Whether you're a K-pop girl group diva or a boy band hunk, there's little room for slackers when it comes to physical fitness for idols.

But how do South Korean pop stars stay so thin? For the members of Nine Muses the answer came in a paper cup.

The girl group's daily meal plan includes one paper cup filled with fruit, one with rice and one third side dish at every meal, according to the website Soompi.

The girl demonstrated the diet on Tuesday's episode of the South Korean television program "Star Beauty Show."

The ladies of Nine Muses pointed out that it helps you keep track of portions, but also alleviates the stress of the "one food diet."

Last year band member Sera spoke out about her personal difficulties in sticking with one-food diets.

"I tried one food diet and sometimes just starved," the Nine Muses singer told the website Fan Pop.

"After suffering from the yo-yo process and the stress of it, I'd go on a binge out of disappointment. That soon began to affect my health and made me prone to anemia, which made me realize that although I could lose weight with the help of pills or shots, I'd go through the yo-yo process no matter what."

Sera said that exercising regularly made all the difference.

"After I began exercising, I found myself having more strength during rehearsals and my body just began to feel lighter overall."

Minwoo of the seven-piece South Korean boy band 100% says that his band went through their own struggle to acquire their new physiques.

"For four months, we only ate chicken breasts, bananas, almonds and sweet potatoes for our daily three servings," the singer told NewsEn.

"There were times when we were so sick of it that we would just starve."

But when he and his bandmates saw the result of all their dieting, he recalled, they all realized it was worth it.

"When we saw that our bodies were changing, we finally felt great and that it was worth it. We liked how our bodies reflected from the mirror," Minwoo said.

"You have no idea how angry we were when people claimed we Photoshopped our bodies. We really earned it with difficulty."

And although the boys of 100% may not be measuring out their meals in paper cups, they get downright scientific when it comes to body fat.

"Our weight is the same, but our muscle mass increased," Minwoo said.

"Sang Hoon has the lowest body fat percentage. I think it's about four to five percent. We definitely have more self-confidence than before. We feel great and it's fun going to the public bath."