http://atkinscenter.com/Archive/2001/12/13-162534.html

Q: What effect will Atkins have on liver and kidney function?
A: There are no studies showing that Atkins causes kidney or liver problems in healthy individuals. There are research trials that looked at liver and kidney and heart function, with participants on ketogenic diets similar to the Atkins approach in which no negative effects were observed. Also, when we did a follow-up of more than a year on patients at The Atkins Center for Complementary Medicine, including checking their kidney and liver functions, there was no adverse effect. Of course patients in kidney failure are extremely restricted in everything they consume, including water, so Atkins would not be appropriate for them.