The Gut and Psychology Syndrome (GAPS) diet, created in 2004 by Dr. Natasha Campbell-McBride, is promoted as a natural treatment for people with conditions that affect the brain, such as autism spectrum disorder. It is a controversial therapy that has received a lot of criticism for its restrictive regimen. The GAPS diet is an elimination diet that involves cutting out grains, pasteurized dairy, starchy vegetables and refined carbohydrates.
Understanding the GAPS Theory
Dr. Campbell-McBride theorized that a leaky gut causes several conditions that affect the brain, such as autism spectrum disorder (ASD). Leaky gut syndrome is a term sometimes used to describe an increase in the permeability of the gut wall, but it’s not recognised as an official medical diagnosis. The GAPS theory claims that a leaky gut allows chemicals and bacteria from your food and environment to enter your blood when they wouldn’t normally do so. Once they do, they can supposedly affect brain function and development, causing “brain fog” and conditions like ASD. The GAPS protocol is designed to help heal and seal the gut wall, prevent toxins from entering the bloodstream, and lower “toxicity” in the body.
However, it isn’t clear if or how leaky gut plays a role in the development of mental or neurological conditions, and the research on the effectiveness of the GAPS diet is limited. Despite Dr. Campbell-McBride’s claims, research on whether a leaky gut causes ASD is limited and mixed. ASD is a condition that results in changes to brain function that affect how the person experiences the world. Its effects can vary widely, but, in general, autistic people have difficulties with communication and social interaction. It’s a complex condition thought to result from a combination of genetic and environmental factors.
Some research suggests that up to 7 in 10 autistic people are likely to experience gastrointestinal symptoms like diarrhea, constipation, abdominal pain, acid reflux, and vomiting. This may lead to more severe behaviors, including increased irritability, aggressive behavior, social withdrawal, and hyperactivity. A 2020 review also found that some children with ASD may have increased intestinal permeability, but older studies have found no difference between intestinal permeability in children with and without ASD.
While some animal studies suggest a link, no studies have confirmed the presence of leaky gut before the development of ASD. So even if leaky gut is linked to ASD in some children, it’s not known if it’s a cause or a symptom. Overall, the claim that leaky gut is the cause of ASD is controversial. This explanation also oversimplifies the causes of a complex condition. More research is needed to understand the role of leaky gut and ASD.
Read also: Starting the GAPS Diet
The Two Phases of the GAPS Diet
The GAPS Diet occurs in two phases: the Introduction Diet and the Full GAPS Diet.
The Introduction Diet
The Introduction Diet is the first phase and lasts eighteen to thirty days, roughly three to five days per stage. It involves removing all foods that might be gut irritants, such as dairy, from your daily intake. You then reintroduce certain foods slowly and look for adverse reactions, such as stomach pain, hand flapping, seizures, or eczema. The very name Introduction Diet implies that we begin with this diet. It is helpful for most GAPS clients to go through the Intro Diet at some stage in their healing, because it gives them the best chance to optimize the healing process in the gut and the rest of the body. However, not everybody has to start from the Intro Diet and starting with the Full GAPS Diet. You may need a coach to navigate the Intro Diet or to choose which GAPS diet to start with.
The introduction phase is the most intense part of the diet because it eliminates the most foods. This is the most restrictive part of the diet. It is called the “gut healing phase” and can last from 3 weeks to 1 year, depending on your symptoms. In this phase, grains, pasteurized dairy, starchy vegetables and refined carbohydrates are eliminated, and broths, stews, and probiotic foods make up much of a person’s eating patterns. The GAPS diet recommends that you move from one phase to the next once you can tolerate the foods you have introduced.
If you’re already comfortable in the kitchen and currently eat a whole-foods diet, starting with the Introduction Diet may not be such an adjustment for you. However, if you tend to eat more processed foods, consider giving yourself a little time on Full GAPS first so that you can wean yourself off the sugar, salt, fillers, and stabilizers your body has come to crave. Once you begin to feel familiar and comfortable with the foods allowed during each stage of the GAPS Introduction Diet, you may feel more ready to launch into the Intro.
