NSW Liberal MP Peter Phelps has compared the State Government's healthy canteen strategy to sex acts, suggesting students are being told that oral sex is "OK" three times a week but sausage rolls can only be had once a semester.

There are now calls for Premier Gladys Berejiklian to pull Dr Phelps into line after he criticised his own Government's new healthy school canteen strategy.

Dr Phelps denied there was a child obesity epidemic while criticising the messages of sex education in state schools.

"Welcome to the New South Wales education system," he said.

"Where students can be told 'it's OK to fellate your boyfriend three times a week, but because of health requirements you can only have a sausage roll once every semester'."

Dr Phelps said "public health totalitarianism" was expanding not only in NSW but across the whole nation and "nanny state-ism" has reached an "insidious" level.

It is not the job of the Government to instruct people how to live nor to tell parents how to raise their children, he said.

Students are given no choice in the new healthy school canteen strategy, the MP said, and the obesity epidemic is a "myth".

"It is all about control," he said.

Peter Phelps says the childhood obesity epidemic is a "myth". ( Facebook: Peter Phelps )

"There is a willing cohort of public health activists who are always ready to fabricate a crisis to get on the public teat and get a bit of Government money."

The Government's Institute of Health and Welfare says one in four Australian children were overweight or obese between 2015-2016.

Discretionary foods — those that are not necessary to provide the nutrients the body needs and are often high in saturated fats, sugars and salt — made up 39 per cent of children's energy intake between 2011-12.

The Opposition's health spokesman, Walt Secord, said Dr Phelp's remarks crossed the line.

"I think it's time the Premier acted on Dr Phelps ... he does this on a weekly bases he just makes outlandish, outrageous comments and he is beginning to treat the Parliament like a 1950s locker room," he said.