Barack Obama has conceded that he has lost a bit of weight and got somewhat greyer during his first year as US president, but said he remains healthy despite the relentless demands of his job.

"This has been an extraordinary year, less for me than for the American people: two wars, worst financial crisis since the Great Depression," Mr Obama told NBC television.

"I would be lying if I said that, you know, those aren’t some weighty questions that I carry around on my shoulders every day," he said.

The tall US leader said that his recent apparent weight loss is in line with what has always been.

"My weight fluctuates by 30 pounds – it has for years," he said in a one of several interviews given shortly before departing for Seoul, the last leg of his weeklong Asia trip.

"I’m still wearing some of the same stuff I did when I got married 17 years ago," he said.

"My hair’s gotten a lot greyer, there’s no doubt about that, but I’m not sure that’s (not) just because I was about the age where my hair was going to start getting grey."

Despite the challenges of this first year in the White House, "I think we’ve dealt with them well, and I’m confident that a lot of the work that we’ve done is going to be paying off," Mr Obama said.