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Musings of an Energy Nerd

The Connection Between Obesity and Climate Change

Overweight people are disproportionate contributors to global climate change

Our sedentary habits and our diet aren't just hurting our health — they are also contributing to global climate change.
Image Credit: Dospaz

Positive feedback loops that reinforce global warming are scary. Here’s an example of such a feedback loop: warmer temperatures melt Arctic sea ice earlier in the spring and reduce the size of the summer ice pack. Since the dark ocean has less reflectance than ice, a smaller ice pack means that more solar radiation is absorbed by the ocean every summer, further warming the planet.

Another worrisome positive feedback loop arises when warming temperatures melt long-frozen permafrost. The melting permafrost releases methane gas bubbles that have been captive for thousands of years. The release of methane, a powerful greenhouse gas, warms the planet further.

Now researchers are focusing on another feedback loop affecting the global climate: obesity. Here’s how the loop works: when people walk less and drive more, they gain weight. Once they’ve gained weight, they are even less inclined to walk. (Heavier people are more likely to drive and less likely to walk than people who aren’t overweight.) Once this positive feedback loop starts, the number of miles driven continues to increase — and so does the amount of carbon dioxide released into the atmosphere.

The issue is discussed in a paper by Phil Edwards and Ian Roberts, two researchers from the Department of Epidemiology and Population Health at the London School of Hygiene and Tropical Medicine. Their paper, “Population Adiposity and Climate Change”, was published in The International Journal of Epidemiology. “When it comes to food consumption, moving about in a heavy body is like driving around in a gas guzzler,” Edwards and Roberts wrote. “The heavier our bodies become the harder and more unpleasant it is to move about in them and the more dependent we become on our cars.”

Why obesity contributes to global climate change

It turns out that the driving-versus-walking feedback loop is only one of many ways by which obesity worsens global climate change. Among the other factors:

  • In hot climates, overweight people require more energy to cool.
  • Overweight people require more food every day, and the extra food requires fossil-fuel energy for its production, packaging, transport, and refrigeration. Among the reasons that overweight people require extra calories: it takes more caloric energy to move the extra weight. A paper quantifying our population’s excess weight and its climate-change effects (“The Weight of Nations: An Estimation of Adult Human Biomass”) was recently published in BMC Public Health. The study’s lead author, Dr. Sarah Walpole, was quoted in a Climatewire article: “Energy use is a function of the basal metabolic rate. A heavier body needs more food to be sustained.”
  • Overweight people require more fossil-fuel energy per mile to transport, whether by car, bus, train, or plane. In an article called “Worried About Climate Change? Fix Obesity,” Bryan Young quotes Dr. Sheldon Jacobsen, a professor at the University of Illinois, who said, “For every pound the average American is overweight, we use an additional 938 million gallons of gasoline per year. That’s enough to fill 2 million cars with gasoline every year.” Young noted, “It’s a simple matter of physics: the heavier you are, the more energy it takes to move you in your vehicle.”

12 Americans weigh as much as 17 Asians

The average Asian weighs 112 pounds. On the other end of the spectrum, the average North American weighs 178 pounds. Although North America has only 6% of the world’s population, this continent has 34% of the world’s “obesity-related human biomass.” By contrast, Asia has 60% of the world’s population but only 13% of the world’s “obesity-related human biomass.”

Dr. Walpole and her co-authors (David Prieto-Merino, Phil Edwards, John Cleland, Gretchen Stevens and Ian Roberts) used data from the World Health Organization and the United Nations to compare the average body mass index (BMI) in various countries. They wrote, “In 2005, global adult human biomass was approximately 287 million [metric] tonnes, of which 15 million tonnes were due to overweight (BMI > 25), a mass equivalent to that of 242 million people of average body mass (5% of global human biomass). Biomass due to obesity was 3.5 million tonnes, the mass equivalent of 56 million people of average body mass (1.2% of human biomass).”

Summing up, they wrote, “One tonne of human biomass corresponds to approximately 12 adults in North America and 17 adults in Asia.”

Large people have a big carbon footprint

In a Climatewire article discussing Dr. Walpole’s paper, Umair Irfan writes, “If the rest of the world ate, worked and lived like Americans, humanity’s spare tire would swell by the equivalent mass of 935 million average-sized people and soak up the food, water, and electricity of an additional 473 million adults, according to the report. This would mean the average adult would eat an additional 261 calories per day.”

Irfan also imagined a better future: “If Japan were the model for the entire world, global human biomass would shrink by 14.6 million metric tons, equal to 235 million people of average mass. Energy requirements would decrease as if there were 107 million fewer adults on the planet.”

Irfan quoted Ian Roberts, one of Dr. Walpole’s co-authors. “We don’t feed mouths, we feed bodies. We feed flesh,” said Roberts. According to Roberts, “the blame for resource scarcity and ecological degradation should be placed less on poor people having more children and more on the relatively wealthy living unhealthy and unsustainable lives.”

Wealthy and unhealthy

In their The International Journal of Epidemiology paper, Edwards and Roberts calculated that an overweight population requires 19% more food energy than a population with a healthy BMI. They also calculated that lean population of 1 billion people would emit 1,000 million metric tons less carbon dioxide per year than a fat population of the same size.