The Six Stages of the Introduction Diet
This phase is broken down into six stages:
Read also: Understanding the GAPS Diet
- Stage 1: Consume homemade bone broth, juices from probiotic foods and ginger, and drink mint or chamomile tea with honey between meals. People who are not dairy intolerant may eat unpasteurized, homemade yogurt or kefir. When you start Stage 1, bad bacteria begins to die off right away. It’s possible that this will make you feel physically sick (nausea, exhaustion, runs to the bathroom, and so on). This, too, shall pass! Stage 1 is based on three components: stock and soups made with meats, fish, and vegetables; probiotic foods; and fats.
- Stage 2: Add raw organic egg yolks, ghee, and stews made with vegetables, meat, or fish. Fresh herbs are not allowed until Stage 2. However, with a “bouquet garnish,” the herbs infuse the soup and are not actually ingested, so feel free to use them to add flavor to any soup. A bouquet garnish is a bundle of herbs tied together with cooking string, or wrapped in a bundle of cheesecloth and tied up with string. They are used to flavor soups, stocks, or stews. You can really put whichever herbs you desire in the bunch, but I most often tie together parsley, rosemary, thyme, bay leaf, and garlic. Fresh herbs are allowed in Stage 2 (and may be dried or fresh).
- Stage 3: All previous foods plus avocado, fermented vegetables, GAPS-recipe pancakes, and scrambled eggs made with ghee, duck fat, or goose fat.
- Stage 4: Add in grilled and roasted meats, cold-pressed olive oil, vegetable juice, and GAPS-recipe bread.
- Stage 5: Introduce cooked apple purée, raw vegetables starting with lettuce and peeled cucumber, fruit juice, and small amounts of raw fruit, but no citrus. Spices (which should be ground) are not allowed until Stage 5. Once you have reached Stage 5, be sure to add sea salt and fresh cracked pepper to all of the Intro recipes! Speaking of sea salt, buy unrefined sea salt with a tinge of color. If it is white-white, it means it has been refined and stripped of many of the beneficial trace minerals that you want!
- Stage 6: Finally, introduce more raw fruit, including citrus.
During the introduction phase, the diet requires you to introduce foods slowly, starting with small amounts. You may move on to the next phase once you can tolerate the foods you have introduced. You’re considered to be tolerating a food when you have a normal bowel movement.
The Full GAPS Diet
The Full GAPS Diet is the main portion of the diet and should last at least two years for maximum restoration of gut health. The full GAPS diet can last 1.5-2 years. It includes a wide selection of foods that can be prepared simply and are easy to digest. Soup, when properly prepared from nutrient-dense meat stock, provides an exceptionally easy-to-digest and nourishing meal that begins to heal the gut wall. The proteins in meat stock are partially broken down, giving your body a chance to rest while reaping the benefits of the stock’s healing power. Having these soups also removes most fiber from your diet, again allowing your digestive tract time to heal. Although you will have options for what kind of soup, just know that you will be eating what seems like dinner for breakfast and lunch for dinner. You will basically be throwing out all the food rules you are used to. On that note, always keep some soups on hand in the freezer in the event that cookin’ just ain’t gonna happen. I suggest making big batches of any three soups that are listed in this section, then simply alternating for the first several days. If you can prep them before of officially starting the diet, you’ll be psyched!
During this period, people are advised to base the majority of their diet on the following foods:
- Fresh meat, preferably hormone-free and grass-fed
- Animal fats, such as lard, tallow, lamb fat, duck fat, raw butter, and ghee
- Fish
- Shellfish
- Organic eggs
- Fermented foods, such as kefir, homemade yogurt, and sauerkraut
- Vegetables
Followers of the diet can also eat moderate amounts of nuts and GAPS-recipe baked goods made with nut flours.
There are also a number of additional recommendations that go along with the full GAPS diet. These include:
Read also: Comprehensive review of the GAPS Diet
- Do not eat meat and fruit together.
