Six months ago, I would have agreed with you Anguish. After watching the documentary "Forks over Knives" and then backing up the claims in it by reading The China Study and multiple writings by nutritionists and doctors, I am sold on a whole-foods, plant-based diet (I don't use the word 'Vegan' unless I'm trying to order at a restaurant). I don't want to save the whales, and I'm not even against eating some chicken or fish now and then. I'm still planning a nice prime rib on my birthday.
There is an ever increasing amount of empirical and scientific data to back up the concept that animal based products are not good for your overall body health. I didn't 'give up' anything. I started increasing my intake of nutrient-dense badass superveggies (Kale is one of my favorites) and found that other foods didn't 'feel' right anymore. Your body will let you know how it feels about your dietery selections, you probably just haven't been paying attention (If your bowel movements could set a record at the NFL combine, you're doing it wrong). Over time, I just decided that an apple sounded better for breakfast than a doughnut because I didn't feel like shit after I ate the apple. I can still eat doughnuts, I just choose not to 99% of the time.
I'm going to give dairy it's own paragraph here because I think it's up there with sugar among the worst things you can put in your body and it gets pushed as a healthy food choice by the American media constantly. Just think about the purpose of cows milk for a minute. A baby cow is born and it drinks milk as it's sole source of nutrition so it can go from being a 60lb baby calf to a several hundred pound cow that can feed itself. When it's big enough to feed itself, the cow doesn't drink milk anymore. So unless you're planning on quintupling your bodyweight over the next year or two, dairy products should be extremely limited in your diet. Dairy also promotes the growth rate of cancer cells btw. If you're going to do it though, look for organic, grass fed dairy products.
This is getting stupid long, so I'm going to keep this part short. Organic is a must for most foods. GMO's are bad, duh? At the very least, google "The Dirty Dozen" for veggies and buy those organic (Potatos and Apples are consistently the top 2 but it changes every year). If you've ever seen a cow farm (a meat farm, not a dairy farm) it's gross as hell. They are packed in like sardines on a packed dirt (no grass) patch of land and they just dump corn mush on them to feed them. Chicken farms are nasty too. Get free range, air cooled chicken (if it isn't air cooled, it's been cooled in a big vat of water and chlorine).
We had a whole thread on sugar here a few months back. Google 'Sugar the bitter truth' for a sciency video about sugar. The guy in that video also has a book out, I forget the name at the moment, but it covers a lot more and tones down the science to a more layman level.
Absolut, totally get you on the 'moderation' line man. Moderation doesn't mean you can have a little bit every day it just means you can enjoy a treat once in awhile and if you're taking care of your body correctly, meaning your waste handling mechanisms aren't all jammed up from eating an American Diet, then your body can process that load just fine (pun intended).
TL;DR Go organic, don't eat dairy, limit meat intake, sugar is bad.
P.S. I can't speak for powerlifting because I don't think that's a natural function of the body, but there are several Vegan/Vegitarian MMA Fighters that don't seem to have trouble getting enough of what they need from a plant-based diet. Link
President of the Perfect Parents Society - est. 2013