Everyone carries their weight different, and the effects on their body are different.
Certainly, if you add a substantial amount of weight in a short period of time, its going to have a big impact on your body.
But you have lineman in the NFL playing into their mid 30's and doing fine. And their mobility/agility/reflexes are even more important than a 1b in baseball. I really dont think Fielder's weight will be that big of an issue going forward.
This.
I'm a huge Prince fan so I'm biased. His dad fell off a cliff at 33, Prince will be 28 in May. Prince doesn't look as big as Cecil to me (baggy jersey could have something to do with it), and modern day MLB teams should have much better conditioning programs than anything Cecil was subjected to when he played.
Honestly, there are certainly challenges with a vegetarian diet and he could be a constant pizza eater for all I know, but I think his vegetarianism is an indication that Prince is relatively conscious about his diet and that his diet could improve as he ages.
As an aside, I hope the Nats employ really solid trainers and dietitians for these guys.
All in all, I don't find a long-term contract for Prince as risky as a few other contracts handed out this year by other teams, or even more risky than the one we gave to Werth last year, not that these should be bench-marks.