Why Being Overweight Increases Your Risk of Cancer

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Researchers in several new studies say there’s more evidence that obesity can raise a person’s risk of more than dozen different types of cancer.

When Dr. Ghassan Abou-Alfa began focusing on finding new treatments for liver cancer two decades ago, his fellow physicians weren’t ready to acknowledge the link between cancer and obesity.

“In my own practice, if I said 15 years ago that obesity is the cause of your cancer, it was considered far off, even among many of my colleagues,” said Abou-Alfa, a renowned oncologist and cancer researcher at Memorial Sloan-Kettering Cancer Center in New York.

But research on the links between obesity and cancer has come a long way since then.

“The evidence now shows that patients with morbid obesity and diabetes are potentially prone to get non-alcohol-related fatty liver disease that can lead to liver cancer,” Abou-Alfa told Healthline.

With this being Liver Cancer Awareness Month, it’s an opportune time, he said, to tell the public that obesity-related liver cancer is increasing.

“While hepatitis B–related liver cancer in the U.S. is on the decline, obesity-related liver cancer is on the rise. There is no doubt about this,” Abou-Alfa said.

Cancer and obesity links

And as Abou-Alfa noted, it’s not just liver cancer.

The Centers for Disease Control and Prevention (CDC) announced this month that being overweight or obese in fact increases a person’s risk for at least 13 different types of cancerTrusted Source.

The cancers include those of the liver, brain, esophagus, thyroid, gallbladder, stomach, pancreas, kidney, uterus, and colon.

They make up 40 percent of all diagnosed cancers in the United States, according to the report.

CDC researchers found that in 2014 alone, more than 630,000 Americans had a type of cancer that was associated with being overweight or obese.

These cases amounted to more than 55 percent of all cancers diagnosed among women and 24 percent of all cancers diagnosed among men in the United States.

Diabetes, heart disease, and cancer

While it’s been common knowledge for decades that being overweight is a factor in diabetes and heart disease, obesity’s deepening links to cancer are still being discovered.

In a press conference on Oct. 3, Dr. Anne Schuchat, deputy director of the CDC, acknowledged that the “awareness of some cancers being associated with obesity and [being] overweight is not yet widespread” among Americans.

The CDC noted in its report that the International Agency for Research on Cancer, the cancer wing of the World Health Organization (WHO), says that there is “sufficient evidence” to link excess body fat to at least 13 different cancers.

The related issue, of course, is the prevalence of obesityTrusted Source, a chronic disease affecting more than 1 in 3 adults in the United States.

The CDC also announced this month that obesity rates among American adults has increased from just over 30 percent in 2000 to nearly 40 percent in 2016.

The report, which comes from the CDC’s National Center for Health Statistics, measures obesity according to body mass index.

This is a rough measure of fatness that takes a person’s weight and divides it by their height squared.

Research for decades

Finding the connections between a higher body weight and certain cancers is a booming field of research.

But the public is just coming up to speed, experts acknowledge.

A study in 2003 published in The New England Journal of Medicine linked obesity to cancer death among American adults.

More recently, the American Society of Clinical Oncology (ASCO) concluded in 2014 that obesity has surpassed smoking as the leading preventable cause of cancer.

Dr. Caroline Apovian, president-elect of the Obesity Society and a world leader in the field of weight loss, said the society has delved into the links between obesity and cancer and prepared a paper that will be published in the next month.

She said that while the public’s understanding of cancer’s link to obesity isn’t as high as the awareness of obesity’s link to various other diseases, the public is now discovering the studies.

“The research didn’t just appear overnight,” said Apovian, who’s also a best-selling author, professor, and director of clinical research at the Obesity Research Center, Boston University Medical Center.

Apovian joined the Obesity Society to continue the organization’s vision to understand, prevent, and treat obesity and improve lives through research, education, and advocacy.

She told Healthline the growing amount of research on obesity and cancer, including the latest study from the CDC, highlights the need for the national medical community to deepen its commitment to nutrition and diet.

And while it’s important to bring oncologists into the nutrition conversation, she said it’s “even more fundamentally important” to get to the patients before the cancer develops.

