Obama had snipers watching him with Bear Grylls

US President Barack Obama with Bear Grylls in a scene from the TV show Running Wild with Bear Grylls.

They shared tea made out of flower clusters, ate wild salmon picked over by a bear, talked about being a dad and discussed climate change - all while snipers kept watch from the mountains and the official food taster looked on warily.

US President Barack Obama's Running Wild Alaska episode with British wilderness expert Bear Grylls airs on Sky's Discovery Channel this week, and Grylls said the short trip shows an intimate and fun side of Obama that has rarely been seen.

"He said it was one of the best days of his presidency," Grylls told reporters.

"There were times along the route I had to pinch myself and think, 'actually, this is the President of America'."

The episode was filmed in September on a trek to Alaska's shrinking Exit Glacier that was aimed at drawing world attention to climate change.

Last year alone, the Exit Glacier melted and retreated 57 metres toward the Harding ice field, which has itself lost 10 per cent of its mass since 1950.

Obama is the first sitting president of any nation to take part in Running Wild with Bear Grylls, following in the footsteps of celebrities like Ben Stiller, Kate Winslet and Zac Efron.

Grylls, a former SAS soldier turned adventurer and survival specialist, said the idea for the TV episode came from the White House.

"They (the White House) approached us, saying would we consider taking the president on an adventure to Alaska. I almost didn't really believe it. I thought this was a spoof," Grylls said.

Grylls said a team of about 50 Secret Service personnel, a food taster, snipers and helicopters accompanied the pair during the day-long trek through a forest and across a glacial outwash.

Obama threw himself into it, shrugging off the food taster, sharing Gryll's water bottle, lighting fires and eating berries.

"He didn't have any problems. He wanted the physicality ... he was up for everything," Grylls said.

Asked what he had learned from the trip, Grylls quipped: "Whoever you are, everyone puts their trousers on one leg at a time."

• Obama's Running Wild with Bear Grylls episode airs Friday, December 18 at 7.30pm on Sky's Discovery Channel.

- AAP