PORTRUSH, Northern Ireland - What will Phil do next?

In all the years that question has been asked, not a single person ever thought the answer would be fasting. But that's what Phil Mickelson has gone and done.

The man with the huge game and huge appetite for life and the dinner table looked into the mirror - and charts of his recent play - and determined he needed to make changes. Thus, ahead of the 148th edition of the British Open, to be played over the massive links named Royal Portrush, Mickelson is 15 to 18 pounds lighter than he was 15 days ago.

In a video posted Sunday on social media, Mickelson looked remarkably thinner as he explained he had made a "hard reset to change and try and make things better." The approach included a six-day fast, a brief retreat and consumption of nothing but water and a special coffee blend for wellness.

On Monday at Royal Portrush, where Mickelson had a long session on the practice ground and then joined up with Alex Noren and Matthew Baldwin on the 13th tee and played in, proved the video was not photoshopped. He looked even thinner to me than he did in the video, yet, on those last six holes, he was still hitting bombs and had plenty of bop in his irons and step.

"I didn't fast to lose weight. I fasted to heal," Mickelson told me.

BRITISH OPEN: Rounds 1 & 2 tee times | TV info

MOLINARI:British Open champ has one regret about tattoo he got at 18

The five-time major champion, who won the British Open at Muirfield in 2013 and is a member of the World Golf Hall of Fame, won his 44th PGA Tour title at the AT&T Pebble Beach Pro-Am. Since then, however, he has missed the cut in four of his last six starts and posted just one top-20 finish, a tie for 18th at the Masters.

So the man who has never feared change or the risky shot, who at 49 is still looking for that fountain of golf youth, took food out of his game plan.

"Mechanically, my swing is right where I want it to be," said Mickelson, who also added yoga to his daily routine and set off on many hikes to feed his desire to improve physically and mentally. "But mentally, I've just been losing focus. And my energy wasn't there. So, I needed to make changes.

"The first day, day and a half, was tough. But by the fifth, sixth day, I wasn't craving for food. I feel a ton better. I have so much energy, mental clarity."

Mickelson didn't go willy-nilly into this hard reset. He consumed many reports on studies on improving one's mental and physical being. He talked to doctors about his new pursuit. And a quote he recently came across resonated with him and pushed him to change.

"Everything you put into your body is either causing disease or helping you fight disease."

The quote is the 15th club in his bag as it echoes in his mind and provides incentive moving forward.

"Extensive research shows that fasting lets your body heal itself," Mickelson said.

After he ended his fast, Mickelson became a rabbit. Since returning food to his world late last week, he has followed a plant-based diet consisting of fruits, vegetables, nuts and seeds. As he said, he hardly eats because his smaller stomach quickly fills with one serving.

"And I'm going to stay after it," he said. "I had to make changes. I'm not sure it will help my game. I don't have high expectations this week. But I love this tournament and I'm just going to have fun.

"Hopefully, my game will slowly come around."