Restaurant critic Egon Ronay has called on the government to provide clearer information about organic food.
Organic food sales in the UK are said to have risen by 30% in 2006
Shops and producers were profiting from public confusion about the issues, he told the BBC.
Mr Ronay - among several food experts to have questioned the way organic products are marketed - said there is no scientific proof they are healthier.
The Soil Association maintains that studies have shown that there are more nutrients in organically produced food.
Last month, the Environment Secretary David Miliband sought to clarify his views after telling a newspaper there were no "proven" health benefits and non-organic food should not be seen as "second best".
He said people, including himself, buy organic food for taste and environmental benefits.
Mr Ronay said Mr Miliband's comments had further confused the situation.
He said people are buying organic food in the belief that it is a healthier alternative to conventionally produced food.
"The public has no clear idea what organic food is," he said.
"We're being conned and I think the minister ought to be pinned down and ought to be challenged to spell out in terms that the public can clearly understand what is organic food."
According to the Soil Association, organic food sales in the UK increased by 30% to £1.6bn in 2006.
The organisation said it has written to the environment secretary "outlining evidence coming from his own department" backing claims that organic produce was healthier.
Robin Maynard, director of communications for the Soil Association, said: "I have a great deal of respect for Egon Ronay because he has done an awful lot of good in promoting healthy, unprocessed seasonal food...
"But I think he has got it wrong in his criticism of organic food."
Mr Ronay later pointed out that he had not criticised organic food, only called for clearer information.