The London School of Hygiene and Tropical Medicine calculated in a recent study—whose results were published in The Lancet —that obese people consume 18 percent more calories than non-obese people. They got to that number by considering how many calories a population of non-obese people (those with an average BMI of 24.5) would need to consume to keep their weight stable with those a population of obese people (BMIs over 29) would need. Let's leave aside for a second the fallibility of BMI (well-documented by Kate Harding here ) as a measure of health, well-being, or, frankly, fat; let's ignore also the presumption that neither of these hypothetical populations exercise or do anything to increase their caloric needs other than being fat. (Although I don't anticipate I'll see the headline "compulsive exercisers to blame for world's ills" any time soon.) Let's even accept the study's premise that fat people stay fat simply because they eat more.The conclusions still don't follow the data.Here's what the study found: Because of their greater food consumption, obese people drive up global demand for food, raising food prices worldwide. Higher demand for food also increases agriculture's need for oil, driving fuel prices (and thus food prices) higher. Finally, fat people drive more and use more fuel when they drive—all that extra weight!—which contributes to global warming and drives fuel prices higher still.Let's look at these conclusions one by one.Conclusion #1: Fat people are to blame for global warming because they drive everywhere and cost more to move around.First of all, the study cites no data in claiming that overweight people drive more than people of normal weight. Assuming no physical impediments to walking (being wheelchair-bound, for instance), the amount a person drives is determined far more by urban planning—how accessible and user-friendly is the transit system? Is the grocery store/cinema/video store within walking distance? Does the city encourage alternative forms of transportation like biking, or are bike paths spotty and hard to navigate?—than by whether he or she is overweight. You'll see a lot more people of all shapes and sizes walking where I live, Seattle, than in Houston, Texas, the car-dependent city where I grew up. So doesn't it follow that Houston-style planning is the real problem—not whether a person's BMI is a few ticks north of "normal"?As for the "drag" issue: I don't know whether 10 or 40 extra pounds makes much difference in the amount of fuel a person uses, but I do know this: Hauling around a big family—to say nothing of the climate impact of having a big family—has got to add more to fuel costs (both in weight and the cost of fueling a bigger car) than being overweight. The reason you won't see a story titled "Breeding blamed for world's ills" is that being fat is discouraged, and having children isn't.Conclusion #2: Fat people are to blame for high food prices, because increased demand for food drives up production, which drives up fuel prices, increasing the cost of food.No, no, no, no, no. What drives production isn't demand for more food. We have more food than we can consume—some 3,900 calories a day for every man, woman and child in the country, or nearly twice what most people consume. Fat people aren't clamoring for still more, more, more Cherry Cokes, Twinkies, and sugar cereals—the US food system is producing them because they have to find new ways to make us eat as much as possible. Blame the producers, not the consumers.Meanwhile, there are plenty of reasons food costs are rising. Among them: An agricultural system that subsidizes commodity crops like corn, taking food crops out of the food supply (ironically, in response to increased demand for ethanol because of rising fuel prices); demand for US exports in developing countries like China, where meat production is rising' drought and other weather crises, quite possibly the result of climate change; and the globalization of the world's agricultural systems, which forces small countries to import most of the food they once produced locally. And, of course, fuel costs.Conclusion #3: Fuel costs are rising because fat people are increasing the demand for gas.This one's the easiest to debunk. Fuel prices aren't rising because fat people drive more (until very recently , in fact, we were all driving more); fuel prices are rising because we're running out of easily accessible oil. The harder oil is to get, the more it's going to cost. That situation isn't going to reverse itself until we invent new technologies, start investing in alternatives to driving, or both; but blaming high gas prices on fat people is definitely the wrong place to start.Interestingly, the conclusions of the study itself (as opposed to the media's hyperventilating coverage of the study) don't contradict that. In the first paragraph of the Lancet article, the two men who performed the study argue that we need "argue for "greater recognition of the importance of reducing the demand for transportation fuel in resolving the struggle for energy between people and cars." But given the choice between encouraging people to eat less and, I don't know, supporting alternatives to driving, I know which one I would pick. Cross-posted .)