It's a bit anecdotal, but the people that I have met who are vegan / vegetarian are a heck of a lot healthier / in better shape than most of the people I know who eat meat. A lot of Indians don't eat meat (possibly inherited culturally from Hinduism) and I work with several who have engineering Ph. D's from good universities and don't seem to be mentally held back by their diet. Personally, I still eat meat, but I'm trying to cut it out of my diet as much as possible. I never really enjoyed food that much to begin with so it's not hard to do. For example, every morning, I start my day with a smoothie containing almond milk, greek yogurt, kale, spinach, cabbage, carrots, and frozen mixed berries including strawberries, raspberries, blackberries, mango, pineapple, and peaches. If I'm feeling really hungry, I'll add oatmeal or eggs. I eat that every day as my breakfast and never get tired of it. The hardest part has been giving up ice cream, but I limit myself to only one serving per week. Plan to eliminate it completely eventually. Diet is one component of health, the other part of diet is calorie intake. The only known way to increase lifespan is calorie restriction and although it works well in chimps, not sure how well it works in humans.
During the springtime, my cat regularly brings home something to eat at least once every couple of days. I'm sure he catches a lot of prey that he does not bring home. He kills for sport, but sometimes will eat the animal. I feed him well, but once saw him eat an entire mouse -- head, tail, and all. Probably about a quarter to half the time, he'll eat the animal if I let him. Twice he has caught a full-grown rabbit. I wish I could get him to stop hunting and he will eventually become an indoor-only cat. He's just not ready for that now.
