The Idiot-Proof Diet is not safe because it doesn't recommend enough carbohydrates for proper brain function and because the scarcity of fruits, vegetables, fiber and dairy in the diet may induce constipation, according to a review of the diet by the Academy of Nutrition and Dietetics. The book's authors also recommend feeding children the same way, which may be even more detrimental due to the diet's effects on brain function.
Part of the risk to proper brain function is due the number of times Phase One of the diet is recommended, explains the Academy of Nutrition and Dietetics. This is the phase that limits dieters to 30 grams of carbohydrates per day, but the Institute of Medicine recommends 130 grams per day for brain function and health. This phase is repeated six times over a period of months, and while the diet encourages cheating when necessary, it recommends returning to this phase afterwards, further increasing the period in which dieters receive inadequate carbohydrates. One of the effects on brain function is a severe headache, which both authors experienced. Recommended numbers for carbohydrates and other amounts are not based on any scientific research but on the personal experiences of the two authors, so the advertised effectiveness of the diet may vary, according to the Academy of Nutrition and Dietetics.