Doctor Kellogg was such a colorful character that this could be the largest section of the website if I got into telling stories about the guy. But I shall resist, simply tossing out a smattering of items that may be of interest.
The Notes book is more about the family—and especially his half brother, Merritt—than it is about John Harvey. Still, it does give some biographical background, and is a fascinating read in its own right.
In some ways, my favorite depiction of Dr. Kellogg is that provided by Dr. S.P.S. Edwards in his Memoirs. Since his account covers so much more than Kellogg, though, you will find it in the "General Miscellaneous" category.
Item #7, a colorized photo of Kellogg, shows him with reddish hair. Not to make too much of the matter (my wife does not appreciate redhead jokes), I would have thought that someone would have mentioned it if he really had red hair, but I've never seen it written. If you know anything about this, send me an email, please. It's not important, but it is intriguing.