Seems tree girth and a person's belt size are similar. For one, size usually increases in increments over time. Scientists don't usually core dead people for age approximation, but maybe that's because so many of us (at least in the United States) have medical records. Phillip Lopate says "the mental image of one's body changes slower than one's body" and that is something I can really relate to. I have gained lots of weight at once, and thought of myself as still relatively slender. I am much happier now that my mind has caught up to this. For trees, some years they grow an inch all around, while other years they only grow a miniscule amount. I suppose circumstances of rot could be comparable to weight loss or anorexia. Whether in trees or jogging pants, a decrees in girth is more rare. People rarely put on 100 pounds in a single year like I did when I started taking medicine, but I am certain even fewer of us loose those layers at our waste.