Most people who end up at a metabolic psychology practice have already done a lot. Therapy. Medication. Lifestyle changes. They’ve been told their symptoms are stress, or habit, or something to manage rather than resolve. What they haven’t usually been asked is: how’s your gut? Not as a throwaway question — but as a serious clinical one. Because for a meaningful subset of people with depression, anxiety, brain fog, chronic fatigue or neurodevelopmental presentations, the digestive system is not a bystander. It is part of the problem. The GAPS nutritional protocol, Gut and Psychology Syndrome, starts from exactly this premise. It is a structured, staged dietary intervention designed to heal a disrupted gut lining, rebalance the microbiome and, by doing so, reduce the inflammatory and metabolic burden on the brain. It is not a quick fix and it is not for everyone. But for the right person, it can shift things that nothing else has. At Metabolic Psychology, Tiffany Baker is both a psychologist and an accredited GAPS practitioner, a combination that makes her well placed to work with clients for whom these two pieces of the puzzle belong together.

What is GAPS?

GAPS was developed by neurologist and nutritionist Dr Campbell-McBride. It builds upon the principles of the Specific Carbohydrate Diet (SCD). The central hypothesis is that intestinal dysbiosis, together with increased intestinal permeability, allows partially digested food particles and microbial metabolites to enter the systemic circulation, driving systemic inflammation that in turn affects neurological and psychiatic function.

The protocol aims to heal and seal the gut lining, restore a diverse and balanced gut microbiome, and reduce the total inflammatory and toxic burden on the nervous system. It is structured as a staged dietary intervention, beginning with an intensive Introduction Diet and progressing through a Full GAPS phase over an approximate period of 18 to 24 months, before gradual reintroduction of excluded foods.

The Science of the Gut-Brain Axis

The gut-brain axis refers to the bidirectional communication network linking the enteric nervous system, the autonomic nervous system, the hypothalamic-pituitary-adrenal axis, and the central nervous system. Gut microbiota play a significant role in this signalling: they produce neurotransmitters including serotonin and gamma-aminobutyric acid (GABA), modulate vagal afferent signalling, regulate immune activation and influence systemic inflammatory tone.

Research in inflammatory bowel disease (IBD) has demonstrated that gut dysbiosis is characterised by an increased abundance of pathogenic flora, a reduction in butyrate-producing species and an overall loss of microbiome biodiversity. Butyrate, a short-chain fatty acid, plays a significant role in intestinal homeostasis and the attenuation of mucosal inflammation. Dysbiosis and its downstream inflammatory consequences have been identified across a range of conditions relevant to mental health practice, including depression, anxiety and autism spectrum disorder.

It is worth noting that the scientific evidence base specific to GAPS as a clinical intervention is in its infancy. There are no large randomised controlled trials, and much of the published data consists of case series and observational reports. A 2024 paper published in the Journal of Orthomolecular Medicine examined eight case studies of individuals with inflammatory bowel disorders who undertook the GAPS protocol; all eight reported meaningful symptomatic improvement, including reductions in abdominal pain, diarrhoea and disease-related fatigue. These findings are preliminary but consistent with the biological plausibility of dietary modulation of the gut-brain axis.

What Does the GAPS Protocol Involve?

The protocol has two main phases. The Introduction Diet is the most intensive stage and involves a progression through six sequential stages, beginning with easily digested, nutrient-dense foods including homemade bone broth, boiled meats and well-cooked vegetables. Fermented foods, including 24-hour fermented yoghurt and lacto-fermented vegetables, are introduced progressively to support microbiome restoration. This phase may last from a few weeks to several months depending on the individual's response.

The Full GAPS Diet follows and is maintained for 18 to 24 months. It eliminates all grains, pasteurised dairy, refined carbohydrates, processed foods, starchy vegetables and legumes during initial phases. Permitted foods include meat, fish, eggs, non-starchy vegetables, nuts, seeds, most fruits, cold-pressed oils and homemade fermented dairy. The dietary framework is complemented by targeted supplementation, including probiotics, digestive enzymes and specific nutrients, which are individualised and introduced sequentially.

The protocol is demanding in terms of food preparation and dietary adherence. For this reason, psychological support alongside dietary coaching is an important component of successful implementation, particularly during the Introduction phase when detoxification reactions and dietary restriction can be distressing.

Who May Benefit?

The GAPS protocol was originally developed for children and adults with neurodevelopmental and psychiatric presentations where gut health was considered a contributing factor. Over time it has been applied across a broader range of conditions. It may be considered for individuals with depression and anxiety that is refractory to standard interventions, autism spectrum disorder, ADHD and other neurodevelopmental conditions, chronic gastrointestinal complaints including IBD, irritable bowel syndrome and food intolerances, Mast Cell Activation Syndrome (MCAS), autoimmune conditions and chronic fatigue, as well as presentations where there is a clear gut-symptom relationship or history of significant antibiotic use, formula feeding or early-life gut disruption.

It is important to note that GAPS is not appropriate for everyone. The protocol is quite restrictive and requires careful clinical assessment before commencement. It is contraindicated or requires significant modification in individuals with active eating disorders, severe nutritional deficiencies or certain medical conditions. Thorough individual assessment is always the starting point.

GAPS at Metabolic Psychology

Tiffany Baker brings a distinctive clinical skill set to our team. As both a psychologist and an accredited GAPS practitioner, she is well placed to support clients who are navigating the psychological dimensions of gut-brain dysfunction as well as the practical and emotional challenges of undertaking a therapeutic dietary protocol. Her areas of clinical focus include depression, anxiety and the psychological impact of chronic health conditions including MCAS, and she has experience working with children and families.

At Metabolic Psychology, GAPS sits within a broader multidisciplinary framework. Where appropriate, clients working with Tiffany on the GAPS protocol can also access input from our dietitians and our consultant psychiatrists. This integration of psychological support with dietary and medical expertise reflects our approach to metabolic mental health care: addressing the biological, psychological and lifestyle factors that together determine mental health outcomes.

You can read more about Tiffany here