"That one's been floating around for a few years and only a month or so ago we had another query about it," Allan said.
Another widely-heard myth was that there were antibiotics in chicken meat. But it had been years since any antibiotic residue had been found in chicken meat - "There's quite a stringent testing programme," in New Zealand."
Catherine Sissons, of Nova Nutrition, said most of her new clients arrived with incorrect beliefs about food.
Common ones were that carbohydrates were always bad for weight loss, that people who exercise could eat what they liked, and that calorie counting was the best way to lose weight.
"It's quite worrying how many people are scared of potatoes."
Massey University professor Steve Flint was concerned about the increasing popularity of raw milk among people who believed it was healthier that pasteurised milk.
But the raw product could contain tuberculosis.
"We pasteurise milk to make it safe. If we didn't have to, we wouldn't."
Allan said most of the myths were not dangerous but some could be damaging to diets.
"Lots of people seem to think butter is better than table spread, but from a nutritional perspective, it's high in saturated fat."
The Heart Foundation has a page on its website dedicated to myths about margarine, including that the spread was invented to fatten turkeys but killed them instead.
You want lies with that?
McDonald's created a website answering customer questions about its food - and discovered widespread urban myths about the golden arches. The site, yourquestions.mcdonalds.co.nz, started running in November and has received more than 1000 questions.
Spokeswoman Kim Bartlett said most had been on three themes: Whether there is pig or chicken fat in shakes, what goes into Chicken McNuggets and whether burger patty meat is bleached.
Bartlett said rumours about McDonald's ingredients had become the stuff of folklore.
"We decided it was time to clear a few things up."
For the record: Shakes do not contain animal fat, Chicken McNuggets are made with 100 per cent chicken - breast and some skin - and patties are not bleached or treated with ammonia.