England prop Mako Vunipola has revealed head coach Eddie Jones advised him to watch his weight in the summer ahead of the autumn home Tests.
England beat Australia 3-0 in the June series down under but Vunipola says players were sent letters to keep them "on their toes".
"My interesting bit was don't eat too much, to lose some weight," he said.
England play South Africa, Fiji, Argentina and Australia at Twickenham starting on 12 November.
Saracens player Vunipola, who has 35 England caps, said he limited his weight gain to only half a stone, and added: "I was expecting worse so it was all right.
"I got a letter through saying I'm in contention…. I'm happy to be in contention.
"Eddie likes to keep us on our toes - everyone got the letter reminding them of what they need to do."
New Zealand-born Vunipola is part of Jones' 45-man elite squad for the four-Test series, which starts with a fixture against the Springboks - the final squad will be announced on 26 October.
He will face competition from Harlequins' Joe Marler, who ruled himself out of the Australia tour saying he needed rest after a summer laced with controversy.
The 25-year-old was suspended for two weeks for kicking Grenoble's Arnaud Heguy in April, directly after serving a two-match ban for calling Wales prop Samson Lee "Gypsy boy" during a Six Nations game.
"Having Joe Marler back in the squad is a bonus," Vunipola said. "He's a good guy, I play some cards with him. He is in good spirits.
"Joe didn't really change during last season, he kept his private life to himself. He's the same Joe as usual."