Don't forget you can "can" your own meats & control ingredients that way... The Ball Blue Book tells you how to can common meats & stews etc. with a pressure canner.
Yes the MRE meals have that many calories...they were designed to support highly physically active soldiers doing their work (hard physical labor!!). The website in karlsgunbunker's post above mine has lots of info on it, you might want to check it out, it is awesome for MRE info.
i dont think ive ever gotten more than 3 or 4 hundred out of one though...most of the meal tastes like vacuum sealed feces...i pretty much stick to the crackers and jalepeno cheese...its amazing how long you can live off just that.
Also, just remembered, you can get Mountain House freeze-dried hamburger in #10 cans now from Nitro-Pak (**new item**)...but it is made w/ sodium (650 mg per serving) . Also different brand available at Emergency Essentials but theirs has less sodium per serving (380mg)
To get unsalted freeze-dried meat, looks like you have to get the raw ones, like the #10 cans of F.D. Pork Chops from Mountain House.