High rates of obesity in richer countries cause up to 1bn extra tonnes of greenhouse gas emissions every year, compared with countries with leaner populations, according to a study that assesses the additional food and fuel requirements of the overweight. The finding is particularly worrying, scientists say, because obesity is on the rise in many rich nations.

"Population fatness has an environmental impact," said Phil Edwards, from the London School of Hygiene and Tropical Medicine. "We're all being told to stay fit and keep our weight down because it's good for our health. The important thing is that staying slim is good for your health and for the health of the planet."

The study, carried out by Edwards and Ian Roberts, is published today in the International Journal of Epidemiology.

In their model, the researchers compared a population of 1 billion lean people, with weight distributions equivalent to a country such as Vietnam, with 1 billion people from richer countries, such as the US, where about 40% of the population is classified obese.

The fatter population needed 19% more food energy for its energy requirements, they found. They also factored in greater car use by the overweight. "The heavier our bodies become the harder it is to move about in them and the more dependent we become on cars," they wrote.

The greenhouse gas emissions from food production and car travel for the fatter billion people were estimated at between 0.4bn and 1bn extra tonnes a year. That is a significant amount in comparison with the world's total emissions of 27bn tonnes in 2004.

Last September the world's leading authority on climate change suggested the people should eat less meat, because meat production causes 20% of global emissions. Rajendra Pachauri, chairman of the UN Intergovernmental Panel on Climate Change, said consumers should begin with one meat-free day a week.