There is one factor that holds undeniable weight in any account of Leo Messi's transformation from last season to this one: his physical shape.

The Argentine's resurgence this term, in which he has scaled heights that many thought were now beyond him, is inextricably linked to a strict diet.

Giuliano Poser, a nutritionist based in Sacile, near Venice, has provided the ingredients to get Messi back to his best. Since the pair have been working together, the superstar has looked noticeably slimmer, losing between four and five kilos.

Conscious that injuries and not taking good enough care of himself had stunted him in 2014, Messi has paid more attention than ever to his physical condition this season. The forward has become a different beast, gaining a yard of pace compared to last year and, almost as importantly, extra strength that enables him to withstand defenders' attentions like never before.

Messi has become "unstoppable", as Pep Guardiola would say, even when holding up the ball with his back to opponents.

So effective has Messi's metamorphosis been that the 27-year-old has convinced some of his Argentina teammates, including Luciano Vietto and Sergio Agüero, to visit Dr Poser ahead of next month's Copa América in Chile.