"Three months of eating is kind of rough on the health," said Gault.
"I've just managed to lose a fair amount of weight and didn't want to put it back on."
Gault had appeared on the celebrity chef judging panel alongside the late Ross Burden, Ray McVinnie and Josh Emett since the show debuted in 2010. "It's been five seasons for me and I've absolutely loved every minute of it."
The programme had served to inspire people about food and provided a platform for those who wanted to pursue a career in the industry, Gault said.
Past winners have gone on to become household names following the release of cookbooks and appearances in advertising campaigns and other television shows.
They include second-season winner and recently appointed Avocado Ambassador Nadia Lim, who used her profile to launch a home delivery food business and is now appearing as a guest judge on reality cooking show My Kitchen Rules.
First-series winner Brett McGregor and finalist Jax Hamilton have become television regulars fronting supermarket meal plans.
The show's most recent winners, Maketu sisters Karena and Kasey Bird, have a popular food column in the Herald On Sunday.
A TVNZ spokesman said MasterChef NZ had a great five-year run but the network had made the decision not to press ahead with a sixth season.