I recommend that anyone on a low carb diet, (particularly the Atkins), consider taking a a plain filtered tapwater or warmed bottled water cleansing enema every day while following the diet.
It will go a long way toward eliminating the headaches so many people report while on these type diets. When you are eating a large proportion of protein, your system is dumping excessive amounts of ketones and other harsh chemicals into your liver and from there into your large intestine, and plain water enemas dilute them and help wash these toxic wastes from your system.
Occasional professionally administered colonics (weekly to monthly) can also work wonders.