A study by academics from the University of California and Northwestern University claimed that "the causal link between the consumption of restaurant foods and obesity is minimal at best."

It argued that a tax on high-calorie food, as proposed by many health campaigners in the US and Britain, may therefore not be an effective way for governments to tackle the problem.

The study analyzed data compiled by the US Department of Agriculture on calorie intake around the country. It found that people living closer to restaurants were not significantly more likely to be obese than people living further away, indicating that easy access to restaurants had little effect.

Obese people who ate at restaurants, the study indicated, "also eat more when they eat at home."

The US government estimates that about one in three Americans, or 100 million in total, are obese. Last month it was predicted that 75 percent of Americans would be overweight in 2020.

It also showed that while restaurant meals typically held more calories than home-produced food, many customers often offset this by eating less throughout the rest of the day.

The problem is thought to cost Americans between $150 billion and $170 billion in annual medical costs.

The study's authors, Michael Anderson and David Matsa, wrote: "While taxing restaurant meals might cause obese consumers to change where they eat, our results suggest that a tax would be unlikely to affect their underlying tendency to overeat."