Smoking has been the leading preventable cause of cancer for decades and still kills more than 500,000 people a year in the United States. But obesity is about to take the lead, as Americans' waistlines continue to widen as smoking falls.
The change could occur within five to ten years, said Otis Brawley, a Johns Hopkins oncologist and former Chief Medical Officer of the American Cancer Society. Rising rates of obesity could threaten the steady decline in cancer mortality rates since the early 1990s, he said.
Yet only about half of Americans are aware of the link between being overweight and cancer. And researchers struggle to answer fundamental questions such as: how does excess weight increase the risk of contracting the disease and if, on the contrary, losing weight helps prevent cancer or recurrence? .
Obesity and overweight – long implicated in heart disease and diabetes – have been associated in recent years with an increased risk of developing at least 13 types of cancer, including malignant tumors of the stomach, pancreas, colorectal and liver, as well as postmenopausal breast cancer. Researchers at the American Cancer Society claim that excess weight is linked to about 8% of all cancers in the United States and about 7% of cancer deaths.
Compared to people of normal weight, obese patients are more likely to have their cancer return and have a lower probability of survival. Perhaps the most alarming are young people who, as a group, are heavier than their parents, develop weight-related malignancies, including colorectal cancer, at an earlier age than previous generations, experts say .
"A complex interaction"
The precise link between cancer and excess weight is not known, but researchers focus on the "visceral" fat that surrounds internal organs. Rather than being a harmless glob, this fat is a "metabolically active organ" that produces hormones such as estrogen, associated with a higher risk of breast cancer and some other cancers, according to the report. American Institute for Cancer Research, a non-profit group that: focuses on food, nutrition and cancer.
The fat also secretes proteins that cause higher insulin levels, which can stimulate cell growth and increase the risk of cancer. And this can cause chronic inflammation, another risk factor for the disease, depending on the group.
"It's a complex mixture of metabolism, inflammation and immunity," said Jennifer Ligibel, a breast oncologist at the Dana-Farber Cancer Institute. "It creates a more permissive environment for cancer."
About 7 out of 10 Americans are overweight or obese, according to a 2015 article in JAMA Internal Medicine. People are considered overweight if they have a body mass index (BMI) of 25 to 29 years and are obese if they have a BMI of 30 or more.
The proportion of overweight adults has remained relatively stable over the last few decades, but the rate of obesity has skyrocketed. In the early 1960s, almost 11% of men and nearly 16% of women were obese; in 2016, these percentages were 38% and 41%, respectively, according to the cancer society.
The risk of cancer increases with being overweight. "It seems that the more obese you are, the greater the risk," said Jonathan Wright, urologist at the Seattle-based Fred Hutchinson Cancer Research Center. There is a link between overweight and cancer, "but it's not as strong," he said.
The type of cancer most associated with obesity is the endometrium, which develops in the uterine lining. Obese and overweight women are two to four times more likely to develop the disease than women of normal weight, and the risk increases with weight gain, according to the National Institutes of Health.
According to the NIH, people who are overweight or obese are twice as likely to develop liver and kidney cancer and about 1.5 times more likely to develop pancreatic cancer than people of normal weight.
In addition, having too much abdominal fat – a larger waistline – is linked to an increased risk of colorectal cancer and some other cancers, regardless of their weight, the company said.
Several researchers are currently conducting clinical trials to try to prove what many already think: losing weight reduces the risk of cancer or recurrence. Some clues suggest that they may be right – seriously obese people who undergo bariatric surgery, for example, decrease their risk of developing cancer – but additional data is needed.
Essays and studies
Carol Massey, who is 59 years old and was treated for breast cancer two years ago, is enrolled in a national trial to determine whether weight loss makes breast cancer return less likely. She has reduced her caloric intake, intensified her exercises and regularly consulted a health coach based at the Boston Dana-Farber Cancer Institute, which runs the BWEL study on breast cancer weight loss.
