The high cost of healthy food is again being blamed for an alarming rise in obesity levels.

Research just out of Otago University predicts two million New Zealanders will be clinically obese in 20 years, up from 1.1 million in 2015.

Paediatrician Dr David Newman told Mike Hosking a lot of work is going into schools to educate children about better ways of eating.

However, he says what parents can do is limited by their own education and ability to purchase healthy food.

"And when you look at avocados being sort of nine dollars a pop, you realise that a bottle of one and a half litre Coke is only a couple of bucks."

Newman says all that sugar is not good for us.

LISTEN ABOVE AS DAVID NEWMAN TALKS TO MIKE HOSKING