Is the GAPS Diet backed by evidence?

The GAPS diet is short for Gut and Psychology Syndrome. It was created and trademarked by Natasha Campbell-McBride, MD, a neurosurgeon from the U.K. who obtained additional training in neurology and nutrition.

Campbell-McBride described the GAPS diet protocol in the book Gut and Psychology Syndrome: Natural Treatment for Autism, Dyspraxia, A.D.D., Dyslexia, A.D.H.D., Depression, Schizophrenia. First published in 2004, a second revised and expanded edition was released in 2010. Campbell-McBride described the GAPS protocol as a modified spinoff of the Specific Carbohydrate Diet (SCD).¹

Why was this diet developed?

Campbell-McBride created the food plan with the goal of curing her child of being autistic. She reported that it worked. This information has not been independently verified.

Has this diet been studied? What have researchers found?

No formal clinical trials have been conducted to study the GAPS diet, and there is no definitive scholarly evidence that it works.

GAPS has been mentioned in a handful of research articles, which are discussed in more detail in the Research Review further down in this article.

But scholarly articles are often behind paywalls, so without academic research access, it can be hard to read them.

Proponents of the GAPS protocol state that it has successfully cured autism for many families. An internet search about the GAPS diet produces hundreds of results, from health articles to parenting blogs. Some claim that the diet could be proven if research funding was available.

The reality? A formal clinical study is unlikely. Here’s why:

• The GAPS diet is highly restrictive, which means that review boards that approve clinical trials may not feel like the food plan is ethical, especially if it’s being studied in children.
• The program is lengthy, lasting up to two years. That’s a lot of time, commitment, and funding. While a shorter study could be done, if it shows no benefits, those who believe GAPS works would argue that the study wasn't long enough to show benefits. To accurately study the food plan, a clinical trial would need to be as long as the typically recommended GAPS plan.
• But a diet program that long would probably have a huge drop-out rate, so even if a study was designed, funded, and started, the end results would likely lead to inconclusive results from a lack of data.

Unfortunately, this means that the questions about the GAPS plan will remain.

What have wellness professionals said?

• Kelly Brogan, MD, a psychiatrist, mentioned the GAPS protocol in an academic journal article that was a perspective piece. The article stated that a GAPS diet was “indicated for patients with psychiatric and neurologic symptoms” although there were no citations to support that claim.²

• Katie Wells, known as the Wellness Mama, is an influencer and blogger. In a blog post, the GAPS diet was recommended to families with kids who are ADHD/autistic or have food allergies and eczema, among other things. While the endorsement likely influenced the decisions of many, the post was not written by a healthcare provider or nutrition researcher. No direct citations or evidence were provided to support the promotion of GAPS as effective for any reason, especially neurodivergence.³
• Will Cole, a chiropractor and functional medicine practitioner who also has a doctorate in natural medicine, called GAPS a “powerful gut-healing tool” in an article on his website. But the article also said that when asked about GAPS research, it’s limited. However, the post went on to make a common argument: Studies have considered how the gut interacts with certain conditions, and other research has shown that addressing the gut in those conditions can help, and so, since the GAPS diet is designed to address gut issues, it can be applied for this reason, too.⁴

What do critics say about the diet?

• There are concerns about the diet’s highly restrictive food plan, which could lead to nutrient shortfalls.
• People with sensory sensitivities may find it unpalatable.
• Those who have food allergies may find it inaccessible, since many of the foods on the plan are common allergens (like eggs, peanuts, tree nuts, and fish).
• Autism, ADHD, and neurodivergence in general aren't diseases. As such, they can't be "cured" with diets or supplements. Claims that GAPS or other diets can do this are not supported by evidence.

The US News Best Diets rankings pops up in search results a lot. While their process for ranking diets isn’t academic, they do consult nutrition and diet experts. Their article about GAPS noted that it is tedious, monotonous, and loaded with rules that can be hard to remember. The last item in their pro/con list is the most important one: There's little research to back it up.⁵

What is the diet like?

Part Two of the GAPS diet book details the food plan. People who follow the GAPS protocol initially need to avoid:

• All grains and anything that contains them
• All starchy vegetables, some beans, and legumes (like potatoes, sweet potatoes, cassava, arrowroot, peas, soybeans, and chickpeas)
• All lactose and foods that contain it (including all dairy except lactose-free, casein-free homemade kefir, yogurt, and sour cream)
• All sugar and any products that contain sugar (though it allows raw honey and dried fruit)
• All processed foods, including commercially available oils (like vegetable oil, margarine, canola oil, etc.)

