What effect can a lactulose have on persons following the atkins diet plan?

Lactulose: Lactulose is a milk sugar, the atkins diet, or similar low or no carbohydrate diets recommend against dairy products as they contain fat and sugar. The point of the early portion of the diet is to use a less efficient metabolic pathway that burns fat or protein only. Eating sugars and fats may push you out of the ketotic metabolism into normal metabolism... So you would be thwarting the diet.

Lactose a laxative : Low carb ketogenic diet such as the Atkins diet often cause constipation in the early stages of the diet. Lactulose is a laxative that will probably help at the early stages but if taken at high doses can cause stomach upset and diarrhea.