IT is famously known as Scotland's other national drink and is apparently made of girders.

For Leigh Griffiths, however, if he had kept on downing the stuff like he once did then Celtic manager Ronny Deila may well have questioned the player's mettle and put him on the 'bru'.

The Celtic and once more Scotland striker's latest life lesson has been to cut out the fizzy drinks in a bid to reduce his body fat and prove to Deila that he has taken in everything the Norwegian has lectured.

If you are not super fit at Celtic then you don't play.

If you can't get a game for your club then Scotland manager Gordon Strachan won't be interested.

Griffiths saw the way things were going and decided to make a couple of changes.

He went from being a fringe player with a liking for bad food to one of the Scottish Premiership's best performers in 2015, one who will be involved against Qatar on Friday and more importantly against the Republic of Ireland a week on Saturday.

Griffiths said: "The manager had his reasons why he left me out. I had to go and work on aspects of my game and get fitter.

"That's why I'm playing now. It's not just one thing. It's getting stronger, working harder in the gym and in training, changing my off-field stuff, changing my diet. I've done all that.

"My personal view is that he didn't think I had it in me to do it. I'm thankful I've changed his mind with everything I've done. It's not just my diet. In Norway, there's a big thing about body fat.

"My body fat probably wasn't up to his standards. I've never been the fattest of guys over the years.

"I've tried to work on keeping my body fat down and not eat as much as what I should have been eating. I'm trying to eat the right foods.

"I was a sucker for fizzy juice - I have a sweet tooth for Irn-Bru - but now it's all about diluting juice and water."

It should be noted that Griffiths was drinking from a bottle of water during his chat with the press. Good lad.

He admitted Deila was concerned that his lifestyle would rob him of his career. Thankfully, the 24-year-old was ready to listen.

Griffiths said: "The manager made a comment about my off-field antics and what happened over the last few years. I think he just wanted me to change that.

"He said he saw potential in me and if I cut all that stuff out I could be a real top player. I think, since the middle of January, I've started to show what I really can do."

And how is the body fat now?

"I am not answering that," he laughed. "It could still be better. The manager said that before I left. I did get the body fat count down in the second half of the season because I worked hard."

The thing about Griffiths is that he's a nice guy and it can he hard to match up the amiable bloke happy to answer any question in a car showroom in Leith yesterday with the YouTube star.

Deila deserves great praise of getting the best out of this talented footballer who admits now that he knew the Celtic manager was far from convinced by him.

Griffiths said: "The way he was looking I guessed he was thinking that he wanted me to change, but didn't think I had it in me. I went out of that room after a meeting with him determined to get my place back in that team."

A turning point was when Deila, perhaps as a test, asked whether he fancied playing in an Under-20 match in Sunderland.

Griffiths said: "I remember that well. We had a team meeting on a Wednesday and the manager pulled to me to the side after it and said there was a game the next day and asked whether I wanted to play in it but that I didn't have to if I didn't want to. He gave me the option of training with the first-team.

"I told him that I would play because I needed games. I needed to be match sharp so I went down with the lads and we did really well to get a result."

It's that kind of attitude which has saved Griffiths' career.

He said: "I spoke to Neil Lennon about it last season when something happened and he said that if I wanted to be a Celtic player then I would have to put all that stuff down.

"I was disappointed when he left but the manager came in and after pre-season I obviously wasn't fit enough to be in the squad.

"And since October I haven't missed out on a squad.

"You can't be chosen for Scotland if you are not playing for Celtic. I had no problem not being in the squad but since the turn of the year I've hit a good run of form. I was disappointed to miss out on the last one, but I've got myself in now."

And he is no mood to let his place go now. Let's raise a glass of mineral water to that.