Diet Tips

I’m doing some research on fad diets and trying to compile a comprehensive definition outside of the above. I’m confused since when I looked at a fad diet -i.e. 3day tuna diet – although limited, it consisted of vegetables, fruits, tuna, water, bread (obviously whole grain is preferred), tea, coffee. It’s not terribly unbalanced. The Blood Type Diet was another one listed, though I thought that was supposed to be alright. Can someone please clarify for me? I’m getting my info from http://diet.lovetoknow.com – it came up when I plugged in "fad diets" in www.dogpile.com search engine.