Is high metabolism good?

Sometimes low-fat blogs, like Dr. Fuhrman's, publish some interesting posts. Like this one on low thyroid activity being tied to longevity. He cites several studies like "Low serum free triiodothyronine levels mark familial longevity." Basically they show that in families with a large amount of unusually-long lived individuals, average TSH is higher.

But wait...don't we want to boost our metabolism, lose weight quick, OMG111!!!? Depends on your goals perhaps. If the only problem you have with a underactive thyroid is more weight than you would like, perhaps it's not worth altering.

Looking at my family tree, average age of death for women even in the 1700s was 70. Currently I have several nonagenarian (over 90) female relatives. My maternal grandmother at over 90 has zero health problems. She's never been a skinny gym rat, but she's always walked places as much as possible. I remember my mother always giving her a hard time for not eating breakfast and she has confessed to me that she sometimes eats a chocolate bar in place of a meal. Growing up during the depression, her diet did include organ meats and raw dairy. I suspect that genetics accounts for some of my grandmother's health, but early childhood nutrition is very important too. As far as I can tell that's what separates the healthy people in my family from those who struggle with health problems.