Federal Sport Minister Bridget McKenzie has apologised for appearing to mock overweight people at a national obesity summit in Canberra.

The deputy leader of the Nationals apologised after being photographed puffing out her face and rubbing her stomach while standing next to a banner advertising Friday's summit.

Ms McKenzie blamed her actions on a bad reaction to breakfast.

"The issue of obesity is a matter I take very seriously and would never triavisie [sic] it - or to add in any way to stigmatisation," she tweeted.

"I sincerely apologise for this very unfortunate photo taken as I demonstrated how my stomach felt after scrambled eggs reacted w yogurt I had just eaten."

In a statement released on Friday, the senator said two thirds of adults and a quarter of children aged five to 17 years were overweight or obese.

She said groups more likely to be overweight or obese included men, the socioeconomically disadvantaged, people without post-school qualifications, Aboriginal and Torres Strait Islanders and those born overseas.