Besides the specific genes that always remain “on” or “off” (so that a liver cell is a liver cell and not a kidney cell), there are also genes that are switched on and off in response to external circumstances, such as social contact, eating, or exercising. So engaging happily in sports or other physical activities sends different signals to our genes than does slouching grumpily on the couch. Of the hundreds of transcription factors, only one is of special interest to us: the nuclear factor kappa b, NF-kB for short. This factor underlies many very important biological processes, including how
...more

