I agree that extended fasting may reduce metabolic rate perminantly, or at least more perminantly, but intermittent fasting really doesn't provide a long enough fasting window to perminantly damage the body. For thousands of years humans had to cope with terms of fasting. Not for long periods of time over 48 hours as Dr. Phinney says. Humans evolved around short periods of fasting while they searched for quality nutrition. It would make sense that humans should then have evolved to thrive in their environment of short fasts between finding food.
I would probably agree with Dr. Phinney in his thinking that long periods of fasting are probably unhealthy. This really doesn't start cropping up in humans until long ceremonial and religious practices started to spread. All in all, old data really isn't always the best as @hashchash said. I would definitely like to see some new work on this. Old data just wasnt heald to the same standards as we currently operate under in the medical field.
Great Post! Resteemed!