Although Low-Carb diets might be great for losing weight, it is doing a number on your breath. Low-Carb dieters have begun to suffer from persistent bad breath. It is not due to a lack in oral hygiene, though. In fact, bad breath while on a Low-Carb diet is a perfect indication that your body is burning stored fat.

According to the WebMD News Center, “Bad breath in the low/no-carb arena is often caused by certain chemicals that are released in the breath as the body burns fat. They are called ketones, and entering into a fat-burning state of ketosis is the hallmark of the Atkins diet.” So the good news is that if your breath is stinky, you're probably doing an excellent job of sticking to you Low-carb diet.

Doctors say there is no amount of brushing, flossing or tongue scraping that can rectify the problem because it is an effect of the fat burning within your body.
Diets that are extremely strict with the amount of carbohydrates you consume are mostly guilty of causing this side effect (Atkins).

Diets that allow you to eat more carbs are less likely to give you bad breath (South Beach Diet; Curves). Some ways to combat bad breath is drinking lots of water (which aids in breaking down ketones that cause it), chewing parsley, sucking on sugarless mints, or chewing sugarless gum.