Does he drink pop? Coffee? Caffeine was a big trigger for me pre-Paleo. (It's fine now, for whatever reason.)
Other triggers from my "three migraines a week" days: MSG, sugar (too much or too little), back/neck problems (fixed by lifting and posture), allergies to anything and everything outdoors (also gone). Has he tried eliminating these and other common triggers? Also, does "red meat" to him mean "gas station beef jerky"? It took me a decade of my life to get my triggers down, and even then I would occasionally get migraines for seemingly no reason. Never, though, have I heard of red meat being a trigger.