“The Obesity Society is focusing on primary care physicians first,” she explained. “Seeing the patient years before they develop the cancer, that’s where it needs to start.”

Apovian added that oncologists need to counsel on diet and exercise as well, “but if you don’t start with primary care, we’re never going to decrease the rates of cancers.”

Inflammation, inflammation, inflammation

Why is obesity causing more cancer?

Apovian and other experts tell Healthline that a lot of it has to do with the fact that extra fat in the body can easily boost levels of inflammation, which is also increasingly linked to cancer.

Apovian said the person who “goes to Cheesecake Factory and eats for two hours, consuming 2,000 calories of sugar and fat, if they do it enough, they are creating toxins in their body, and their body is going to react. The result is inflammation as well as hormonal changes.”

Being overweight may also increase levels of various hormones, she said, including sex hormones and insulin, and also generate insulin-like growth factor, which plays a role in growth and has been linked to cancer risk.

Sugar’s link to cancer

While there is an ongoing debate in science over whether or not sugar feeds cancer and causes tumors to grow, scientists in Belgium revealed a breakthrough last week that suggests that sugar awakens cancer cells.

The researchers, who published the findingsTrusted Source of their nine-year study in the journal Nature Communications, focused on the Warburg effect, which is the observation that tumors convert much higher amounts of sugar into lactate compared to healthy tissues.

This activity in the body has been extensively studied and even used to detect tumors, but until this study, it has been uncertain whether the effect is merely a symptom of cancer or an actual cause.

The scientists believe sugar produces more of the most common cancer-causing genes, also known as Ras proteins, which fuels aggressive tumors.

In other words, sugar “awakens” existing cancer cells, the researchers say.

In a statement, co-author Johan Thevelein said “Our research reveals how the hyperactive sugar consumption of cancerous cells leads to a vicious cycle of continued stimulation of cancer development and growth.”

Thevelein concluded that the study could once and for all explain the correlation between the strength of the Warburg effect and tumor aggressiveness.

“This link between sugar and cancer has sweeping consequences,” he said.

The Belgium study finding could in fact lead to new treatments and new diets for a variety of cancers.

“The next step is to find out whether these results also apply to patients,” Thevelein said. “To do this, clinical trials with oncologists have to be developed. Only after these results from these kind of trials are known, statements can be made about possible consequences for cancer treatments and adjusted diets.”

Thevelein, a molecular biologist at Katholieke Universiteit Leuven in Belgium, did state this caveat last week: “Some people are interpreting that we have found a mechanism for how sugar causes cancer, but that is certainly not the case.”

Instead, Thevelein said, his work shows just how sugar is broken down differently in cancer cells.

There are already a handful of studies in humans that have shown a demonstrable connection between lower-sugar diets and a lower rate of cancer recurrence, especially for people who are obese, experts tell Healthline.

Thevelein’s work adds to that research, and he said his findings could indeed mean that people with cancer should eat a low-sugar diet.

New administration and the sugar industry

Thevelein’s study could be a clarion call to oncologists as well as cancer patients to pay even closer attention to nutrition.

But efforts by physicians, organizations like the Obesity Society, and various medical and health lobbying groups to promote nutrition could be hampered by a presidential administration that critics say has embraced corporate interests, dismissed nutritional programs in schools, and more.

As Healthline reported in August, Dr. Brenda Fitzgerald, the new director of the CDC, took $1 million from Coca-Cola when she ran Georgia’s public health department to fund a childhood obesity campaign.

Fitzgerald was accused by many public health experts of downplaying and even at times ignoring the nutrition aspects of the campaign and focusing only on the exercise part.

Most nutriti0n experts now say that while exercise is an important part of staying healthy and fighting obesity, diet and nutrition are the most important components.

While Fitzgerald denied that she ever downplayed nutrition in favor of exercise after Coca-Cola’s $1 million gift, she didn’t directly address the issue when commenting to Healthline in August.

Multiple studies, including several conducted by the CDC, have concluded that sugar-filled beverages such as Coke are a significant contributor to childhood obesity, heart disease, and type 2 diabetes.

