The principle of a total exclusion diet is that you either fast, or eat just one or two specific foods, for a period of up to five days, then reintroduce and test foods. The fast or two-food period will clear your system of foods that you eat commonly, and should unmask background symptoms. You can become very weak and HI on a diet of this kind. You can do it at home, but should never do it without a doctor’s knowledge and supervision.
The best-known version of a two-food diet, the lamb and pear diet, is often prescribed for up to five days. You eat nothing but lamb (baked or grilled, with no oil or cooking fat) and pears, and drink nothing but water, preferably filtered or bottled. You can eat as much of these two foods as you want or need – for breakfast, lunch, tea or dinner – but nothing else at all.
Lamb and pears are chosen for the diet because, it is argued, they rarely cause reactions. The diet originated in the United States where lamb and pears are not common items in the diet, and hence are uncommon causes of allergy and intolerance. In the UK, however, they are much more frequently eaten and do cause reactions, although relatively rarely. Some doctors in the UK therefore prefer to use other, less often eaten foods, such as turkey and peaches, or rabbit and raspberry.
After the fast, or two-food diet, you start reintroducing and testing foods. Reintroduction is usually done on a stricter basis than for single-food testing or a special exclusion diet. It is usually recommended that you eat foods singly (not combined with any other foods), that you leave four hours or more in between testing foods, and that you organise foods on a rotation, so as to avoid problems with cross-reaction between related foods. (For more information on testing foods and organising a rotation diet. A doctor will usually give you a diet sheet to follow, based on your own history and preferences, which will help you with the complexity of planning. Depending on how many foods you test (and how many you react to), it can take between two and four weeks to devise a permanent diet.
The drawbacks of this type of exclusion diet are fairly obvious. It is time-consuming and almost impossible to combine with an active life. The foods you eat can be costly. You can be very weak and hungry while carrying it through, apart from any reactions you might get to foods you test. If you have a lot of food sensitivities, it can take a long time to devise a manageable diet.
On the other hand, if you are as highly sensitive as that, this is the only way to work out a tolerable diet, and it can turn up some surprises. People often find that they are not sensitive to foods that they had assumed to be a problem, and that, conversely, something unexpected turns up to be a real villain. Often just one or two foods turn out to be the root causes of symptoms and that can be an enormous relief. It really does sort out what is going on and if you can stick it out, it is an invaluable process.
There are two in-patient units in the UK where you can go through this type of diet with constant medical supervision.