In the 1970s the UK population was far slimmer than it is now
Getting back to the relatively slim, trim days of the 1970s would help to tackle climate change, researchers say.
The rising numbers of people who are overweight and obese in the UK means the nation uses 19% more food than 40 years ago, a study suggests.
That could equate to an extra 60 mega-tonnes of greenhouse gas emissions a year, the team calculated.
Transport costs of a fatter population were also included in the International Journal of Epidemiology study.
Dr Phil Edwards, study leader and researcher at the London School of Hygiene and Tropical Medicine, said they had set out to calculate what the UK energy consumption would be if the weight of the population was put back a few decades.
A "normal" adult population, where only 3.5% are classed as obese, was compared with a population where 40% are obese.
These populations reflect the proportions of overweight and obese people living in the UK in the 1970s - and what is predicted for the UK in 2010, the researchers said.
In addition to calculating the increased food costs of the heavier population, the team worked out how much additional fuel would be needed for transportation of modern-day UK compared with the 1970s version.
Greenhouse gas emissions from food production and car travel in the fatter population would be between 0.4 to 1 giga-tonnes higher per 1bn people, they estimated.
And people are generally bigger than they were three decades ago.
Between 1994 and 2004, the average male body mass index (BMI) in England increased from 26 to 27.3, with the average female BMI rising from 25.8 to 26.9 which equates to about 3 kg - or half a stone - heavier.
"This is not really just about obese people, the distribution of the whole population is what's important," said Dr Edwards.
"Everybody is getting a bit fatter."
"Staying slim is good for health and for the environment.
"We need to be doing a lot more to reverse the global trend towards fatness, and recognise it as a key factor in the battle to reduce emissions and slow climate change."
It is not just a UK issue - in nearly every country in the world, the average BMI is rising.
Professor Alan Maryon-Davis, president of the Faculty of Public Health said shifting the population weight distribution back to that of the 1970s would do quite a lot to help the planet.
"In the 1970s we had bigger portions of vegetables and smaller portions of meat and there's been a shift in the amount of exercise we do.
"All these things are combining to hurt the planet and this is a calculation that deserves a bit more attention," he said.