AIP reintroduction: which foods to test, and in what order
Elimination only sets up the experiment. Reintroduction is where the answers come from.
Most of what is written about AIP is about the elimination phase, which is odd, because elimination on its own tells you almost nothing. Feeling better while avoiding twelve food groups doesn’t identify which of the twelve mattered. That answer only arrives when you put foods back one at a time and watch what happens — which makes reintroduction the phase that actually produces the thing you started for.
It is also the phase people rush, and a rushed reintroduction is worse than none: test two foods in the same week and a reaction tells you nothing about which one caused it. This is a general reference, not medical advice — worth going through with a clinician who knows your history.
When to start
Not on a date. The usual floor is 30 days of elimination and many people run 60 to 90, but the deciding factor is whether your baseline has settled enough that a change would be noticeable. Testing a food against a noisy baseline produces an unreadable result, and you will have spent a week to learn nothing.
Two practical conditions: your symptoms have been reasonably steady for a couple of weeks, and you have a daily record going back far enough to compare against. If you have not been logging, that is the thing to fix before testing anything — see how to start the AIP elimination diet.
How one test works
A single test is one food, introduced deliberately, then a watch window with nothing else changed:
- Pick one food. Not a meal containing it — the food itself, in as plain a form as you can manage.
- Eat a small amount, then more. A common approach is a small portion, wait, a larger portion later the same day if nothing happens, then stop.
- Watch for about seven days. Eat nothing else new during the window. Reactions are not always same-day, which is the whole reason the window is a week and not an evening.
- Call it. Safe, trigger, or unclear — recorded, so you are comparing notes rather than memories.
Seven days is the standard window and the one the app defaults to. Some people extend it for slower-moving symptoms; nobody usefully shortens it.
The four stages, in order
The order is not arbitrary. It runs from the foods least often reported as reactive to the ones most often reported, so that your early tests are the ones most likely to succeed — and by the time you reach the hard ones, you have practice reading your own results.
| Stage | Foods | Why here |
|---|---|---|
| Stage 1 | Egg yolks · Ghee · Fruit- and berry-based spices · Seed-based oils · Peas and green beans | The least commonly reactive group, so it goes first — an early win, and a gentle test of your own method before anything harder. |
| Stage 2 | Egg whites · Seeds · Nuts · Cocoa · Butter | Egg whites are separated from yolks deliberately: their proteins are reported to react more often, so testing them together would tell you nothing about which half caused it. |
| Stage 3 | Eggplant · Sweet peppers · Paprika · Coffee · Fermented dairy | The first nightshades, mildest first. Fermented dairy comes before other dairy because fermentation breaks down some of the proteins. |
| Stage 4 | Tomato · Potato · Chili peppers · Other dairy · White rice · Gluten-free grains · Alcohol | The most commonly reported reactives, saved for when you have a reliable baseline and some practice reading your own results. |
Finish a stage before moving to the next, and stay within a stage in whatever order suits your life — there is no requirement to test foods you don’t want back.
The foods most often flagged
Some foods carry a reputation in AIP guidance, and knowing which ones explains most of the ordering above. None of this predicts your result — plenty of people reintroduce nightshades without incident — but it does explain why these are tested late and separately.
| Food group | Why it’s flagged |
|---|---|
| Nightshades | The most commonly reported trigger family in AIP guidance — which is why they are spread across stages 3 and 4 rather than tested together. |
| Dairy proteins | Casein and whey are frequently reported reactives, and the reason dairy is split into fermented (stage 3) and everything else (stage 4). |
| Egg whites | Reported to react more often than yolks. Tested separately for that reason — yolks in stage 1, whites in stage 2. |
| Alcohol | Flagged less for a specific protein than for its effect on gut permeability, which is why it sits at the very end. |
| Coffee | Caffeine plus a documented cross-reactivity with gluten proteins in some people makes it a frequently flagged reintroduction. |
A food with no reputation is not a safe food — it is a food that gets singled out less often in the literature. Your own result is the only one that applies to you.
What makes a result readable
- One food at a time, always. The single rule that everything else serves. Two foods in one window is a wasted week.
- Don’t test through a bad week. Illness, travel, a deadline, poor sleep — anything that moves your symptoms on its own will be indistinguishable from a reaction.
- “Unclear” is a real answer. It means retest later, not guess now — forcing a verdict is how a food map fills up with entries you can’t trust.
- A trigger isn’t necessarily permanent. Plenty of people retest a food months later with a different result. Record what you found and move on rather than treating it as a life sentence.
- Write it down the same day. By week six nobody remembers what week two felt like, which is exactly the comparison a verdict depends on.
What doesn’t get reintroduced
Gluten and soy are not on the ladder. AIP treats them as out rather than as things to test on this schedule, so they never appear in a stage — the four stages above are the complete list of what gets tested.
What you end up with
Once the stages are done, the output isn’t a diet — it’s a list. Everything that came back clean is food you eat again, and the handful that didn’t is a short personal list to leave out or retest later. That list is the entire point of the protocol, and it is why the record-keeping during elimination matters more than the strictness.
Still in elimination? The elimination food list covers what to eat now, and how to batch cook for AIP covers making it sustainable long enough to get here.