A commenter, Cynthia, pointed me to this entry from Devon Crosby-Helms:

I started reading a book called The Butcher and The Vegetarian and had a realization. The author was talking about her symptoms of fatigue and inability to lose weight no matter what she did. She was a life-long vegetarian and the solution: Eat Meat. …

I realized then that I needed to start eating meat again. I did, I felt better. Wahoo. Problem gone! Energy returned. Training gains achieved. I have the type of constitution that thrives off a diet consisting of fruits, vegetables and meats (and fats) and all parts of that are necessary for me.