Do Obese People Aggravate Global Warming?

May 16, 2008— -- Obesity experts overwhelmingly condemned a letter in the medical journal the Lancet Thursday that suggested growing rates of obesity pose a threat to the environment.

The letter, submitted by researchers from the United Kingdom, implicates the rising tide of obesity in greater oil consumption, more food production -- and, ultimately, in an increase in the release of carbon dioxide and other greenhouse gases.

"It is a significant contribution," said Phil Edwards, co-author of the letter and senior statistician at the London School of Hygiene and Tropical Medicine in the United Kingdom.

"Eighteen percent more food energy is required in many populations where there is a large prevalence of obesity," he said, citing a 460-calorie increase in daily food intake for an obese individual. "There is a clear impact in terms of greenhouse gas emissions in order to grow that food."

Edwards and colleague Ian Roberts wrote in the letter that "more transportation fuel energy will be used to transport the increased mass of the obese population, which will increase even further if, as is likely, the overweight people in response to their increased body mass choose to walk less and drive more."

While some nutrition and obesity experts said the rationale for the findings were sound, they said the research on which the letter is based overlooks more important, well-known factors involved in increased food production.

"We throw away far more food that the extra 460 calories per day they point out," said Dr. Tim Church, chairman in health wisdom at Louisiana State University in Baton Rouge. "In other words, most of our food overproduction is due to waste, not overeating. It is estimated that one-fourth of the food produced in the U.S. goes to waste."

Church added, "Does having 50 extra pounds in a Chevy Tahoe really affect gas mileage? I do not think so."

But more troubling, some said, was the stigma that could arise from the suggestion that those who are obese pose a greater environmental burden than their slimmer counterparts.

"There is enough stigma attached to obesity as it is," said Dr. David Katz, director of the Yale Prevention Research Center in New Haven, Conn. "We should very carefully avoid making it seem as if overweight people are responsible for environmental decline."

"Obese people have enough issues to deal with without being demonized for their impact on the environment," agreed Keith-Thomas Ayoob, pediatric nutritionist and associate professor at Albert Einstein College of Medicine in New York. "The truth is, all people are an environmental burden.

"It is offensive, and I'm not overweight," he said. "I hope the writers are not in the position of seeing patients. They must have missed the lecture on bedside manner."

A Growing Environmental Impact?

Edwards maintains the rationale for his calculations is solid. Out of the roughly 6 billion people alive today, about one billion live in developed countries like the United States and the United Kingdom. It is in such countries that obesity rates are the highest. Edwards and his colleagues created a hypothetical model of these 1 billion people using the U.K. population as a template.

The researchers then divided the total amount of greenhouse gases generated by the world's population -- about 42 billion tons -- equally among the world's population. By this method, each billion-person segment would be responsible for about 7 billion tons of greenhouse gases every year. Edwards estimated that one-fifth of these greenhouse gases are generated through food production -- in total, about 1.4 billion tons.

But assuming that roughly 40 percent of this population is overweight or obese -- the current figures in the United Kingdom -- the 18 percent increase in food demand means that the total amount of greenhouse gases emitted through food production climbs to 1.66 billion tons.

According to these figures, an additional 250 million tons of greenhouse gases may be released every year to sustain an ever more obese population.

"As the population is becoming heavier, more food energy is required in order to maintain that mass," Edwards said. "This is not pointing the finger at people with a BMI [body mass index] over 30. ... I think that the population has the responsibility to be aware that we are seriously impacting greenhouse gas emission by our weight. These are basic physics equations."

But some nutrition experts noted that the equations do not take into account other factors -- many of which could affect the big picture of how our diets affect the environment.

"It is true that obese people eat more than lower-weight people," said Madelyn H. Fernstrom, associate professor and director of the UPMC Weight Management Center in Pittsburgh. "However, it's only in places where there's a lot of food. I don't see this as an environmental issue. ... I understand the concept but do not agree with the authors' conclusions."

Jackie Newgent, a New York City culinary nutritionist and author of an upcoming cookbook on "green" culinary options, agreed.

"The bathroom scale is not a good judge of someone's carbon footprint," she said. "It is possible that if an active, underweight person eats overly packaged, heavily processed, meat-based food that's transported from all over the world, it'll be more problematic for our environment than if a sedentary, overweight person eats too many calories from organic, local, seasonal, plant-based foods."

The Stigma Factor

And then there is the issue of stigma. Increasingly, advocacy groups for people who are overweight and obese have suggested that as obesity rates surge, so too do negative messages and discriminatory policies against these individuals.

"If anyone is taking offense, there is certainly no offense intended," Edwards said, adding that the burden of finding a solution to this problem rests mainly with cities and other urban centers.

"Urban centers are where it is possible to increase active transportation -- transportation policies that encourage people to walk or cycle more."

But even those experts who agreed with the numbers said they fear such a letter, published in a prominent journal, could have a stigmatizing effect.

"I can see the point, that obese people are more likely to use natural resources for transportation and food consumption," said Dr. Sarah Armstrong, director of the Healthy Lifestyles Program at the Duke Global Health Institute in Durham, N.C. "However, my hope would be that this data would not be used to further stigmatize and blame obese people for both their own problems and, now, the problems of the planet."

"Obese people don't need to be told that they may contribute a disproportionate share to the global warming problem," said Dr. Paul Shekelle, director of the Southern California Evidence-Based Practice Center for the RAND Corporation. "Even if it is true, which it probably is, I doubt this would have any beneficial effect.

"Certainly at an individual level, it stretches the imagination to think that this knowledge would be the tipping point for an obese person to finally make the commitment to lose weight."