By Richard Bath for the Daily Telegraph

There came a moment this northern summer when Stuart Hogg realised things had to change. It wasn't when Conor Murray inadvertently fractured his eye socket, ending his Lions tour before it had even begun.

Nor was it when he was coming to terms with the arrival of a second child, an event which forced him to re-evaluate how much time he spent helping out on the home front.

Instead, the moment that made the Scotland full-back reassess his life was when he was an usher at team-mate Duncan Weir's wedding in July.

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On the morning of the wedding, he went to pull on the suit which had been specially made six months earlier and realised he couldn't stretch the waistcoat over his burgeoning frame. He had been aware that a love affair with Guinness was taking its toll, but this, he said, was the final straw.

"I was sick of seeing photos of how fat I was getting, so I decided to shed a few pounds," he said.

"It was mainly after the summer. I knew I was getting a shoulder op and I had the potential to balloon.

"I actually took the decision at Duncie Weir's wedding in July, where I was an usher, and I was struggling to get the jacket shut from the measurements taken six months earlier.

"It's made a difference in terms of how I look and how I play but also in terms of life in general, which makes it sound like I've been in rehab!

"I lost about nine kilos and then managed to put a couple back on when the shoulder was building back up again.

"I was quick last year but now it's roughly similar scores but more consistent and I feel I can go for longer as well.

"I'm never going to be a guy who can run over the top of people so I need to be in a position where I can go around them or step them. I also did a lot of speedwork when I was injured and hopefully that will help."

Hogg has played only two games for Glasgow so far this season, but he has been in pin-sharp form in both, and his club coach, former Chiefs boss Dave Rennie, has certainly been impressed.

The Kiwi recently spoke in glowing terms of Hogg's remarkable speed after the full-back broke the club's straight-out sprinting record, hitting 36.8kmh - just over 10 metres per second - to eclipse past Warriors speedsters such as accomplished sprinters Thom Evans and James Craig.

Hogg says that giving up his guilty pleasure of Guinness, losing 9kg and then maintaining his target weight of 92-94kgs has added an edge to his game.

"I wanted to make a difference and I thought that I had been a couple of kilos too heavy over the last few years," he said.

"It just happened that I managed to lose a lot. I feel comfortable at this weight and feel I can do more damage at this weight."

If the main effects of losing almost 10 per cent of his body weight are physical, he says that his new approach has also bolstered the mental side of his game.

Transforming his physique may have made him feel happier about seeing images of himself, but it was also part of a process where he sat down and consciously asked himself what he wanted to achieve from this season.

"Losing weight has meant a lot of different things, including [feeling better] looking at photos," he laughed.

"We were asked individually at the August camp what we were going to do to make this our best season and I just wanted to see if that would make a difference.

"I feel I can go longer and have a bigger influence on the game."

Incredibly for a professional athlete, Guinness was not the only vice that Hogg felt was holding back his game.

"It seemed that the takeaways were taking over," he says of his decision to seek nutritional advice.

"In taking on the challenge to stay at this weight, I now know exactly what I have to eat and drink and all the supplements to take.

"The biggest thing was learning about all the foods to eat, but there are a lot of factors - it's just being more professional about everyday life as opposed to just when you're in playing rugby. I feel a lot better for it."

Hogg now has a strictly regimented diet that he polices himself.

He and his wife Gill prepare the raw ingredients for the week ahead on Sundays, and then Hogg takes on the cooking duties "so we're not just getting a takeaway if we can't be bothered to cook".

Asked whether such a regimen should be second nature for a professional sportsman, and whether he had received much advice on the subject, Hogg just nodded his head before replying: "Yeah, I just wasn't listening."