PARIS, France -- As the new streamlined Billy Vunipola pondered what food he had to cut out in his new fitness regime, the conversation turned from pasta to jelly babies. When Vunipola runs out in Paris on Saturday evening, he will be at his optimum weight of 130 kilogrammes, eight less than he weighed at the start of a gruelling summer of training.

Routines had to be changed and habits altered. He now has to eat the interloping vegetables and salads where before they were mere decorations on his family table.

"If you ever go to a Tongan meal you would never see salad on the table," Vunipola said. "If it is there it is probably the flowers decorating the table."

It has not been easy for the No.8. He was dropped during the last November series due to a loss of form and had to watch Ben Morgan jump ahead of him in the back-row pecking order.

Then came Morgan's leg break in early January and a refocused Vunipola took back the No.8 shirt for the Six Nations. He was singled out by Andy Farrell in the last press conference of the championship as having been a standout performer.

Vunipola has an appetite for improvement. His summer has focused around harnessing his power and working on his fitness. "I wouldn't say I've enjoyed it but we got through it. It's helped me improve my physical appearance and getting around the field."

However, with fitness gains have come sacrifices. "There is always temptation, but I think what has helped me a lot is my knowledge.

"I never used to think that bread was bad for you or pasta - even jelly babies! I thought they gave you energy! I guess if you eat too much of those you put on weight, so that's helped me a lot. My knowledge and knowing the types of food and what to eat [has improved]. Even portions as well."

Billy Vunipola during England's Captain's run at the Stade de France© David Rogers/Getty Images

Visits to his parents' - Singa and Fe'ao - house now occur outside of meal times so Vunipola can "try and keep it safe" when it comes to eating but foregoing those opportunities are all part of the new Billy.

Come Saturday night in Paris, Vunipola will be hoping to showcase the benefits of his new thinner frame. He will have added an extra yard of pace to his game but will still pack a firm punch in helping to get England over the gainline.

"I don't think there is anyone else who is 130 kgs in the back row. Hopefully I will be faster and more explosive and I don't lose that side of my game. I also want to be able to get over the ball and not be easily moved. Little things like that.

"I guess I have a big challenge against France to win the approval of not only the coaches but those beside me playing and to try and force my way into the squad. I guess the cut is coming soon and we all know that. It's a massive challenge for us to back up what the boys did last week in this game and hopefully get a margin between us and them."

Following Saturday's match, Vunipola will weigh up his own performance but allow a brief moment of temptation when he has his weekly 'cheat meal'. It will be well earned.

"I vary from week to week. If I see someone eating pizza and it looks like nice I'll probably have a pizza. The same goes for a curry. If we're watching a movie and someone's eating a curry then I'll have a curry. I'm not one to close down the options. I'm open to whatever is going that week. I'm pretty easy."