Men are vastly better than women at losing weight because they view it as "a war", the international head of Weight Watchers said.
Visiting Australia this week, the organisation's chief executive David Kirchhoff, based in the US, says this fact annoys women, who are also burdened by a barrage of negative body image stereotypes.
Mr Kirchhoff, who lost 20 kilograms using the program he now runs, said men are typically more successful at losing weight because they approach it in a combative frame of mind.
"Here's the dirty little secret when it comes to men and women losing weight: men can lose weight really quickly when they put their minds to it, almost to the point where when men finally decide to deal with a weight loss issue, it's almost like they go to war," he said.
"When men are doing the Weight Watchers program, which is based on keeping track of points, as soon as they start doing it, it becomes like a fantasy sports league.
"They keep track of scores and numbers … they do so unbelievably well … And it irritates women."
The biggest hurdle for men is making the decision to start, Mr Kirchhoff said, often because it is considered less socially acceptable for them than women to admit they're on a diet.