"There are times when I want to quit because it's so much work," said Garth in Us Weekly's November 19 issue. "It's so much work and time away from my family."
Despite finding the "mental aspect" of the competition difficult, the 35-year-old former Beverly Hills 90210 actress has also seen the positives of participating in Dancing with the Stars fifth season.
"When I decided to do the show, I did Pilates three days a week and cardio twice. I hated it, but it helped," Garth told Us. "Once I started dancing, things changed faster than when I was just working out."
Garth said she's lost "about 10 pounds" since she began competing on Dancing with the Stars with professional partner Derek Hough and initially thought getting in shape would just be a "great perk."
"It's more about the inches and toning," Garth told Us, adding her legs now "look great." "My jeans were a 29 when I started and I'm wearing a 27 now. It's great to be able to go to the back of my closet and get the clothes I wore [pre-baby] and know that they're going to fit."
The mother of three said Dancing with the Stars is her 10-year-old daughter Luca's "very favorite show" and she encouraged her mom to participate. However it was her 13-month-old daughter Fiona who really helped Garth overcome her "hesitation" and join the cast.
"I wasn't in great shape when I started. I'd gained about 35-pounds in pregnancy [with Fiona], and I still had maternity weight to lose," she told Us. "I hate those women who lose weight quickly after having the baby! I'm not that way."
Because Fiona's September 2006 birth came when Garth wasn't working on-camera, she said she wasn't "under pressure to get back in shape quickly."
"I have the kind of body that once you start exercising, it responds," she told Us. "The biggest surprise is probably my comfort with my body. That I can go out there half-naked. It's very revealing."
While Garth said she's been eating "a lot now" because she's "always hungry," she added it's not a big issue.
"I'm just burning through it. Now I can eat and not worry about it," she told Us. "I definitely feel great and I have a lot of energy!"
Still, Garth said it can be tough to look at the sculpted physiques some of the Dancing with the Stars professionals flaunt.
"It's hard not to admire Julianne Hough's body. I look at her and think, 'What a nice little tushy!' And then I have to remind myself that she's 19," Garth told Us. "The guy dancers all have great bodies too. They don't have any body fat. And they love to show it. They can't get enough of themselves in the mirror!"
Garth has previously stated her husband -- actor Peter Facinelli -- has been supportive during her Dancing with the Stars experience, and she's apparently repaid the favor with her newly toned body.
"He really likes it," she told Us. "He said, 'It's like I got a new car!' He can't keep his hands off me. To the point that it's like, 'Enough!'"
Garth is aware her Dancing with the Stars experience could come to an end any day now -- but either way -- she's glad she took the opportunity to participate.
"I love just watching to see who gets voted off -- even if it's me! It's a journey, and if it's over, it's over," she told Us. "It was fun. My real life is fun too. So I'm happy to go back to that!"