High protein, low carbohydrate diets like the Atkins diet and the South Beach diet are very popular. These diets can be helpful for diabetics and people with gluten intolerance. In these diets, protein and high fat foods are not restricted; vegetables are limited. The main difference between Atkins and South Beach seems to be that the South Beach diet is less structured and emphasizes eating healthier, mostly unsaturated fats.
The primary objections I’ve seen to these and similar diets — and this applies to everyone, not just nursing mothers — is simply the fact that they are not balanced and thus have the potential to make you feel unwell. These diets tend to be low in phytochemicals, antioxidants and folic acid. They also tend to be low in fiber and minerals (including calcium, magnesium, phosphorus & potassium), and the Atkins diet may be high in saturated fats. Because of this, long-term adherence to these diets may increase your risk for various health problems. Since some of the weight loss from these diets is simply due to water loss, dehydration is a risk if the dieter is not careful to drink plenty of water.