Rotation diets are necessary for patients with multiple allergies because if you have overt allergies to many foods, it is likely that you have slight, subclinical allergies to many other foods that you consider safe. Eating them on a rotated basis reduces your exposure to them and hopefully will help preserve your tolerance for them. Doctors prescribe rotation diets of varying degrees of strictness depending on the severity of your allergies. On the most strict diets each food is eaten only once on its rotation day and the length of the rotation cycle may be much longer than four to five days. One very allergic person I talked to had been put on a one food per meal, three meals per day, twelve day cycle diet by a prominent allergy clinic.
Some doctors consider rotation diets with very long cycles to be counterproductive.
For most patients, a four to five day interval between eating foods gives the best masking of symptoms. However, there are patients who find that some foods agree with them better if they are rotated at longer intervals. I personally have many foods that I can tolerate if I eat them at one week or two week intervals, but which will bother me if I eat them every fourth to fifth day. The ideal rotation interval can vary from patient to patient and from food to food, but should never be less than four days. On most patients rotation diets each food may be eaten more than once on the rotation day and the cycle is usually four to five days long.