That I was slim with a "high carbs" diet for 20 years also makes me doubt the carbs theory a bit. There seem to be other factors. I exercise less, but there were stretches of time when I didn't exercise a lot, too. My wife having a baby gave a big boost to my waistline, too. Might even have to do something with hormones (men's hormones change during pregnancy, too)?
I've also heard that changing one's diet in any way is likely to cause weight loss at first, so I'd be careful with evaluating anecdotal evidence.
I'm curious about the energy aspect, just wish there was another way. The thought of eating 4 eggs for breakfast makes me sick. I just feel repulsed by eggs and meat most of the time.
I actually have a hypothesis that human digestion might be very adaptable. Humans managed to hold on in very diverse environments, from the arctic to the desert. Presumably they had to dwell on different kinds of foods depending on the environment. So it makes sense if digestion can adapt to a huge variety of food. Might be that industrial food is a main culprit after all (lots of sugary foods that have only been around for about 100 years).
Another thing: how did people manage to eat the equivalent of four eggs for breakfast in paelo times? I've read that gathering was more effective than hunting, so presumably they had more vegetables and fruit than meat on average?