Foods included on the GAPS plan:

• Unprocessed red meats, game meats, poultry, organ meats, and seafood
• Bone broth
• Eggs (including raw egg yolks)
• Non-starchy vegetables (like beets, asparagus, broccoli, Brussels sprouts, cabbage, cauliflower, eggplant, kale, onions, mushrooms, bell peppers, pumpkin, and tomatoes)
• Nuts, seeds, and flours made from them (recommended as replacements for grains and include walnuts, almonds, cashews, sunflower seeds, pumpkin seeds, and others)
• Some beans, lentils, and legumes (like navy beans, lima beans, string beans, peanuts, and split peas)
• Ripe fruits (for example, bananas must have brown spots to be considered ripe enough), but not at the same meals with meat
• Animal-origin fats (like lard, duck fat, and ghee) and virgin, cold-pressed olive oil

The GAPS plan involves several phases and includes a complex reintroduction process for some foods that are excluded in the first part of the protocol.

From a food safety standpoint, the GAPS plan recommends raw egg yolks and raw milk, which are red flags. The book says that when purchased from the right source, raw milk comes “without any risk of infections,” but this is not verifiable or accurate. The book is not aligned with basic food safety protocols implemented to prevent food-borne illness.

Are there disability-related concerns or accessibility issues with the diet?

Yes.

Mobility

The book states that all foods should be bought fresh and prepared at home. For people with chronic conditions, neurodegenerative disorders, and other physical mobility limitations, this isn’t feasible. Even if they have a partner/caregiver, the amount of burden that would be added to that person’s load is intense with this food plan.

Fatigue

While fatigue can be a generic symptom of many conditions or diseases, it’s ubiquitous for many who might consider diet or wellness approaches to help. While some dietary changes may improve fatigue over time, other requirements from food plans can worsen fatigue or drain energy. For people with ME/CFS, Long Covid, multiple sclerosis, and other disorders with severe fatigue, it’s sometimes impossible to go to a kitchen to get a plate of already-prepared food, let alone to cook everything needed from scratch after buying it fresh on a weekly basis. Fatigue realities have to be considered as valid, serious accessibility concerns.

Financial

There are significant cost concerns when comparing the expense of a typical diet with the GAPS diet. While Katie the Wellness Mama has written that the diet doesn’t noticeably increase costs, her baseline food approach differs dramatically from households experiencing food insecurity or poverty. Food plans that are gluten and grain-free tend to be more costly, especially if you previously had no dietary restrictions. When these are medically indicated from food allergies, they still cause financial strain. Adopting a restrictive, expensive food plan with no definitive proof can further compound a vulnerable financial or food insecure situation.

Food access

The GAPS program suggests a lot of foods that aren’t typical for grocery shelves across the country. If someone lives in a food desert or has limited access to markets (or transportation to get there), the ability to get all the foods needed to follow a GAPS plan is further reduced. A concern is that someone would follow the plan with whatever they can access, afford, or find. But since the GAPS diet is already restricted, further reductions due to accessibility (or even allergy-related) issues could introduce greater risk for nutrient shortfalls and malnutrition.

Digestive function

Many chronic conditions come with digestive side effects. While the GAPS plan claims that it can address gastrointestinal issues, there’s also plenty of potential for the protocol to worsen or cause new ones. Major dietary overhauls can trigger setbacks for people with chronic or autoimmune conditions. The book notes this, but refers to it as a type of die-off reaction. That doesn’t mean that it’s advisable from a nutrition expert’s position. Digestive distress, even from supposedly positive changes, can worsen aspects of digestion, absorption, or other conditions. Before making dietary changes, it’s important to speak with a registered dietitian to consider pros and cons.

Healthcare access

Sometimes, special diets are tried in place of medical care. This can happen if a person doesn't have access to healthcare providers due to lack of insurance coverage or they’ve tried and felt like doctors and other providers failed, ignored, or gaslit them.

Trying new diets and protocols is common among people with chronic illness or disability, and it’s rarely discussed with doctors first. Many times, it’s because medical providers downplay how much dietary changes might help because, if they practice from an evidence-based position, they have to consider what is known. Regarding a GAPS diet, for example, it wouldn’t be possible for a provider to say that it could help, because no evidence shows that. A doctor can’t say for sure that it won’t help, but for ethical reasons, it’s not good patient care to suggest that something entirely unproven is safe or maybe helpful. This is why patients often make their own decisions about dietary changes, and leave their doctors out of the conversation.

Individuals have every right to choose how they nourish their bodies. Intuition can’t be entirely discounted. However, if you are changing your diet to deal with new symptoms or extensive issues, make sure that you’ve talked to medical providers first. Many wellness and diet protocols are aimed at curing or reversing conditions that have never objectively been proven to be cured, and their patient’s success stories or product reviews aren’t verifiable evidence or proof.

Conflicts of interest

Conflicts of interest are not definite red flags. However, they need to be considered when evaluating an overall program, protocol, or provider. It’s hard to be perfectly objective about a product or program that is providing financial benefits to a person or company.

