New research shows high carbohydrate foods are the main contributor to tooth decay in young people, along with processed sugar.
The research, which was carried out by Auckland Univerity of Technology, found eating a lot of carbs is linked with poor dental health and obesity.
This is at odds with the government-endorsed guidelines, which recommends young people eat high amounts of carbs.
Public health researcher Sarah Hancock told The AM Show on Monday the disconnect is an issue because New Zealand spends a huge amount removing kids' rotten teeth.
"It's $132,000 each working day, that's what every taxpayer wakes up to spend. Thirty children today will wake up and have their teeth removed."
Hancock said that figure only includes pre-schoolers who are five years old and under.
She said the children's parents often don't realise there is anything wrong because the food causing the decay is portrayed as healthy by the government.
Foods like cereals, muesli bars and muffins are particularly bad, according to Hancock.
"At least 70 percent of the foods you find in the supermarket can be classified as ultra-processed foods which contain a lot of high starch, high sugar."
However, she said the guidelines suggest eating those foods as part of a healthy diet while avoiding full-fat dairy products, which actually protect teeth from decay.
"There is no evidence of any harm [from full fat] in fact on the contrary, the evidence is that there is benefit in oral health because cheese and milk protect against tooth decay."
Hancock said eating whole foods and unprocessed meats, eggs and dairy is the best way to go.
She said the perfect school lunch includes salad, chicken and a hard-boiled egg.
The Ministry of Health recommends eating plenty of fruit, vegetables and whole grains. It suggests eating some milk products but making sure they're mostly reduced fats. Also eating some legumes, nuts, seeds, fish and other seafood, eggs, poultry eg, chicken and/or red meat with the fat removed.