Obesity increases the risk of developing several types of cancer. This knowledge has been consolidated in recent years by several epidemiological studies. But unlike other factors, such as smoking, most people and even doctors are not aware of the relationship. Unraveling how excessive fat contributes to tumor genesis can help in prevention and in the creation of new drugs.
More than 200 varieties of cancer are already known and, so far, science has discovered the link between obesity and 13 types of the disease, such as those of the liver, thyroid, ovary, kidney, pancreas, stomach, esophagus and gallbladder. Also on the list are cancers of the tissue surrounding the brain and spinal cord (meningioma), blood cancer (multiple myeloma), colorectal cancer, breast cancer (postmenopausal) and endometrial cancer (tissue that lines the uterus). .
The concern raised by the relationship between obesity (on the rise in the world) and the disease has led institutions such as the World Health Organization (WHO), the National Cancer Institute (NCI), in the United States, and the National Cancer Institute (Inca). ), in Brazil, to alert to the need for prevention.
With the drop in the number of smokers, the tendency is for obesity to become the most relevant preventable factor in the genesis of cancer, according to the American Society of Clinical Oncology (Asco).
A study published this month in the journal Nature Communications offers a new explanation for putting this puzzle together. According to the work, cellular adaptation to obesity is governed by palmitic acid, derived from fat.
This adaptation produces changes in stem cells that, instead of originating healthy tissues, become carcinogenic. The study was performed with cell culture of breast tumors from 223 patients. “Obese people are more likely to develop cancer, and when they do, the tumors appear to be more aggressive,” says Nils Halberg of the University of Bergen in Norway, one of the authors. “This new understanding could lead to better, targeted treatments for obese cancer patients.”
“There is no doubt that obesity increases the risk of several types of cancer”, says physician Paulo Hoff, president of the Brazilian Society of Clinical Oncology (SBOC). “What’s happening now, as this Nature Communications paper demonstrates, is a refinement of the hypotheses,” he says.
The first retrospective surveys (when researchers gather information about the risk factors patients were exposed to) found that obese postmenopausal women had a higher risk of developing breast cancer. Then other studies showed a relationship with liver cancer. In recent years, oncologists have observed an increase in cases in which these tumors are not caused by alcohol use or viral hepatitis – but by the accumulation of fat (steatosis) in the liver.
The reasons
“There are still mechanisms that need to be clarified”, says breast specialist Renato Cagnacci, from the AC Camargo Cancer Center. But at least three reasons that can explain why excess fat increases the risk of developing malignant cells are well established.
Obesity raises the amount of insulin in the body, a hormone that increases metabolism and cell duplication, something that can trigger tumors. Fat tissue also produces female hormones (estrogen and progesterone), a risk factor for the development of breast cancer, especially in obese postmenopausal women.
The third important factor is chronic inflammation. Obesity triggers the production of some cytokines (proteins excreted by cells) that leave the person in a permanent inflammatory state, something that increases the risk of cancer. “The WHO estimates that about 20% of all cancers are related to obesity,” says Cagnacci.
Despite the evidence accumulated in recent years, ignorance about the subject persists. “Most doctors still tend not to see obesity as a risk factor for cancer,” says oncologist Hoff. “That needs to change.”
Prevention
Obesity also appears to increase the risk of tumor recurrence. Epidemiological studies indicate that women who are obese or who gain weight after treatment face a higher risk of the disease returning. The explanation lies, again, on high estrogen levels. “We always advise patients undergoing treatment to maintain a healthy lifestyle, lose weight and do physical activity,” says Cagnacci.
With that goal in mind, artisan Leila Maria de Siqueira Garcia, 64, reorganized her habits. She was never thin, but she weighed over 130 kg during breast cancer treatment. “One day I looked at myself in the mirror and decided that I would get a new body,” she said. She lost 47 kg in three years. “On my own, I changed my diet to reduce fat, sugar and soda,” says she, who was discharged from cancer treatment more than 10 years ago. “Today I feel great, but I want to lose another 5 kg to have breast reconstruction surgery,” she says.
limitations
Most of the evidence linking obesity to an increased risk of cancer is derived from large cohort studies, a type of observational study that aims to analyze, in a previously defined population, what the incidence of a given disease will be. Data from observational studies can be difficult to interpret. Despite these limitations, there is consistent evidence that large amounts of body fat increase the risk of cancer, according to the NCI of the United States.
In 2016, the WHO’s International Agency for Research on Cancer (IARC) analyzed evidence from more than a thousand studies on the topic and concluded that the absence of excess body fat reduces the risk of cancer. The work was published in The New England Journal of Medicine.
“Cancer is a multifactorial disease. It is difficult to define the cause in a particular person”, said oncologist Ronaldo Corrêa, from the Inca Prevention and Surveillance Coordination. “In almost 90% of cases, the triggering factor is a lifestyle behavior or environmental exposure.”
According to Corrêa, there is no study that has evaluated the relative risk of being overweight in the Brazilian population. The researcher explains that many of the surveys carried out in the world do not analyze only the obesity ranges.
They include all sorts of excess in the same package. That is: one category of overweight and three of obesity, according to the classification of BMI (body mass index).
This definition of overweight contributed to the emergence of 1.8% of cancer cases in Brazil, according to an estimate published by Corrêa and colleagues last year in the scientific journal PLOS 1. According to Inca, 5% of breast cancer cases in post-menopause are attributable to excess body fat.
“It is not uncommon for three institutions to report different values”, says Corrêa. “It depends on the data from the population surveys the researchers used.”
little tire
Paulo Hoff points out: “What increases the risk of cancer is obesity (BMI above 30), not a little overweight”, he says. “If a person has a spare tire, it does not mean that they have an increased risk of suffering from the disease.”
The trend is that in the coming years the number of cancer cases attributable to excess fat will increase.
The advance of overweight, which already affects 57.5% of Brazilians, causes concern, because the tendency is that they continue to gain weight and become obese. It is more difficult to make an overweight person lose weight than it is to prevent a person of normal weight from turning into someone who is overweight.
“Adopting a healthy lifestyle as a protective factor is a simple thing that most people can pursue and achieve,” says breast specialist Cagnacci.
The value of the benefits is immense. The information is from the newspaper. The State of São Paulo.
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