Obese people are contributing to the world food crisis and climate change, experts say.The London School of Hygiene and Tropical Medicine calculated the obese consume 18% more calories than average.They are also responsible for using more fuel, which has an environmental impact and drives up food prices as transport and agriculture both use oil.The result is that the poor struggle to afford food and greenhouse gas emissions rise, the Lancet reported.It comes as the World Health Organization predicts the obese population will double by 2015 to 700m.In the UK, nearly a quarter of adults are classed obese, twice as many as there were in the 1980s.The team found that obese people require 1,680 daily calories to sustain normal energy and another 1,280 to maintain daily activities - a fifth more than normal.The higher consumption of food has a two-fold effect, researchers said.First of all the increasing demand for food, drives up production.This means that agricultural processes are using more oil to meet demand, which contributes to the rising cost of fuel.The cost of fuel is then passed on in the cost of food, making it more difficult for poorer areas to afford it.PricesWhat is more, the researchers said obese people are likely to rely on transport more and put more strain on that transport because of their mass, which again drives up prices and usage.But the researchers said there was a solution.Phil Edwards, who co-authored the article, said: "Urban transport policies that promote walking and cycling would reduce food prices by reducing the global demand for oil and promotion of a normal weight.And they added: "Decreased car use would reduce greenhouse gas emissions."Transport and food policy and the importance of sustainable transport must not be overlooked."But Dr David Haslam, of the National Obesity Forum, said it was "stretching it a bit" to blame the obese in the way that the study appeared to do."Really, it is discriminatory towards obese people. They are an easy target at the moment, but I think the causes of climate change and rising food prices is much more complex."Source: BBC