When Britney Spears hit the beach in the Bahamas on May 20, one thing became clear -- her body is back in top bikini-baring shape!

Britney, 27, "can be lax with her dieting," explains a family insider, who says the star is basically relying on dancing onstage to keep her fit. "She indulges in comfort food and fast food and then retains water."

But she also notices when her body-hugging costumes are bulging and promptly switches to weight-loss mode. "When the bloat's showing," says the insider, "she starts watching what she eats, cutting back on sodium-heavy food and caffeinated drinks to get things under control."

For more on Britney and other stars' dieting secrets, pick up the latest issue of Life & Style, on newsstands now!

Credit: Courtesy of Candies