London, July 14 - Pop star Britney Spears has gained 14 pounds in just one month following a break in her world tour and is now under pressure to lose it.

'She was in tears saying they're calling her fat again. She showed up to a meeting with a latte in her hand and everyone jumped on her. Britney's supposed to be eating a diet of fish, chicken and vegetables. When she swaps the healthy stuff for junk, her dad gets worried,' contactmusic.com quoted a source as saying.

Spears' father Jamie, who became co-conservator of his daughter's personal and professional life following her breakdown last year, put her on a strict exercise and diet regime as he knows how important it is for her to look good.

However, Spears who has two sons - Sean, 3, and two-year-old Jayden, is struggling to stick to the health plan and regularly indulges in calorific treats.

'She doesn't think about the calories in the food, just that she likes it. She loves greasy food and creamy sweets and hates fruits and vegetables. She still eats a lot of fast food -- mainly late at night,' added the source.

The singer is currently rehearsing for the European leg of her Circus world tour.