He rules Hell's Kitchen, but in hell's oven Gordon Ramsay is just another suffering Ironman triathlete.

The 46-year-old celebrity chef will be among 2000 competitors on Sunday (AEDT) in the Hawaiian Ironman world championships.

It is triathlon's most famous race and is notorious for its brutally-hot conditions.

Ironman consists of a 3.8km swim, 180km cycle and 42.2km marathon run.

The Queen K highway, where much of this race is held, cuts through black, barren lava fields that radiate heat.

The exposed terrain also leaves the triathletes at the mercy of severe trade winds off the Pacific Ocean.

"You step off that plane (at Kona Airport) and that's when you really do ... start crapping yourself," Ramsay said at Friday's pre-race media conference.

"Just listening to the pro athletes and watching how buoyant and excited and ambitious they are, that's when it hits home.

"I'm honoured to be here.

"The 'hay is in the barn' and I just want to go out there and enjoy it, put my head down and get to that finish line."

Apart from his culinary ability, Ramsay is also well-known for his fiery temper.

It begs the question - what will happen at an aid station mid-race if Ramsay asks for water and he receives a sports drink instead?

But Ramsay played down his reputation, saying it was due to passion.

"You don't win three Michelin stars by being a nice guy in the kitchen," he said.

"It's a very similar parallel, when you look at the disciplines across this training regime.

"I've been as passionate in my training as I have in my career."

Ramsay, never a stranger to controversy, has come in for criticism that he did not qualify for Hawaii.

It is a regular bone of contention in the sport that the Hawaiian Ironman invites big names such as Ramsay for the publicity they bring, rather than making them qualify.

"I've taken a lot of shit this week because I haven't qualified," he said.

"There's no secret behind that, but I've put the training in and I'm blessed to be here."

The keen marathoner has changed his diet, even eating less meat, and has shed plenty of weight to be Ironman-ready.

"I've seen brown rice in so many different ways, you've got no idea," he said.

"I hate to say it, but secretly, (I have been) slightly vegetarian, somewhat vegan.

"It's been an interesting transition."