肥満が地球温暖化を加速する?

 肥満の増加により、石油消費の増加、食糧増産となり、最終的に二酸化炭素などの温室効果ガス排出の増加となる。
画像 肥満により一人460カロリーの食物摂取の増加となり、多くの国で18%多くの食物エネルギーが必要となると、英国の研究者が試算し、Lancet に発表された。
 実際には460カロリー以上の食物が廃棄され、米国では生産された食物の1/4が無駄になっていると概算されている。食べ過ぎよりも無駄の方が大きいと指摘する研究者もいる。50ポンドの体重増加が本当に石油消費に影響するだろうか? すべての人間が環境の負荷になっている事が事実である。
 約60億の世界人口のうち、約10億人が米英などの先進国にいる。世界で発生する約420億トンの温室効果ガスのうちの約70億トンがこの10億セグメントが責任があり、1/5の約14億トンが食料生産を通して生成されると概算した。英国のように40%が肥満であると仮定して、食料生産を18%の増加として16億6000万トンまで上昇し、肥満の維持に追加の2億5000万トンの温室効果ガスが排出されると試算している。
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Do Obese People Aggravate Global Warming?
Researchers Say Obesity Epidemic Threatens Environment
By DAN CHILDS
ABC News Medical Unit May 16, 2008
http://abcnews.go.com/Health/Diet/Story?id=4865889&page=1

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.
global warming and weight
U.K. researchers say rising obesity rates may contribute to global warming.
(ABCNews Photo Illustration)
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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."
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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."

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The Lancet 2008; 371:1661
DOI:10.1016/S0140-6736(08)60716-3

Correspondence

Transport policy is food policy

Phil Edwards email address a and Ian Roberts a

We endorse the call for fair and sustainable solutions to tackle the causes of global food insecurity (April 26, p 1389),1 but argue for greater recognition of the importance of reducing the demand for transportation fuel in resolving the struggle for energy between people and cars.


Click to enlarge image

Science Photo Library

Petrol tanks and stomachs were competing well before biofuels were proposed to tackle climate change. Motorised transport is more than 95% oil-dependent and accounts for almost half of world oil use.2 Because oil is a key agricultural input, demand for transportation fuel affects food prices. Increased car use also contributes to rising food prices by promoting obesity which, for the reasons outlined below, increases the global demand for food.

We estimate that a population of 1 billion people with a stable mean body-mass index (BMI) of 24·5 kg/m2 consumes an average 6·5 MJ of food energy per person per day to maintain basal metabolic rate, and a further 4 MJ per person per day for activities of daily living. An obese population of 1 billion people with a stable mean BMI of 29·0 kg/m2 would require an average 7 MJ of food energy per person per day to maintain basal metabolic rate, and 5·4 MJ per person per day for activities of daily living (calculations available from the authors). Compared with the normal weight population, the obese population consumes 18% more food energy. Additionally, 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.3

Urban transport policies that promote walking and cycling would reduce food prices by reducing the global demand for oil, and promotion of a normal distribution of BMI would reduce the global demand for, and thus the price of, food. Decreased car use would reduce greenhouse gas emissions and thus the need for biofuels, and increased physical activity levels, would reduce injury risk and air pollution, improving population health.

Transport policy is food policy and the importance of sustainable transport must not be overlooked.

We declare that we have no conflict of interest.

References
1. The Lancet. Finding long-term solutions to the world food crisis. Lancet 2008; 371: 1389.
2. Woodcock J, Banister D, Edwards P, Prentice A, Roberts I. Energy and transport. Lancet 2007; 370: 1078-1088.
3. Swinburn B, Egger G. The runaway weight gain train: too many accelerators not enough brakes. BMJ 2004; 329: 736-739.

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