Being overweight or obese is the culprit of four percent of cancers worldwide, a new study estimates.
Already, two thirds of Americans and more than two billion people worldwide are overweight or obese, and experts only expect those numbers to rise in the coming decades.
Poor diets abound, in the Western world especially, and ascribing to them contributes to risks not only for obesity itself but for seven of the 10 leading causes of death in the US.
Now, a global study conducted by Harvard University and Imperial College London suggests that excess body weight isn’t just a risk factor, but responsible for 544,300 cancers a year worldwide.
But the rates vary significantly. Obesity accounts for nearly seven percent of cancers in the US where citizens are wealthy but inactive - and less than one percent in poorer nations like Ethiopia and India.
The authors urge public policy chances to reverse the upward trend of both obesity and its associated cancers.
Obesity has reached epidemic proportions in the US and other Western countries.
Identifying a clear start for the epidemic is nearly impossible, but waistlines and BMIs have been growing in the US since the 1970s, when no more than seven percent of the American population was obese and 13 percent was overweight.
By 1990, obesity rates had more than doubled in the US, to 15 percent of the adult population.
In the 20 years since, the problem has quickly escalated. Now, one in three American adults is obese.
It’s pretty clear why being overweight or obese is harmful to the heart and increases risks for diseases like diabetes.
But the direct line between excess body weight and cancer remains unclear. The current dominant theories suggest that overweight people’s higher insulin and insulin growth factor levels may encourage the growth of cancers, or that obesity-related inflammation itself might be carcinogenic.
Overweight women, in particular, may have higher levels of estrogen that contribute to the development of breast and endometrial cancers.
Previous research has found that there are 13 particular cancers that being overweight or obese raise risks of developing, and recent developments point to being overweight as a likely cause of prostate, oral and esophageal cancers.
While it did not aspire to working out the mechanism behind high body weight and cancer, the new research does describe the possibilities and presents a wide range of health and lifestyle data suggesting that obesity is causal to cancer - and why matters may only get worse.
For example, the researchers identified wealth as the most significant driver of obesity - though its effects vary regionally - and, in turn, in obesity-related cancers.
In wealthy Western countries, rates of obesity are particularly high, as is the proportion of cancers related to obesity.
Rates of obesity-linked cancers were highest in Egypt, Mongolia and Puerto Rico.
The US ranked eighth worst, as 6.9 percent of all cancers could be traced to obesity.
On the other hand, Ethiopia, India and most countries in Southeast Asia all had rates of obesity-related cancers of one percent or less.
The distinction between wealthy countries with high rates of these cancers and those with wealth but less cancer came down to societal habits.
Some wealthy nations, such as those in the Asian Pacific, have dodged cancers of obesity because their traditional diets are low-fat and their infrastructures require or encourage people to walk on a daily basis.
The opposite is true in the US, where diets tend to be high in carbs, sugar, fat and red meat, and there is nearly one car for every American.
At the top of its list for public heath priorities, the WHO wants to curb rising rates of obesity worldwide to reduce cancers and the burden of other related diseases, and it sees chancing societal risk factors for obesity as a crucial element to that plan.
‘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,’ the study authors wrote.
‘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.’