The 'Your Body' singer - who recently shed 20 pounds - has completely changed her diet and feels great but allegedly wants to regain the figure she sported in 2010 by using a meal delivery service.
A friend close to the 32-year-old star said: "She did it all on her own. She goes online and picks out her food.
"She's been working hard. She wants to lose a bit more. But she feels great."
The mother-of-one also recently started doing a lot more working out, and reportedly loves yoga.
The source added to US Weekly: "It's more of a mind-body thing for her. She believes in exercise that she enjoys, doing strength work as opposed to cardio."
Christina ditched her favourite fried foods and was inspired to adopt a healthier lifestyle after becoming depressed by critics, who called her "fat" last year.
The source said: "A lot of people were on her about her weight and it depressed her. She went through a bad time because of the criticism."