The planning phase centers on identifying symptoms and potential problem foods. Professionally guided plans often eliminate a dramatic range of foods (sometimes even tap water) [source: WHC]. For the layperson, the most common approach is to eliminate the usual suspects -- dairy, soy, nuts, eggs, gluten, sugar and alcohol [source: Nassauer].
To individualize, some people keep a food journal for at least a week before starting, recording what they eat and how they feel throughout the day, which may suggest links, and noting which foods they eat most and crave most, since these often turn out to be culprits [source: UW Integrative Medicine].
Then, all those foods go away. The elimination phase typically lasts two to three weeks, which is enough time for symptoms to disappear if any of the eliminated foods were causing them. Some people experience withdrawal symptoms like fatigue or headaches in the initial few days [source: WHC].
During the elimination phase, it's important to keep a food diary (the dieter may have already been doing so) and to take in enough calories and eat nutritional substitutes for eliminated food groups [sources: WebMD, WHC]. For instance, if the diet calls for cutting out all dairy, other sources of calcium, like collard greens and figs, and vitamin D, like salmon and tuna, need to be added in [source: Mattheis].
By the end of the elimination phase, any food-related symptoms will have disappeared, and re-introduction begins. The goal is to learn exactly which foods are related to which symptoms, and detailed note-taking is crucial. The dieter adds foods back into the diet one at a time, with several days between each reintroduction to give the body time to reproduce any associated symptoms. If symptoms return after a reintroduction, that particular food (or food group) is likely causing them [source: FARE].
Once the dieter reintroduces all eliminated foods, the experiment is over, and it's time to formulate a long-term diet, preferably with expert help. Foods that appear to have triggered negative reactions may be eliminated for the long run, or they may be incorporated in doses determined not to trigger symptoms.
A long-term diet should be both free of triggers and nutritionally sound, and the latter may prove difficult if many nutritious foods or entire food groups were identified as triggers. This is one of the problems with DIY elimination dieting: When undertaken without expert guidance or oversight, they can end up causing harm.