The Belgian striker has returned to the San Siro on loan from Chelsea, only a year after moving to Stamford Bridge for just shy of £100million.
Lukaku struggled for form in the 2021/22 season, netting just eight Premier League goals for the Blues.
As a result, he has now returned to Italy, having revealed he was in contact with Inter manager Simone Inzaghi 'all last season'.
Upon arriving back for pre-season training with Inter, it's reported by Gazzetta dello Sport that Lukaku will now begin an 'immersive and ambitious programme' to get back into top shape for the new campaign.
They claim that the 29-year-old is returning to a personalised Mediterranean diet which features keystones such as chicken, sweet potatoes and black rice, but no traditional pasta.
Remarkably, Lukaku's target weight is reported to be 101kg, which translates to 15st 12lbs 11oz (or 222.7lbs).
This is heavier than boxing's reigning WBA, IBF and WBO heavyweight world champion Oleksandr Usyk weighed for his title-winning fight with Anthony Joshua last year.
Usyk has competed for most of his career at the cruiserweight limit of 14st 4lbs (200lbs).
More recently though, he has boxed at heavyweight and scaled 15st 11lbs 4oz (221.25lbs) for the AJ fight.
Therefore the weight considered to be Lukaku's prime condition is 1.5lbs higher than that of the unified heavyweight king.
For Inter, the season begins away at Lecce on August 13 - this is the target date for Lukaku to complete his body transformation.
And for Usyk, his rematch with Joshua is scheduled for the following week on August 20 in Saudi Arabia.