Published on 01/30/2022 20:00
Obesity increases the risk of many types of cancer. This knowledge has been reinforced in recent years by several epidemiological studies. But unlike other factors, like smoking, most people and even doctors aren’t aware of the relationship. Finding out how excess fat contributes to tumor formation can help prevent and develop new drugs.
More than 200 types of cancers are already known, and so far science has discovered the link between obesity and 13 types of diseases, such as diseases of the liver, thyroid, ovaries, kidneys, pancreas, stomach, esophagus and gallbladder. The list also includes cancers of the tissues surrounding the brain and spinal cord (meningioma), leukemia (multiple myeloma), colorectal cancer, cancer of the breast (postmenopause), and cancer of the endometrium (the tissue that lines the ‘uterus).
Concern over the relationship between obesity (increasing worldwide) and disease has led to the emergence of 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 warn of the need for prevention.
With the decline in the number of smokers, obesity tends to become the most important 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 Communication It offers a new explanation for putting this puzzle together. According to the work, cellular adaptation to obesity is subject to palmitic acid derived from lipids.
This adaptation results in changes in stem cells that become carcinogenic rather than forming healthy tissue. The study was conducted by transplanting breast tumor cells into 223 patients. “Obese people are more likely to develop cancer, and when this happens the tumors seem to be more aggressive,” says Nils Hallberg of the University of Bergen in Norway, one of the authors. “This new understanding could lead to better targeted therapies for obese cancer patients.”
“There is no doubt that obesity increases the risk of several types of cancer,” says Dr. Paulo Hoff, president of the Brazilian Society of Clinical Oncology (SBOC). “What is happening now, as the Nature Communications article explains, is a revision of assumptions,” he says.
Early retrospective surveys (when researchers collected information about patient risk factors) found that obese postmenopausal women had a higher risk of developing breast cancer. Then other studies showed an association with liver cancer. In recent years, oncologists have noticed an increase in cases where these tumors are not caused by alcohol abuse or viral hepatitis, but by an accumulation of fat (steatosis) in the liver.
“There are still mechanisms to be elucidated,” says breast specialist Renato Cagnacci, MD, of the Camargo AC Cancer Center. But there are at least three reasons why excess fat increases the risk of developing malignant cells.
Obesity increases the amount of insulin in the body, a hormone that increases metabolism and cell multiplication, which can lead to tumors. Adipose tissue also produces female hormones (estrogen and progesterone), which are a risk factor for breast cancer, especially in obese postmenopausal women.
The third important factor is chronic inflammation. Obesity leads to the production of certain cytokines (proteins secreted by cells) which leave a person in a permanent inflammatory state, increasing the risk of cancer. “The World Health Organization estimates that around 20% of all cancers are linked to obesity,” says Kagnashi.
Despite the evidence accumulated in recent years, ignorance of the subject persists. “Most clinicians still tend not to consider obesity as a risk factor for cancer,” says Hof, an oncologist. “That has to change.”
Obesity also appears to increase the risk of tumor recurrence. Epidemiological studies suggest that women who are obese or who gain weight after treatment have a higher risk of recurrence. The explanation, again, lies in high estrogen levels. “We always advise patients undergoing treatment to maintain a healthy lifestyle, lose weight and be physically active,” says Kagnashi.
To this end, the artist Leila Maria de Sequeira Garcia, 64, has reorganized her habits. She was never skinny, but she weighed over 130 kg during treatment for breast cancer. “One day I looked in the mirror and decided to conquer a new body,” he said. Lost 47 kg in three years. “On my own, I changed my diet to reduce fat, sugar and soda,” says she, who emerged from cancer treatment more than 10 years ago. “Today I feel better, but I want to lose another 5 kg for breast reconstruction surgery,” she says.
Most of the evidence linking obesity to an increased risk of cancer comes from large cohort studies, the type of observational study that aims to analyze the incidence of a particular disease in a predefined population. Data from observational studies can be difficult to interpret. Despite these limitations, there is consistent evidence that high amounts of body fat increase cancer risk, according to the US National Cancer Institute.
In 2016, the World Health Organization’s International Agency for Research on Cancer (IARC) analyzed evidence from more than a thousand studies on the subject and concluded that the absence of excess fat body 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 determine the cause in a specific person,” said oncologist Ronaldo Corre of the Inca Organization for Prevention and Control. “In about 90% of cases, the causative agent is lifestyle behavior or environmental exposure.”
According to Corrêa, no study has evaluated the relative risk of being overweight in a Brazilian population. The researcher explains that many surveys conducted around the world do not only analyze obesity ranges.
They include all kinds of extras in the same package. They are: one category of overweight and three categories of obesity, classified by body mass index (BMI).
This definition of excess weight has contributed to 1.8% of cancer cases in Brazil, according to an estimate published last year by Correa and his colleagues in the scientific journal PLOS 1. According to the Inca, 5% of Postmenopausal breast cancer cases are attributable to excess fat. . In the body.
“It’s not uncommon for three institutions to report different values,” says Correa. “It’s based on population survey data that the researchers used.”
“What increases the risk of cancer is obesity (a BMI greater than 30), not just being slightly overweight,” said Paulo Hoff. “If a person has a spare wheel, it does not mean that he is at 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 increase in overweight, which already affects 57.5% of Brazilians, is worrying, since the trend is that they continue to gain weight and become obese. Getting an overweight person to lose weight is more difficult than preventing a normal weight person from becoming an overweight person.
“Adopting a healthy lifestyle as a preventative factor is a simple thing that most people can strive for,” says breast specialist Kagnashi.
The value of benefits is enormous. Log information. State of Sao Paulo.