Dr Libby describes how the importance of burning calories was drummed into her early education.
While at university, she would run for two hours almost every day of the week and felt happy, healthy and slim, so believed she had the balance right.
After graduating with a degree in biochemistry, Dr Libby started work at a health retreat and she no longer had time to run.
"I had gone from being Little Miss Runner, burning bucket-loads of calories, to little Miss Tai Chi, hardly burning any at all.
"Despite burning fewer calories, my clothes got looser and looser.
"This completely fried my brain, because based on the way I had been educated, the precise opposite was supposed to happen."
Subsequent research led to the revelations that inspired Accidentally Overweight and the latest book is a further exploration of the calorie equation.
"I read some research that was first published in 1918," says Dr Libby.
"There were no processed packaged foods available, so all the foods in the study were real foods. I don't like to use the word toxins, because people are not ingesting poisons, but the ingredients in packaged foods are very hard for the body to break down.
"If people gradually start replacing meals with real food, it doesn't have to be difficult or expensive. Some of the recipes in my books will feed six people for a cost of around 75 cents per person and there are usually leftovers that can be stored to eat later."
From Tamworth, New South Wales, Dr Libby is married to Aucklander Chris Weaver and they divide their time between Australia and New Zealand.
She is currently on a New Zealand-wide tour and will be appearing next Tuesday at the War Memorial Conference Centre, Watt St, Wanganui, starting at 12.30pm.