The CDC’s websiteTrusted Source says, “Frequently drinking sugar-sweetened beverages is associated with weight gain/obesity, type 2 diabetes, heart disease, kidney diseases, nonalcoholic liver disease, tooth decay and cavities, and gout, a type of arthritis.”

The CDC sent Healthline a statement by Fitzgerald addressing whether she would accept future funding from Coca-Cola or other corporations for any CDC program.

“Where there’s science to support public health measures, I am a champion for those efforts. For public-private partnerships, I believe that finding common ground and voluntarily working together has been successful and sustainable,” she said in the statement.

As CDC director, she continued, “I am committed to evidence-based recommendations and education, including those that support healthy nutrition.”

Fitzgerald told The New York Times she would consider allowing Coca-Cola to fund the federal agency’s programs.

“I will continue the review process in place at CDC,” Fitzgerald wrote to the newspaper, “and any offers of support would be considered through this process before moving forward.”

Obesity and breast cancer

Meanwhile, research is also showing an increasing link between obesity and breast cancer.

In a recent study, The Ohio State University Comprehensive Cancer Center (OSUCCC) was among the first to show that obesity alters genes involved in inflammatory response (32 genes), hereditary disorders (48 genes), and other immunological diseases (42 genes).

A team of researchers looked at gene expression analysis of tissue samples collected from 121 women with no history of breast cancer.

All women participating in the study were undergoing breast reduction, and 51 participants were considered clinically obese.

The team examined the obesity and inflammation response, finding 308 genes important in the process.

Of those 308 genes, 240 were more likely to have sporadic mutations and low gene expression in obese women while 68 genes were shown to have a decreased risk for gene mutations and high gene expression.

All of the participants’ affected genes were involved in diseases and disorders for inflammatory response, hereditary disorder, and immunological disease.

Dr. Peter Shields, senior author of the American Association for Cancer Research (AACR) abstract and deputy director of the OSUCCC, said in a statement, “Different types of breast cancer could be affected differently by obesity, a more robust understanding of how obesity triggers inflammatory cancer pathways and increases breast cancer risk could help us develop better chemoprevention strategies or early prevention strategies in women at increased risk based on their weight.”

Young Americans at greater risk

Another finding of the CDC study is that weight-related cancers have increased among younger Americans.

From 2005 to 2014, there was a 1.4 percent increase in cancers related to being overweight and obese among people ages 20 to 49, compared with a 0.4 percent increase in these cancers among people age 50 to 64 set, according to the CDC.

And the obesity rate among American children have gone up in that same time span from 13.9 percent in 2000 to 18 percent in 2016.

The report also found that people who are overweight or obese are also about 30 percent more likely to develop colorectal cancer than individuals with normal weight, according to the report.

And women who are overweight or obese are about two to four times more likely to develop endometrial cancer, the scientists said.

The CDC researchers noted the importance of public health efforts to promote healthy weight.

“The burden of overweight- and obesity-related cancers might be reduced through efforts to prevent and control” excess weight gain and obesity, the studies’ authors wrote.

“Comprehensive cancer-control strategies, including use of evidence-based interventions to promote healthy weight, could help decrease the incidence of these cancers in the United States.”

Food is medicine

Perhaps the takeaway of all this for those with cancer should be the fact that while obesity is a disease and a serious health problem in America, what we eat has an even greater impact on causing and preventing cancer than we previously thought.

There are efforts by a large number of organizations and a growing number of physicians and cancer centers to address this problem and help people enjoy longer, healthier, cancer-free lives.

The announcement last week that an ambitious nine-year study shows a correlation between sugar and cancer could have a positive influence on new cancer-prevention diets and even new treatments for those with cancer.

While the researchers in Belgium admit they don’t fully understand why the cells react this way to sugar, they believe this research in yeast and human cells “has led to a new very valuable scientific hypothesis. The next step is to find out whether these results also apply to patients.”

Meanwhile, Apovian of the Obesity Society is embracing the study as something that could potentially improve and even save lives.

“This is a very significant finding,” she said. “This study corroborates the idea we’ve been studying, which is the overfeeding of sugar and fat in our diet, and how this excess sugar can be utilized by small pockets of cancer cells to grow disproportionately. In other words, the study that excess sugar in our diet is fanning the fire of cancer.”