Instead, he says it suits society to turn a normal physical characteristic into a disease.
"The claims that we are in the midst of a public health crisis because of increasing body mass are very poorly supported by the actual evidence.
"In fact, we are looking at a classic moral panic.
"A rather small, or in many cases an imaginary health risk, is being blown out of all proportion because of social factors."
Prof Campos, a law professor at the University of Colorado, was in Dunedin this week to speak at the University of Otago "Big Fat Truth" international research symposium, which finished yesterday.
He has spent more than 10 years researching the link between obesity and health risks and published a book on the subject, The Obesity Myth, in 2004.
Three much more fundamental issues influenced society's attitudes towards obesity, he said - a contempt for fat people which was translated into health claims, a desire by pharmaceutical companies and others to justify the sale of diet pills and weight loss programmes, and "upper-class, white, women academics projecting their eating disorder neuroses about food and body image into their data".
Prof Campos said there was "tremendous resistance" to his views.
"It is difficult to get people to even consider that a concept like obesity is poorly defined and badly overblown."
While he supported the view people should exercise more and eat a balanced diet, he said research showed up to 98% of overweight people were unable to keep up that lifestyle and thus did not lose weight.
"The notion that body weight is plastic is crucial to the [view] that fat is unhealthy because if body weight isn't modifiable, then turning a physical characteristic into a disease is a really terrible idea.
"There are all kinds of serious health risks associated with being a man . . . But nobody goes around saying, 'Well, what are we going to do about the masculinity epidemic?' Part of the reason for that is because people do not think gender is a modifiable characteristic."
Prof Campos' interest in obesity came about while preparing a conference almost 12 years ago on the impeachment proceedings against then United States president Bill Clinton.
He studied media coverage of Mr Clinton's sexual relationship with 22-year-old White House intern Monica Lewinsky.
"There were a huge number of stories which focused on her weight, which at the time I thought did not seem to be relevant to anything.
"More than 100 of them used the term zaftig, a [Yiddishism] used to describe a curvaceous woman - a babe.
"What I discovered was that zaftig was really a euphemism for fat."
Prof Campos believed an obsession with fat surrounded the relationship, with the view that "fat was bad".
But he said when he examined the medical data supporting that view, he was "stunned".
"People were making hysterical claims about obesity which, in the main, could not be substantiated."
At first, his views were considered extreme, he said.
But in recent years a variety of social scientists and some medical professionals and academics had begun to express similar views.
"Now, I am seeing actual engagement and argument at the academic level, and I am tremendously encouraged by that."
