Science is already explaining the link between cancer and obesity

Posted 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, such as smoking, most people and even doctors are not aware of the relationship. Uncovering 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, breast cancer (postmenopausal), and cancer of the endometrium (the tissue that lines the uterus).

The concern raised by the relationship between obesity (on the rise in the world) 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 alert the need for prevention.

With the number of smokers declining, the trend 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 It offers a fresh explanation to put this puzzle together. According to the work, cellular adaptation to obesity is subject to lipid-derived palmitic acid.

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. “People who are obese are more likely to develop cancer, and when that happens, tumors appear 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 paper explains, is a revision of hypotheses,” he says.

The first retrospective surveys (when researchers collected information about patients’ 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 caused not by alcohol abuse or viral hepatitis – but by a buildup of fat (steatosis) in the liver.

the reasons

“There are still mechanisms that need 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 raises the amount of insulin in the body, a hormone that increases metabolism and cell multiplication, something that 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) that leave a person in a permanent inflammatory state, increasing the risk of cancer. “The World Health Organization estimates that about 20% of all cancers are related to obesity,” Kagnashi says.

Despite the evidence accumulating in recent years, ignorance of the topic persists. “Most clinicians still tend not to consider obesity as a risk factor for cancer,” says Hof, an oncologist. “This needs to change.”

protection

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 the high estrogen levels. “We always advise patients undergoing treatment to maintain a healthy lifestyle, lose weight and be physically active,” Kagnashi says.

With this goal in mind, artist Leila Maria de Sequeira Garcia, 64, reorganized her habits. She was never skinny, but she weighed more than 130 kg during the treatment of breast cancer. “One day I looked at myself 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 cut back on fat, sugar, and soda,” she says, who came out of 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.

determinants

Most of the evidence linking obesity with an increased risk of cancer derives from large cohort studies, the type of observational study that aims to analyze the incidence of a particular disease in a pre-specified population. It can be difficult to interpret data from observational studies. Despite these limitations, there is consistent evidence that large amounts of body fat increase the risk of cancer, according to the US National Cancer Institute.

In 2016, the International Agency for Research on Cancer (IARC) of the World Health Organization analyzed the evidence from more than a thousand studies on the topic and concluded that having no 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 determine the cause in a particular person,” said oncologist Ronaldo Corre of the Inca Organization for Prevention and Control. “In approximately 90% of cases, the causative agent is lifestyle behavior or environmental exposure.”

According to Corrêa, there is no study that has assessed the relative risk of being overweight in a Brazilian population. The researcher explains that many surveys conducted in the world do not only analyze the ranges of obesity.

They include all kinds of surplus in the same package. They are: one category of overweight and three categories of obesity, as classified by body mass index (BMI).

This definition of excess weight contributed to 1.8% of cancer cases in Brazil, according to an estimate published last year by Correa and 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 is not uncommon for three institutions to report different values,” Correa says. “It is based on data from the population surveys that the researchers used.”

small tires

“What increases the risk of cancer is obesity (a BMI above 30), not just being a bit overweight,” Paulo Hoff points out. “If a person has a spare tire, it does not mean that they are at 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 progression of excess weight, which already affects 57.5% of Brazilians, is cause for concern, because the tendency is that they continue to gain weight and become obese. Getting an overweight person to lose weight is more difficult than preventing a person of normal weight from turning into an overweight person.

“Adopting a healthy lifestyle as a preventative factor is a simple thing that most people can strive for and achieve,” says breast specialist Kagnashi.

The value of the benefits is enormous. Information from the newspaper. State of Sao Paulo.