To be eligible for the test, women must have a BMI of 27 or higher. The study, which will include about 3,100 women, will compare the Massey group – which receives weight loss and health education materials – to a group that only receives teaching materials.
Massey, who lives in Paola, Kan, said she had come to look forward to her coach's calls, which were initially once a week. "We have to be friends, she would ask about my family," she said. "One time, she even phoned me while she was on vacation in Cabo San Lucas" in Mexico.
Over time, the 5-foot-8 Massey lost 30 pounds. She now weighs 150 pounds.
These are the results that Ligibel, the principal investigator, hopes to achieve. If the study shows that weight loss is associated with a reduction in recurrences, doctors might prescribe a weight loss program as a standard treatment for breast cancer patients – just like rehabilitation. heart is recommended for patients with a heart attack. This could pave the way for insurance coverage.
Gail Folloder joined a 16-week program at the MD Anderson Cancer Center at the University of Texas for heavier women at high risk of breast cancer because both parents had a cancer and she wanted to prevent it. A 67-year-old Houston resident underwent a "hunger training", which uses continuous blood glucose monitoring to show participants when they need fuel and urges them to limit their diet at these times.
"The idea is to help people learn to eat only when they are really hungry," said Karen Basen-Engquist, a behavioral scientist at the cancer center. "We eat for all kinds of reasons – sometimes because we are with other people or because we are bored or stressed."
It worked for Folloder. "I used to say that I was hungry all the time, but that was really not the case," she says. "Now, I'm more in tune with my body."
In addition to talking to a weekly dietitian, she intensified her physical activity using a hoop and exercise bike. Folloder, who is 5 feet 9 years old, has gone from 219 pounds to 191 pounds.
The women in the Folloder group will be compared to a "control" group that participates in a weight loss program but does not monitor blood glucose. The results are expected this year.
Fred Hutchinson's Wright focuses on overweight and obese men with low-grade, slow-growing prostate cancer who have decided to adopt an "active surveillance" approach – which involves monitoring via blood tests, physical exams and biopsies – rather than treatments such as radiation therapy. or surgery. He is investigating whether controlling patients' blood glucose levels through weight loss will prevent cancer from getting worse and improve survival. The goal is that participants lose 7% of their body weight.
The study is based on the Diabetes Prevention Program, which has shown that people at high risk of type 2 diabetes can prevent or delay the disease by losing a modest weight due to dietary and other changes. increased physical activity
Find the right diet
Steve Borden, 57, participated in the November 2001 test called Lifestyle Prostate Cancer Active Lifestyle, which had been assigned to a nutritionist and an exercise physiologist to teach him how to diet. and to exercise.
The 5 foot 10 inch Borden has lost 30 pounds and now weighs 198 pounds. It only targets 1,800 calories a day. He regularly uses the treadmill and raises weights. He said that a recent test had shown that his PSA – for prostate-specific antigen, which, when it is high, may indicate a cancer – has gone down slightly, although his doctors do not know if this is related to her weight loss.
In general, how much do you need to lose to improve your chances of cancer? Dana-Farber's Ligibel said it was not clear, but that data suggests that a 5% reduction in body weight would have a beneficial impact on blood sugar and inflammation.
According to experts, it is important to avoid any weight gain for those who wish to reduce their risk of cancer. Brawley of Johns Hopkins said that the goal should be to maintain an "energy balance" – not consuming more calories than is burned by exercise and other activities.
Nutritionists say the key is to reduce portion sizes, avoid sugar, and favor meals rich in vegetables, fruits, whole grains and beans, and reduced animal protein.
Anthony Perre, head of outpatient medicine at the American Cancer Treatment Centers, said that the Mediterranean diet – which focuses on plant-based foods, whole grains and lambs. Olive oil – has been associated with improving cancer outcomes.
"But the right diet is the one you can maintain in the long run," he said. "Whether it's Atkins, low in carbohydrates or calories, they all work if you stay with them."