Dieting and Food Allergies
Although some food allergies may eliminate "good" foods (such as nuts, shellfish, and a few others), it seems that the majority of restrictive diets simply eliminate "bad" foods. In addition, it is possible to substitute alternatives for the "good" foods that may be eliminated.
For instance, although my diet eliminates dairy, which contains calcium, a nutrient especially essential for women, I am able to take calcium supplements and substitute some soy alternatives (which are higher in protein) to make up for any calcium deficiency. My diet also forces me to eat foods which are higher in "good" fats (i.e. nuts, shellfish, lean meat) and to eliminate unhealthy sugars and chemicals.
As previously mentioned, an individual with food allergies is also forced to plan ahead; a skill which is essential to any dieter. When traveling or eating out, I have learned to pack healthy (healthy out of necessity, not only choice!) or "emergency" snack bags so that I am prepared.