Today on Oprah, she and her staffers kick off the vegan challenge where they will abstain from eating any animal products for one week. Oprah tried going vegan before but went back to eating meat and dairy after three weeks.
I think it's much more difficult to sustain a vegan diet if your main concern is for yourself, that is, for health reasons. If however, you become a vegan to reduce animal suffering, then the lifestyle is much easier to maintain. When you make the choice that you will no longer be a participant in causing another sentient creature to suffer or to be killed unnecessarily, it becomes a guiding principle for all your choices and actions.
And as a beneficial corollary you may just find that you become healthier in the process...in both body and mind.