Dr Libby became involved with the brand in 2012 when she was offered the previous-generation CT hybrid to drive from Wellington to Auckland during her speaking tour.
• Read more Car Buyers' Guide: Lexus hatch
She was so impressed with Lexus' hybrid system that she researched the petrol-electric engine's fuel-saving technology.
"I'm all about sustainability and helping people take better care of their bodies, so the message that comes with the hybrid system is doing what we can for the environment," she said.
Lexus NZ was equally impressed with the Australian, who has lived in New Zealand for the past seven years and travels the world giving seminars, including speaking alongside American TV host Dr Oz in front of 9000 people in the US.
Lexus NZ assistant marketing manager Andrew Davis said the company was "thrilled to be partnering with Dr Libby, someone who shares synergies with the Lexus brand and philosophies".
"Dr Libby is renowned for helping Kiwis make meaningful lifestyle changes; ones that have a lasting impact on their health and wellbeing and the environment around them," said Davis. "It's the same positive outlook that resonates strongly with Lexus enthusiasts who choose hybrid technologies."
Dr Libby has written bestselling books such as Accidentally Overweight, Rushing Woman's Syndrome and Real Food Chef and is now in Australia writing her sixth.
But before she left she was given the keys to the latest CT200h.
Libby Weaver, Lexus ambassador, with her Lexus CT200h. Pictures / Ted Baghurst
"It's such fun to drive. I love the environmental sustainability of it, I love that you can go further for less - for me that's a catch-cry I link to the car," she said.
"Around town I drive it in the eco mode - it's fantastic in stop-start traffic. And then in the open road I would put it into sport mode for a couple of patches for that pleasurable drive."
Dr Libby's most memorable road trip was a day trip across the North Island - from New Plymouth to Napier with a lunchtime speech in Taupo.
"It was really amazing for me to drive across the country [compared to trying to drive across Australia]. The scenery was amazing.
• Read more: Dr Libby Weaver's latest winter wellness tip
"It was very special and very fun. I don't just talk to people about nutrition, because I approach things holistically, and one of the things I talk about is things that bring them pleasure and that was certainly a highlight for me.
"I love driving by myself. It's one of my favourite things in the whole world to do - I've got great music and a great car."
Her favourite music to listen to when driving is Massive Attack and John Denver, with some Kylie Minogue thrown in.
Dr Libby grew up in the Australian town of Tamworth and her first car when she was a university student was a late 1980s Corolla "with 135,000km on the clock".
"My dad thought I was crazy buying a second-hand car with so many ks on it, but I drove it until it gave up the ghost with 435,000km on it and only having to replace the brakes. My dad has now owned two Corollas."
Tips to help keep you safe behind the wheel
With school holidays starting this weekend many families will be taking road trips. Before you get behind the wheel, follow Dr Libby's tips for a safe journey.
• The best meal a driver should have before a long road trip is something that sustains you, so foods that contain protein and fat such as eggs.
An ideal breakfast would be a cooked egg meal "because when you eat warm food your digestive system handles that really well".
• Don't forget the kids because a cooked breakfast is sustaining for them, plus the more stable their blood-sugar levels are, the less likely they are to get hungry quickly or to fight. "When blood sugars are low we can get a bit snappy and impatient," says Dr Libby.
• Snacks are important. Rather than having to rely on poor-quality roadside snacks, pack things that people like - but don't pack carrot sticks if people aren't going to eat them. An easy snack is nuts and raisins, or try Dr Libby's "brain balls" from her recipe books: ground-up nuts and seeds plus dates for sweetness and cocoa powder for chocolate flavour.
• Forget drinking strong coffee before a long road trip. Dr Libby suggests drivers should have green tea because it has a small amount of caffeine in it and a substance called theanine - an antioxidant that helps buffer the caffeine and gives you a more gentle, relaxed state instead of being hyped up on coffee.