The GAPS plan exists in a book, which retails for between $14-$24. Getting exact stats on book sales is impossible, however, Amazon lists it as a top bestseller in several categories:⁶

• Top 15 in Autism Spectrum Disorder
• Top 15 in Abdominal Disorders & Diseases
• Top 20 in Diet Therapy
• Top 30 in Medical Nutrition
• Top 35 in Abdominal Disorders & Diseases (Kindle list)
• No. 155 in Other Diet Books

These rankings change every hour, but the GAPS book consistently ranks in the top 100 for many of these categories.

People can also pay to become GAPS certified so that they can sell their GAPS consultation services to clients (which, like most alternative or functional nutrition services, are probably out of pocket expenses).⁷

• For $2,450, doctors and providers with formal health or nutrition education can pay to become GAPS-certified practitioners.
• For $2,450, people with no nutrition education but who have followed the GAPS diet for at least several months can pay to become GAPS-certified coaches.
• Neither certificate is accredited or approved by higher education boards.

Research Review

This review isn’t an exhaustive. It will be updated as new data becomes available.

Last updated: September 2024

Case Study (2020)

A paper detailing the results of a case study that involved one teenager diagnosed with PANDAS was published in the Journal of Orthomolecular Medicine.⁸

• The protocol lasted for 18 months.
• The study authors claimed that the teenager’s condition was reversed.

It’s important to know that case studies cannot tell researchers whether something works on a larger scale. They might be used to design future studies, but one person is one person. There are too many variables that could lead to positive effects. It’s great when something is helpful for a person, but from an evidence-based standpoint, we cannot take one person’s success story to justify the effectiveness of a diet or program.

The article also didn't thoroughly discuss limitations, which leave a lot of big question marks. These are just a few:

Limitation 1: The authors credit GAPS for reversing gut-related health issues. But the diet is grain-free, gluten-free, mostly dairy-free, and eliminates countless other foods. It isn't possible to prove that the GAPS diet specifically was responsible for the benefit. It could have been the removal of one component only, or due to non-diet-related factors. There's no way of knowing. This case study can't serve as scientific proof that the GAPS diet works for PANDAS or other gut-related conditions.

Limitation 2: The article was retrospective. This means that the protocol was used months or maybe even years before the actual data was looked at. At the time of publication, the case study teenager was described as thriving in college, so it seems likely that a few years had passed. People often struggle to remember things exactly as they were, which is a big downside of this type of study.

Limitation 3: Many other factors in the participant's life could have helped or led to improvements, not just the GAPS diet (or any food intake). Since it’s a one-person case study conducted based on past experience, there’s no way to know for sure. The study authors could have strengthened their evidence by including more of these details, but since we don't have them, we have to consider that many things could have affected the reported outcome.

Limitation 4: One of the article’s authors is Campbell-McBride, the creator of the GAPS dietary protocol. Two other authors are GAPS-certified. It’s not wrong to study a diet a person created or paid to be certified in. However, it introduces a potential conflict of interest and uncertainty about the level of researcher bias or objectivity, which may have influenced how the study was written or how the authors reached their conclusions.

Pilot Study (2019)

The results of a study meant to test the concept of a GAPS diet for autism were published in the Proceedings of the Latvian Academy of Sciences.⁹

The 3-month study involved 17 children (10 who were autistic and 7 who were not) and the researchers concluded that GAPS was “a safe and effective approach for reducing some symptoms” in autistic kids.

This is not the same conclusion I reached after reading the study, more of which I’ll discuss below. This is why it’s important to read beyond the abstract.

This study wasn't designed in a way that could lead to cause-and-effect conclusions about the GAPS diet or the outcome. The study also had major limitations. Here are just some of them:

