Reintroducing foods after an elimination trial

The removal phase is the easy part. Anyone can eat beef for a fortnight. The reintroduction is where the information is, and it is the phase most people abandon, usually because they are bored rather than because it is hard.

Why bother

If you changed thirty things at once and feel better, you have learnt that the whole package works for you and nothing about which parts matter. That is enough if your only goal is to feel better and stay there. It is not enough if you want to know whether dairy is fine, whether onion is the problem, or whether you can eat in a restaurant without planning.

Reintroduction turns one observation into a set of rules you can carry.

The method

One food at a time. Five days between new foods. Nothing else changes during those five days.

Five days because most reactions that are going to show up will show up within three, and because it is short enough to keep going.

Log the same four things you logged during removal: stool form, pain, sleep, hunger. Add one line of free text about anything unusual, because the pattern often shows up in the notes before it shows up in the numbers.

If a food causes a clear reaction, stop it, wait until you are back to baseline, then test it once more before writing it off. A single bad day is often a coincidence, and the second test costs five days.

What order to add things in

Start with the foods you would most miss, unless there is a medical reason to test them last. Motivation is a resource and it should be spent on the thing that matters to you.

A workable order for most people:

Eggs first, because they are cheap, useful and rarely a problem outside a diagnosed allergy.

Hard cheese next. The lactose content is low, which makes it a cleaner test than milk.

Then butter and cream, which have more lactose than hard cheese and less than milk.

Then vegetables in ascending order of fermentable carbohydrate: courgette, spinach, lettuce, green beans, then carrots, then onion and garlic, then pulses, then stone fruit.

Wheat and other grains last, because they are the most complicated test and because if you are going to stop at some point, this is a decent place to stop.

What a reaction looks like

Bloating and wind within 24 hours. A change in stool form towards loose, or towards hard, that lasts more than a day. Pain returning to the level it was at before you started. Sleep disruption. A skin change.

What is not a reaction: feeling slightly fuller after a bigger meal, or one loose stool after a curry, or anything that happens once.

How much to eat when testing

A real portion, not a token one. Two eggs, a 30g piece of cheese, a quarter of an onion. A mouthful tells you nothing and a large portion can produce a reaction that a normal serving would not, which is a false positive you then live with for a year.

What to do with the result

Write down a list of what is in and what is out. That list is the actual output of the whole exercise.

Anything that is out can be retested in six months. The gut is not static and reactions change, sometimes because the gut changed and sometimes because the rest of the diet did.

When to stop testing and get help

If reintroducing a food produces vomiting, swelling of the lips or tongue, difficulty breathing, or a rash that spreads quickly, that is not a reintroduction reaction to manage at home. Stop, and get medical help.

If you cannot get back to baseline after two weeks off the suspect food, stop the experiment and speak to your GP.

If you find yourself becoming afraid of more and more foods, that pattern deserves attention in its own right. Restriction that keeps expanding is a known trap, and a dietitian is the right person to help with it. The British Dietetic Association has a directory of registered dietitians who work in this area.