I have had that happen, too, and drinking some water made the pain go away and made my urine less strong.

If this doesn't go away quickly, you should see a doctor.

Actually, that sounds like a UTI - Urinary tract infection. Sometimes it can travel really far up the ureters and feel like kidney pain, I had that a couple of months ago. Definitely go the doctor route! And keep drinking HEAPS of water to flush it out.

I don't know what's causing your pain, but ketosis and concentrated urine are both risk factors for kidney stones, so I urge you (as others have done) to drink more water.

You need to drink more water in ketosis to avoid kidney stones. You probably need to drink substantially more water than you are. If your urine is dark yellow (and you haven't been supplementing B vitamins and the like) it means you're dehydrated. This isn't a matter of "stressing" the kidneys, it's a matter of not taking in enough water to keep the kidneys flushed and prevent various acids and minerals from staying too long and forming stones.

drink water immediately and it will help within minutes, literally. but that's a bandaid to an sympton ailment that you are feeling because your kidneys are complaining.

personally, i've had several kidney stones before going paleo. i know exactly what that feeling is like (waking up with kidney pain). my stones were always calcium oxalate. chris masterjohn makes an extraordinarily strong case on the WAPF website about the role of fat soluable vitamins A,D and K playing a huge role in how your body distributes and absorbs calcium. so basically the fermented cod liver oil and high vitamin butter oil blend could play a major role with kidney function and calcium.

for the last 6 months, I've been taking that combo and I have noticed a huge improvement. now, i also completely changed my diet to lacto-paleo, but I pretty much never have kidney pain anymore and I haven't had a stone since. also, ironically, since switching to paleo, i drink much less water and yet still no kidney pain, almost like there's nothing there is no longer any calcium oxalate to 'flush' anymore.

hope that helps, jack k