You would think, but it seems like players in the past who were notorious for being fat or heavy and had a lot of power, who then went on to lose weight and get in better shape before a season, would often have lower power numbers. But then again I'm only really recalling Prince Fielder when he took on that vegetarian diet after his 2007 breakout year, lost weight, and then lost over 100 points to his SLG and OPS, so I really don't have a lot of frame of reference. There haven't been a lot of "fat" power hitters out there. Off the top of my head I can only think of David Ortiz, Mo Vaughn, Cecil Fielder... and I'm drawing a blank now. Do you have any examples of people who have actually lost significant weight and seen a noticeable power decrease? Only one I know off the top of my head was the Fielder situation, mostly because it became a topic of conversation throughout the season when he stopped hitting home runs with the frequency he had hit them the year before (when he had 50). There were a lot of "Should Prince fielder start eating meat again?" articles, IIRC, which is kind of hilarious.