Christina Aguilera banned "dairy and carbs" from her diet to lose weight.
The 32-year-old star had a number of small meals throughout the day, avoided dairy and carbohydrates products - both of which provide energy - in addition to doing "energy training" to slim down.
A source told Yahoo omg!: "Her diet plans has been built around very small portions and very high energy training for short periods of time, but frequently.
"Banned are dairy and carbs. On the agenda is a lot of coconut water, herbal teas, tofu, celery, oily fish and small amounts of low fat cheese.
"But the major key to this is only hand size portions of every meal and five small meals a day."
Christina's weight loss became apparent at the start of this year and her new figure helps increases her confidence.
The source added: "Her body is hugely important to her and it's one of the ways she gets her confidence - so being overweight was something she was never going to live with."