• The study was not blinded or randomized. This increases the risk of bias for the research team and the participants. This also reduces the level of certainty about any conclusions or outcomes.
• The intervention included both a diet and supplements. Any possible benefits could have come from the food, supplements, both, or neither (like a placebo effect). There were too many confounding factors to conclude any direct or indirect associations between the diet and the reported outcome.
• The diet group in the study only followed it with 40-80% compliance and parents self-reported that information based on their estimation. If anything, the parents were probably more likely to report greater compliance, not less, than actually occurred. Regardless, if a person only followed a diet 40% of the time but also took supplements, it’s not possible to say with any certainty that the diet itself can be given credit for benefits.
• The control group’s diet was their usual diet but the study doesn’t report or describe what that might have been. If two groups are compared, and one is a control, it's important to have a baseline understanding of what a "usual" diet means in this context. Usual could mean only fast food, only homemade food, only gluten free food, only ethnicity-specific food, too much food, or too little food due to food insecurity. Without adequate information about that control group, it’s impossible to compare them to the diet group.
• Both groups had significant improvements in their gastrointestinal symptoms. It’s great that most kids noticed benefits, but if the diet group and the non-diet group did, the treatment diet probably didn't help with GI symptoms.
• On a questionnaire that measured social behaviors, the diet group had greater improvements than the non-diet group. These results were reported by parents who completed questionnaires, not by asking the kids. These social improvements could have been influenced by parent perception. Research involving autistic kids, in particular, is prone to high levels of placebo effects. Here's how:
  • Did the parents, who knew their child was on a special diet to “help,” create more positive social situations?
  • Were they themselves less stressed because of their perceived hope from the diet?
  • Did lower parental stress levels help the kids feel more socially relaxed?
  • The possibilities are extensive, but true objective analysis isn’t possible here.
• The study’s results were collected from parent observations of children, not from the kids following the diet themselves. As mentioned, the placebo effect heavily influences this kind of collected information. When parents know that their child is on a diet with a goal to “fix” or “improve” some aspect of health or behavior, they tend to feel more optimistic and may less critically complete questionnaires relating to their child’s perceived habits and challenges.
• Questionnaires, even when they have been validated for scientific research, are highly subjective. But they’re especially subjective when someone (a parent) completes them based on what they see in someone else (their child).
  • In this study, one of the questionnaires showed 43% improvements in the GAPS group and only 14% in the non-diet group. But this particular questionnaire measured parental impressions of autistic behavior. “Autistic behavior” isn’t objectively measurable, and an optimistic parent is likely to consider this less bothersome than a parent who feels there’s no “hope” for their social situation. This type of survey is very prone to the rosy coloring of a placebo effect.
• The people following the diet weren’t consulted for their direct feedback.
  • Yes, they were kids, but the age range for the study was 2-18. Adolescents and teenagers are very capable of expressing, even if nonverbal, how foods and other things make them feel.
  • The appearance of improvements or certain symptoms based on parent or outside observations does not always translate to actual personal quality of life improvements.
  • Autistic people, in particular, are known to mask behaviors if they feel vulnerable. Major dietary changes can feel extremely unsafe, which could have led to perceived social improvements because the child felt scared, confused, punished, shutdown, or depressed.
  • None of these are actual observations, but as a researcher who objectively fact-checks and reviews studies, I have to ask about the many viewpoints and possibilities that could explain what the final outcome is said to be. Things are rarely what they appear to be, especially when study results are completed by observers or when autistic people are not allowed to be experts on themselves.
• In this study, families were given a choice to put their child in the diet group or the control group. This further elevates the risk for evidence that is biased in favor of the diet’s benefits, particularly on subjective behavior assessments.

Survey Comparison (2020)

The results of a survey-based study compared responses of 247 families with autistic kids to 267 families without autistic kids. The results were published in the International Journal of Environmental Research and Public Health.¹⁰

• This study didn’t specifically look to assess the effectiveness or performance of the GAPS diet or other food plans.
• Of the autistic part of the survey group, 15.4% followed GAPS, although the study noted that for the 3-month study period, some participants switched from one diet to another (and did not clarify which ones).
• This study noted that GAPS has been “very scarcely studied” and that effectiveness and safety about the diet are unknown.

Other Studies

Two other journal articles that mentions GAPS are reviews, both from 2019.^11,12 But review articles don’t provide new evidence, so these can’t be used as proof that a diet (or anything else) works.

Conclusion: There are major gaps in the evidence for the GAPS diet.

References

1. First edition from Medinform Publishing, Cambridge UK & Second edition by Chelsea Green Publishing www.chelseagreen.com/product/gut-and-psychology-syndrome/
2. https://www.liebertpub.com/doi/abs/10.1089/act.2015.21204?journalCode=act
3. wellnessmama.com/reviews/gut-psychology-syndrome-review/
4. drwillcole.com/gut-health/what-is-the-gaps-protocol-everything-you-need-to-know-about-this-powerful-gut-healing-tool
5. health.usnews.com/best-diet/gaps-diet
6. https://www.amazon.com/Psychology-Syndrome-D-D-D-H-D-Schizophrenia-ebook/dp/B07L1V8TTQ/ref
7. gapstraining.com/
8. https://www.researchgate.net/profile/Sophie-Delaunay-Vagliasindi/publication/362469018_GAPS_Nutritional_Protocol_as_a_Treatment_for_PANDAS_-_A_Case_Study/
9. https://www.researchgate.net/publication/357041272_Specific_Carbohydrate_Diet_SCDGAPS_and_Dietary_Supplements_for_Children_with_Autistic_Spectrum_Disorder
10. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7503400/
11. https://pubmed.ncbi.nlm.nih.gov/28762296/
12. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6495415/