Global climate change is an unfortunate side-effect of affluence. Compared to the average human, North Americans are wealthier and live in larger houses; we’re also fatter. The trends that have brought us to this point in history are clearly unsustainable. After all, if our houses, chairs, and sofas continue to get bigger every year — presumably, the better to accommodate our increasing biomass — the end of our species isn’t far off.

Last week’s blog: “New Green Building Products.”

Click here to follow Martin Holladay on Twitter.


  1. JoeW N GA Zone 3A | | #1

    About time they noticed
    Thanks, Martin, for this summary -- it's a link that's been waiting to be documented.

    I haven't read the links yet but it needs to be pointed out that this isn't as simple as it seems in some ways. Just two that I can think of --

    Chinese men average (depending on urban/rural environment) 5'5" to 5'7". But US men average 5'10" to 5'11" (the number includes Mexican males who average 5-7). Of course, height doesn't account for the huge disparity of the contrast, but it's clearly a measurement that is a statistical factor. (from Wiki. Yes, I know.)

    It's also interesting to note that obese people die earlier. Chronic obesity reportedly reduces life span by 6-7 years; severe obesity reduces life span by 10 years. Clearly, the total resources used by any human depend on life span.

    I'm sure there are other significant issues, too. It would need to be a book length study. I wish it was instead of a good, if late, beginning.

  2. user-757117 | | #2

    Oh what a tangled web we weave...
    When growth is that in which we believe.

  3. Skip Harris | | #3

    U! S! A! We're number 1!
    Alas. And the lack of numeracy and education in science, logic, and history makes me worry. People seem to prefer soundbites and echo chambers to the hard-edged choices of reality. I worry that humanity will receive the fate it deserves. there any simple and happy solution?

  4. Doug McEvers | | #4

    Take a look in the average grocery shopping cart these days, where's the food? 40 or 50 years ago very few processed snacks were available. Look in the breakfast cereal aisle for instance, what percentage of the space is devoted to minimally processed foods (oatmeal, oat bran, etc.) and how much is something else?

  5. Aj Builder, Upstate NY Zone 6a | | #5

    Martin, it's good your blog is called "Musings"
    We all individually die as of now anyway. Does it matter if we die of what or if we all die at once or if we die fat or thin? It certainly matters if we start not to die. That day is coming. Then things will get real interesting.

    Get out there and enjoy. Whatever living is, it is amazing, fat, thin or other.

    Another offhanded thought. Remember butter bad, now butter good... well... coffee bad, coffee good, alcohol bad, good... exercise good, bad, fat bad... err...well they just said yonder day fat good. Oh and about those long living thin China... folks... not so anymore... fatter... more diabetes... catching up with the rest of us they are... Martin, after your vacation... get your research up to date... by the time you do, this whole article may have to say....hey... be fat...and be happy.

    I say... give me butta! eggs sopping in it with two slices of bacon please and a big mug of coffee

    disclaimer: am a thin GBAer

  6. User avater GBA Editor
    Martin Holladay | | #6

    Response to Joe W
    You're right that Chinese people are, on average, shorter than Americans. But Americans aren't the tallest people in the world; the Dutch are.

    The connections between height, affluence, obesity, and genetics are complicated. Since WW2, the Japanese have gotten taller. So have the Dutch. But Americans aren't getting any taller. For a fuller discussion of these issues, see a fascinating article published in the New Yorker, "The Height Gap."

  7. User avater GBA Editor
    Martin Holladay | | #7

    Response to Ron Keagle
    You're right that there is no direct correlation between income and obesity. However, the countries with high rates of obesity tend to be the wealthier countries, while the obesity rates in the poorest countries of the world are much lower than in the U.S.

    In India and sub-Saharan Africa, malnutrition stunts the growth of a significant percentage of the population. Children and adults in poor countries tend to be much smaller than Americans. To the extent that the world's poor are small because they are malnourished, the small size of poor people in these countries is clearly undesirable. Physicians have identified optimum BMI numbers for health, and it's obviously desirable to have a healthy BMI -- one that is neither too low nor too high.

    In the 1930s, poor Americans were often skinny or small. This is no longer the case; in fact, on average, poor Americans have higher rates of obesity than rich Americans. Sociologists and nutritionists suggest a number of factors that contribute to this phenomenon, including the scarcity of full-service supermarkets in poor neighborhoods; the concentration of fast-food outlets in poor neighborhoods; the fact that high-fat, high-sucrose foods are often less expensive per calorie than healthier options like fresh fruit and vegetables; and the fact that low-income Americans are less educated than upper-income Americans.

  8. Dan Kolbert | | #8

    Reminds me of Vonnegut's Slapstick

  9. User avater GBA Editor
    Martin Holladay | | #9

    Vonnegut's Slapstick
    It's been years since I read Vonnegut's Slapstick, so I had to visit Wikipedia to jog my memory. Wikipedia's Slapstick article includes these sentences in the plot summary: "Western civilization is nearing collapse as oil runs out, and the Chinese are making vast leaps forward by miniaturizing themselves and training groups of hundreds to think as one. Eventually, the miniaturization proceeds to the point that they become so small that they cause a plague among those who accidentally inhale them, ultimately destroying Western civilization beyond repair."

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