Aminian, lead author of the study and director of the Cleveland Clinic’s Bariatric and Metabolic Institute.

Risk reduction was especially important for endometrial cancer, the cancer most strongly associated with obesity.

Aminian and several of the study’s authors reported receiving research grants or consulting fees from Medtronic, a company that makes devices used in weight-loss surgery. Nissen revealed that she has received research funding from companies that develop weight loss drugs, including Novartis and Eli Lilly.

Nissen said that while the new study focused on bariatric surgery, the message is that people should aim to lose weight in whatever way they can, whether that’s with diet and exercise or with medication assistance. About 250,000 people a year have bariatric surgery in the US, Nissan said, “but there must be 100 million obese people.”

“We can’t do bariatric surgery on a third of the country’s population,” he commented. “It’s just not feasible.”

Obesity is often portrayed as a result of a lack of willpower. But Ania Jastreboff, from Yale, pointed out that since 2013 the American Medical Association has recognized obesity as a chronic disease. She pointed out that, as is the case with any other chronic disease, people with obesity should not think they have to face the problem alone. They should seek help from a physician or other health care professional who can provide them with safe and effective treatments.

“When a patient comes to me to talk about obesity, one of the first things I say is that it’s not your fault, it’s not your choice,” she said. “We shouldn’t blame patients for having the disease of obesity any more than we blame patients for having diabetes or hypertension.”

Translation by Clara Allain