You have probably tried more than one of them. Low FODMAP. Low oxalate. Low salicylate. Low histamine. Maybe paleo, maybe keto, maybe carnivore for a while, maybe a formal mast cell protocol handed to you by a practitioner. Each one helped, at least for a bit. Then something else turned up, or the old reactions crept back in despite you being more careful than you have ever been.

The list of diets you have tried keeps getting longer. The list of foods you can eat without thinking twice keeps getting shorter. If that gap feels familiar, you are not alone. I have been there too. Every one of these diets is really only managing one part of a much bigger system, including your gut microbiome, stress and the nervous system, genetics, your environment and your body's nutritional requirements.

There is a loneliness to this too that rarely gets talked about. Watching everyone else order off the menu without a second thought, missing dinners out or family celebrations because nothing on the table feels safe, having to explain, again, why you cannot just eat what is served. It is not only the food list that shrinks. Your social life can shrink right along with it, and that isolation is real, even when the people around you mean well.

I know this one from the inside as well as the clinic. At my worst, I was down to five foods and still reacting. For a while, even that was not enough, and I lived on a formula for a few months to try to settle my gut and nervous system. The formula actually made things worse. I understand exactly what it is like to miss out on eating like everybody else, and the isolation that restriction can cause. I know it is not all in your head.

What causes food intolerance and sensitivity?

Whichever diet you have landed on, FODMAP, oxalate, salicylate, histamine, keto, or carnivore, it changes more than the food on your plate. It changes what your gut bacteria get to eat, how reactive your mast cells are, and whether your body is getting the nutrients it needs to repair and regulate itself. When it comes to your gut bacteria, different bacteria run on different fuel, so cutting a category of food does not remove bacteria evenly. It changes which populations get fed and which ones go hungry, and your gut answers back with more of some kinds and fewer of others. Bacteria are also adaptable and resilient, so it is not actually possible to starve them out completely. Instead of trying to starve the "bad" bacteria, what we actually need to do is feed the good ones and get the gut moving properly.

Diet is only half of that equation. Your nervous system determines how well your gut can actually use what it is given, and how well your gut functions. During stress, your nervous system can slow down or speed up your digestive tract, think stage fright causing vomiting, or sudden nerves triggering diarrhoea. Your nervous system also controls gut motility, delivers the nutrients that feed the gut lining and mucus layer, and keeps that mucus layer intact so bacteria stay inside the gut instead of crossing into your bloodstream. That is also why stress can show up as constipation or diarrhoea. A nervous system stuck in fight, flight or freeze slows or speeds up digestion, thins that mucus layer, and loosens the gut lining, all of which changes the bacterial population you may be trying to manage with diet. Change the food without settling the nervous system, and you are only ever working half of the problem.

Tap through the diets below to see what I mean. This illustrated gut shows what can happen to your gut bacteria across different diets. You can see the population of beneficial bacteria drop, so they cannot do their job of feeding the gut lining and crowding out anything unhelpful. You can also see the increase in inflammatory bacteria, the ones that produce compounds like hydrogen sulphide, ammonia, trimethylamine, LPS and E. coli type organisms, changing depending on what is actually reaching them.

How does the gut lining get damaged?

A 2016 study from Stanford's Sonnenburg laboratory, published in Cell, found that a gut microbiota deprived of dietary fibre erodes the colonic mucus barrier that normally keeps bacteria at a safe distance from the gut wall, leaving that lining more exposed to whatever is nearby. (Desai et al., Cell, 2016.) Your gut lining is the first line of defence for your immune system, so when it is compromised like this, food sensitivities can follow. Several of the diets on this page, low FODMAP, keto and carnivore especially, remove a lot of that fibre. That does not make the diets wrong. It does mean the gut lining and the mucus layer protecting it need attention too, not just the food list.

Fibre loss is not the only thing that can set this off. A bout of gastroenteritis, food poisoning, or a course of antibiotics can each disrupt the gut lining and wipe out beneficial bacteria in one hit. That can be a real contributor to the original food sensitivities, and it is often why a restrictive diet gets introduced in the first place, whether that is IBS or another symptom flaring up afterwards. Either way, following a course of antibiotics or a gut bug with a low fibre diet does not help your gut microbiome recover from that assault.

Why trying another diet often makes food intolerance and sensitivity worse

When a diet stops working, the instinct is to remove more. Cut another food group, tighten the list further, try something more extreme. It makes sense. It is also, more often than not, the thing that keeps the cycle going.

A 2014 study in Nature showed that diet rapidly and measurably reshapes the human gut microbiome, and that a diet heavy in animal products and light in plant fibre moves the population toward bile tolerant organisms and away from the fibre fermenting bacteria that protect the gut lining. (David et al., Nature, 2014.) That change happens within days, which is part of why a diet that felt like relief at first can start producing new reactions only weeks later. The gut population underneath you has already changed.

None of these diets are the enemy here. Low FODMAP genuinely settles a flared gut, particularly if you have been diagnosed with SIBO. Low oxalate matters for some kidney stone histories. Keto and carnivore can calm inflammation in the short term, and a very short list of foods can be exactly the right call when the gut needs a break. However, when a restricted diet becomes long term, it becomes a much bigger issue.

That is why the work underneath the diet matters just as much as the diet itself. We settle the nervous system so the gut lining and mucus layer can heal, and motility improves. We rebuild the microbiome diversity the diet took out, so the gut has the resilience to cope with whatever you may encounter in the future.

A different approach to food intolerance and sensitivity: the 5R protocol

Inside the Happy Without Histamine Method, I use the 5R protocol, in this order: relieve, regulate, repair, restore and reintroduce. No matter what diet you arrive with, we work with where you are at to start healing the underlying causes of the symptoms, so you can get foods back in again. Where possible, we do not add any more restriction on top of the restricted diet you may already be on, whether that is FODMAP, oxalate or salicylate. We start with whichever diet is already in place.

Nervous system regulation, through brain retraining, somatic practices and MAP Rapid Rewire Coaching, addresses the chronic threat state that reduces gut function. Gut repair rebuilds the lining and restores the gut microbiome. Food reintroduction then happens in a deliberate, evidence based sequence, focused on gut microbiome restoration and building a resilient gut, so the diversity that protects against reactions comes back, instead of the diet shrinking further.

This is the same approach whether the diagnosis on your file says MCAS, histamine intolerance, IBS, SIBO, or nothing at all yet. The mechanism underneath is the same gut and nervous system relationship, whichever diet brought you here.

Who this is for

This work is most likely to resonate if you:

• Have tried two or more restrictive diets, low FODMAP, low oxalate, low salicylate, paleo, keto, carnivore, low histamine, with only partial or short lived relief
• Have been on a restricted diet for a long period of time, or multiple times in your life
• Suspect, or have been told you might have, MCAS, histamine intolerance, IBS or SIBO
• Notice your reactions move with stress, hormones or how well you slept, not just what you ate
• Have been through, or are currently on, a very restricted diet, down to a handful of foods, or a formula, just to feel safe eating
• Are ready to stop managing food and start understanding why your body is reacting in the first place

Frequently asked questions about food intolerance and sensitivity