Rihanna called the Ryan Seacrest's show on Kiis FM on Thursday, where she talked about her recent weight loss as a result of the 5 Factor Diet.

That was a routine that I started, Rihanna said. The Five Factor Diet has gone straight out the window ever since I went on tour. I mean, it's difficult to have any kind of routine when your schedule is that crazy. I really have no idea how I am continuously losing weight. It is actually pretty annoying because now I don't have a butt, no boobs. I already had no boobs to start with. I am eating everything.

The 5 Factor Diet is the latest weight loss plan that has reportedly helped celebrities like Jessica Simpson, Eva Mendes, Alicia Keys, John Mayer and Kanye West get in shape. The book of the same name was written by celebrity trainer Harley Pasternak.

What Is The 5 Factor Diet?

According to WebMD, the five in the 5 Factor Diet results from the number of elements each meal should contain. They are protein, complex carbohydrates, fiber, fat, and fluids. Five is also the recommended number of meals a day along with recipes that have no more than five ingredients. The meals should also take no more than five minutes to prepare and five minutes of cooking time, WebMD reported.

Rihanna's father, Ronald Fenty, reportedly told a magazine that when he last saw his daughter he thought she looked fat and is glad that she is losing weight.

I actually thought she was a little fat the last time I saw her, Fenty told Heat magazine, as reported by the Daily Mail. But when I saw her at this year's Grammys, I thought she was back to her normal size. I used to joke with her, 'Robyn you're getting too fat.' But I think she's fine. I think she looked excellent, as everyone saw, at the Grammys. She's dieting, she's working out.

Can 5 Factor Diet Work For You?

WebMD reported that nutritionist Cathy Nonas, MS, RD, believes the diet has all the right things for a successful weight control for many.

This is a healthy plan that incorporates all the food categories in appropriate proportions, Nonas writes in her review of The 5 Factor Diet for the American Dietetic Association. The exercise is a combination of cardio and strength training, and you don't need any expensive equipment to do it.

Some said that while the diet is nutritious there are still some flaws.

Weight control psychologist Abby Aronowitz, PhD, director of SelfHelpDirectives.com, told WebMD that outside of the Hollywood community she doesn't believe there is any evidence to show that eating five meals a day is a secret formula to weight control. In the end, it's just calories in and calories out, and it doesn't really matter when you eat them -- and to try to convince us otherwise is somewhat misleading.