In this articlePFEMTSRThomas Fuller | SOPA Images | Lightrocket | Getty ImagesA version of this article first appeared in CNBC's Healthy Returns newsletter, which brings the latest health-care news straight to your inbox. Subscribe here to receive future editions.Pfizer's newest bet on obesity is already showing promise. The company last week said it would buy weight loss drugmaker Metsera in an up to $7.3 billion deal, including future payments, that is expected to close at the end of the year. Just a week ...