Why did Alphonse lose everything? In the show, whenever an alchemist commits the taboo, they only lose one part of their body. Izumi lost organs, Ed lost his leg, and Mustang lost his eyesight. But, when Alphonse tried to transmute the soul he lost his entire body. Even though the equivalent exchange was justified for the other alchemists, I can't help but feel like Al's was not equivalent. 

Can someone explain to me why he lost his whole body rather than just one part?
Alphonse was shown more of the truth than Edward, however he forgot it at the beginning of Brotherhood. Only towards the end did he remember. Thus, seeing more of it warrants a greater toll.

Also, the truth takes from you that which is most ironic (which is why it is such a cruel thing); for example, Mustang had his sight taken as he had his 'sights' set on being Fuhrer. Alphonse had his entire body taken as he wanted to feel his Mother's hugs and warmth. Having his body taken means that can't happen anymore.