If you're on the Atkins diet, the good news is that you will probably lose weight in the first six months or so. The bad news is that you could start suffering from headaches, muscle weakness, diarrhea or constipation if you aren't already.
Bad breath happens sooner and, for Atkins, was a sign that the diet was beginning to work, and was burning fat stores.
But all these symptoms are classic signs of carbohydrate deficiency, says Danish obesity expert Dr Arne Astrup who has surveyed 60 studies of the Atkins and similar low-carb diets. The Atkins diet in particular shuns all bread, pasta and most fruits and vegetables.
Detractors argue that this proves that the high-protein, low-carb diet is ultimately bad for you, while those who exalt it say that it is a price worth paying in order to shed the weight.
Despite the side effects, many more are able to stick to the Atkins-type diet than those who follow a low-fat regime, Astrup's survey reveals.
Astrup supports the supposition that the Atkins diet works because people feel more full on a high-protein diet and so, in reality, are eating less and taking on-board fewer calories. But he believes that it is a dangerous diet in the long run. He says that the bad reactions, such as muscle weakness, are a sign that something is wrong.
"We have known for many years that there is a minimum intake of carbohydrate necessary to maintain the normal function of your body and that is approximately 150 grams a day. But, if on the Atkins diet you go down to 20 or 30 grams in the induction phase, then maybe go up to 100 grams, still you are far below what your body needs," he says.