- Use organic foods whenever possible.
- Eat animal fats, coconut oil, or cold-pressed olive oil at every meal.
- Consume bone broth with every meal.
- Consume large amounts of fermented foods, if you can tolerate them.
- Avoid packaged and canned foods.
While on this phase of the diet, you should avoid all other foods, particularly refined carbs, preservatives, and artificial colorings.
The Reintroduction Phase
If you’re following the GAPS diet properly, you’ll be on the full diet for at least 1.5 to 2 years before you start reintroducing other foods. The GAPS diet suggests that the reintroduction phase may begin after you have experienced normal digestion and bowel movements for at least six months. Like the other stages of this diet, the final stage can also be a long process as you reintroduce foods slowly over a number of months.
The diet suggests introducing each food individually in a small amount. If you don’t note any digestive issues over 2 to 3 days, you may gradually increase your portions. The diet doesn’t detail the order of reintroduction or the exact foods you should reintroduce. However, it states that you should start with new potatoes and fermented, gluten-free grains. Even once you’re off the diet, you’re advised to continue limiting ultra-processed and refined high-sugar foods, retaining the whole-foods principles of the protocol.
Foods to Avoid
NO grains including wheat, rye, rice, oats, corn, maize, sorghum, barley, buckwheat, millet, spelt, triticale, bulgur, tapioca, quinoa, cous-cous, etc. The GAPS diet is an elimination diet that involves cutting out grains, pasteurized dairy, starchy vegetables and refined carbohydrates.
Considerations and Criticisms
As of 2025, very limited research has examined the effects of the GAPS dietary protocol on the symptoms and behaviors associated with ASD. Some studies suggest that it may help manage gastrointestinal symptoms, which can, in turn, prevent or reduce the severity of certain behaviors. Other studies performed by the International Society for Orthomolecular Medicine found that the GAPS diet had a positive effect on conditions like PANDAS, tic-related disorders, and various chronic diseases. However, studies have been small, and dropout rates are high, so it’s still unclear whether these diets may work and which people they may help. More research is needed to understand the role of the GAPS diet in managing neurodivergent conditions. Can dietary supplements help with ASD?
The effect of probiotics on the gut may be a more promising line of research. For instance, a 2019 study found that children with ASD had different gut microbiota compared to neurotypical children, and probiotic supplementation was beneficial. Other studies from 2017 and 2019 found similar results. The GAPS diet also suggests taking supplements of essential fats and digestive enzymes. A small 2021 study found that taking omega-3 fatty acid supplements had some positive effect on ASD behaviors. Older studies on the effects of digestive enzymes on ASD found similar results, but further research is needed.
The GAPS diet is a very restrictive protocol that requires you to cut out many nutritious foods for long periods of time. It also provides little guidance on how to ensure your diet contains all the nutrients you need. Because of this, the GAPS diet may increase the risk of malnutrition. This is especially true for children who are growing fast and need a lot of nutrients, since the diet is very restrictive. Additionally, those with ASD may already have a restrictive diet and may not readily accept new foods or changes to their diets. This could lead to extreme restriction.
Some people feel they’ve benefited from the GAPS diet, though these reports are anecdotal. The GAPS diet is extremely restrictive for long periods of time, making it difficult to stick to. Since this restrictiveness may lead to deficiencies in nutrition and growth, it may be especially dangerous for the exact population it’s intended for. The diet has not been scientifically tested, and the only claims in support of this diet are anecdotal. Some health professionals have criticized the GAPS diet because many of its claims are not supported by scientific studies.
It is true that there is emerging evidence to show that our gut health and brain are connected. However, that research has been mostly centered around conditions like anxiety and depression. It’s important to acknowledge how challenging dietary needs can become when you or someone close to you is diagnosed with a health condition. However, the GAPS diet is too restrictive and lacks scientific evidence to justify its implementation. Research examining the gut-brain connection is continually evolving.
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