Common side effects of the Atkins diet are muscle weakness, cramps, diarrhea and headaches, according to WebMD. All of these side effects are quite common with carbohydrate deficiency. Fatigue and constipation are also potential side effects, notes Mayo Clinic.
Another potential safety issue with the Atkins diet is that because the dieter is so far below the recommended daily allowance of 150 grams of carbohydrates, the brain itself suffers from insufficient glucose. The side effects of constipation, diarrhea and nausea may result from nutritional deficiencies, including insufficient fiber, due to the extreme carbohydrate restriction inherent in the Atkins diet, explains Mayo Clinic. In the first phase of the Atkins diet, dieters eat less than 20 grams of carbohydrates a day, which can place the dieter in a state called ketosis. Ketosis can also cause mental fatigue, bad breath, nausea and headaches.