Leading academics have clashed over whether there really is an obesity epidemic.

Claims that we are in the grip of an epidemic "often exceed the scientific evidence and mistakenly suggest an unjustified degree of certainty", said Patrick Basham, professor at John Hopkins University in Washington DC, and John Luik, senior fellow at the Democracy Institute in London, in this month's British Medical Journal.

"Much of the data on overweight and obesity are limited, equivocal and compromised in terms of extent and the reliability of the measurements and the populations sampled," they claimed. "In the US, for example, data about population weights date from only 1960." This made it impossible to establish what constituted "normal" levels of obesity, they said.

But Professor Robert Jeffery of the University of Minnesota and Nancy Sherwood, research investigator at HealthPartners Research Foundation in Minneapolis, also writing in the BMJ, said there was "an abundance of observational and experimental data" that showed obesity was becoming more prevalent.

"The fact that obesity is developing rapidly in many parts of the globe is incontrovertible," they claimed, quoting WHO figures indicating obesity rates nearly quadrupled in Britain from 6.2% of the population in 1982 to 22.6% in 1999.

Obesity rates in Japan and the US tripled over a similar period, they added.

The academics were writing in response to a claim by UK health secretary Alan Johnson last month that Britain was in the midst of an obesity epidemic.