The 22-year-old actress has given up smoking and drinking alcohol and has been spending countless hours in the gym, reported Showbizspy.
"Kristen has barely touched alcohol since July. She has given up smoking and taken up Bikram yoga. The new fitness plan has done wonders for Kristen's body and mind. Even her skin is glowing," a source said.
"Robert just couldn't stop raving about how fantastic Kristen looks. And she is telling friends that she is going to reel him back in with her body," added the source.
The couple has reconciled following their split. They had parted ways when it was revealed that Stewart had a fling with married director Rupert Sanders.
Friends don't believe that this reconciliation is going to last.
Reports claim Pattinson, 26, has issues trusting Stewart.
"The love story between Robert and Kristen is still a bit of a conundrum, it is a weird relationship. Despite claims that all is rosy, he is still not completely convinced that giving their relationship another chance is the right thing to do," a source said.
"There are moments when he continually asks her questions about the affair, so it is all still very tense. They have some really serious trust issues," it added.