
Apparently Japan, and now Korea, have gone ape over the banana diet, causing banana shortages in Japan. The gist of the diet is basically this: eat a banana and warm water for breakfast, then eat a normal lunch and dinner.
To be honest, it's not a bad idea. Bananas are good for you, provide lots of important nutrients, and ensure that you start off the day in the right way. And, it's easy. For people who don't like eating breakfast, a banana is fast, portable, and palatable.
The problem is with the "theories" behind the diet. In an article on the diet, the rationale for why the diet works was that bananas are easily digested and allow the stomach to "rest longer." It went on to say that foods that are more difficult to digest cause the entire body to tire out, making the body prone to weight gain. This is laughable and twisted science.
It is true that complex carbohydrates like vegetables, whole grains, and proteins are more difficult to break down and assimilate; however, this digestion actually provides for a greater calorie burn, and enable you to feel full for longer. Your body and stomach were designed to accomodate the digestion of complex foods, so the idea that this would tax the body too much and lead to weight gain is completely fabricated.
That said, eating bananas for breakfast is a reasonable diet plan. Bananas are healthy, provide important nutrients, are low in calories, and are filling. They also come in "prepackaged" portions that prevent a person from over-consuming. It's no wonder that people subscribing to this plan would successfully achieve weightloss, it's just not for the reasons that the diet describes.