Excess body weight was responsible for roughly 4 percent of cancers worldwide in 2012, and that number is likely to rise, an American Cancer Society peer-reviewed study has found. The report says that calorific, nutrient-poor food and physically inactive lifestyles are driving up the percentage of overweight people worldwide and promoting noncommunicable diseases, including cancer. By contrast, smoking and infection-related cancers, on the other hand, have reached a plateau or decreased in prevalence.

Published in CA: A Cancer Journal for Clinicians, the review notes that unhealthy lifestyles are promoted by economic systems and marketing practices. Presenting evidence that cancer risk is linked to excess body weight based on regional patterns, the review suggests that policy actions could help tackle the issue. 

“Our current work is examining temporal trends in incidence rates for those cancers we have strong evidence for the excess body weight association. We hypothesized that these cancers may have significantly increased given the increasing trend of excess body weight,” lead author of the study, Dr. Hyuna Sung, tells.

“Indeed, we are seeing some obesity-related cancer rates have increased in contrast to decreasing or reaching a plateau in predominantly infection or smoking-related cancers,” adds Sung.

The report is co-authored by researchers from the American Cancer Society, Imperial College London and the Harvard T.H. Chan School of Public Health.

“Our report shows the proportion and number of cancer cases attributable to excess body weight. By applying the same method, we can also estimate the attributable fraction for other specific risk factors (for example, smoking, alcohol consumption, lack of physical activity and poor diet, etc.) and for multiple factors together,” Dr. Sung says.

“These parameters can quantify how much of cancer burden is attributable to those modifiable risk factors. In other words, it can also tell us how much of the current cancer burden would not be present if everyone didn’t have those risk factors,” she says. 

Further proving the decline of healthy lifestyles, a recent survey by The Health Survey for England (HSE) has revealed that the majority of adults in England are putting their lives at risk through a combination of health risk factors such as being overweight or obese, alcohol consumption, not enough physical activity, smoking and a lack of fresh fruit and vegetables.

Overweight in numbers 
According to the report though, excess body weight has been steadily rising in numbers since the 1970s, and by 2016, nearly 40 percent of adults and 18 percent of children (5 to 19 years old) had excess body weight. This translates to almost two billion adults and 340 million children globally. The steepest increases are found in low and middle-income families, which is a result of lack of physical activity and poor dietary choices.

Four million deaths were linked to excess body weight in 2015 and the worldwide economic impact of illness related to excess body weight is estimated at US$2 trillion.

In 2012, excess body weight accounted for approximately 544,300 cancers, meaning 3.9 percent of all cancers worldwide, with the proportion varying from less than 1 percent in low-income countries to 7 or 8 percent in some high-income Western countries and Middle Eastern and Northern African countries.

Responsible for an array of diseases
Overweight and obesity have been linked to an increased risk of 13 cancers including cancers of the breast, colon and rectum, corpus uteri, esophagus (adenocarcinoma), gallbladder, kidney, liver, ovary, pancreas, stomach and thyroid, as well as meningioma and multiple myeloma. Overweight has been labeled a probable cause of advanced prostate cancer as well as cancers of the mouth, pharynx and larynx.

Adding to the rising number of health threats linked to having excess weight, a study utilizing big data for pediatric research has found one million cases of childhood asthma could be directly attributable to obesity. Led by Nemours Childrens Health System, the research highlights the need to prioritize addressing childhood obesity as it appears to be one of the few preventable risk factors for pediatric asthma.

Income and geography matters
Obesity seems to be higher in wealthy countries wher good economic conditions reinforce habits that promote unhealthy lifestyles. Each US$10,000 increase in average national income is associated with a 0.4 increase in body mass index among adults. 

High-income Asian Pacific countries escape this rule by maintaining traditional dietary habits and active lifestyles promoted by an active transportation system that usually entails a lot of daily walking. Certain low-income Pacific Island nations, on the other hand, show high levels of obesity, ranging from 40 to 65 percent.

“We are also interested in identifying which age groups (young adults vs. elderly) or races or geographic regions are affected most by excess weight, which may help identify target populations for intervention,” says Dr. Sung.

Tackling the issue
The World Health Organization (WHO) has set a target to stop the rise of obesity by 2025, in a move to tackle the rising global burden of noncommunicable diseases, including cancer. The WHO believes that policymakers ought to swiftly act on the issue and governments should implement strategies to combat the promotion of unhealthy foods and change the environment to promote physical activity.

Some of these interventions include: 

Eliminating trans-fats through the development of legislation to ban their use in the food chain. 
Reducing sugar consumption through effective taxation on sugar-sweetened beverages.
Implementing subsidies to increase the intake of fruits and vegetables; limiting portion and package size to reduce energy intake and the risk of excess body weight. 
Ensuring that urban design incorporates the core elements of residential density, connected street networks that include sidewalks, easy access to a diversity of destinations, and access to public transport. 
Providing convenient and safe access to quality public open space and adequate infrastructure to support walking and cycling.
“There is emerging consensus on opportunities for obesity control through the multisectoral coordinated implementation of core policy actions to promote an environment conducive to a healthy diet and active living,” the study authors say. 

The researchers note that the rapid increase in both the prevalence of excess body weight and the associated cancer burden highlights the need for a rejuvenated focus on identifying, implementing, and evaluating interventions to prevent and control excess body weight.

“Finally, we also want to quantify how much of increasing cancer trends can be accounted for by the increase in the prevalence of excess body weight. Because excess body weight alone certainly cannot explain all those trends and other risk factors should play a role,” concludes Dr. Sung.

Just last month in the UK, London’s mayor Sadiq Khan announced a fast food ad ban across the UK capital’s transportation network (Transport for London) in a move to reduce childhood obesity. 

“Reducing exposure to junk food advertising has a role to play in this – not just for children, but parents, families and carers who buy food and prepare meals,” and “tougher action” is required, Khan says.

While on the other side of the pond, the US Department of Agriculture (USDA) has amended the nutrition rules for school meals established under the Administration of former US president Barack Obama, meaning that white bread and low-fat, flavored milk will be back on the menu across US school cafeterias. The move has drawn ire from nutrition advocates and think tanks but has been framed by US Secretary of Agriculture Sonny Perdue as “empowering” and giving “flexibility” back to school cafeterias.