A whole-food diet and obsessive-compulsive disorder: a pilot study

Upon entering the study, all participants will be randomly allocated into one of three baseline conditions - 1, 2 or 3 weeks. During these periods, participants will be eating their usual diets and will all be asked to have a blood test to measure for various markers of metabolic health, as well as vitamins and minerals. At the conclusion of the baseline period, all participants will then enter a one-week 'logistics week', in which they will receive materials which will outline all they need to know about the dietary intervention they are about to commence at the end of the logistics week, providing them time to prepare. Therefore, they will be required to go shopping for the necessary foods that will fit within the dietary interventions. There are two dietary interventions that will be used in this study; The Whole Diet, and The Whole Plus Diet. All participants will commence the first dietary intervention, The Whole Diet, for eight-weeks. At the end of this eight-weeks, if participants haven't experienced a clinically significant reduction in their OCD symptoms, they will continue to The Whole Plus Diet for a further eight-weeks. This will be determined by a clinician-rated outcome psychometric as well as the YBOCS score, which will be obtained from the 8-week check in at the end of the first dietary intervention. For those who do experience a clinically significant improvement in their OCD symptoms, they will conclude the trial after finishing The Whole Diet. The two dietary interventions are outlined below: The Whole Diet The Whole Diet is a whole-foods diet which centres on the removal of ultra-processed foods (UPF) from the diet. In this study, UPF will be defined using the NOVA classification system, which groups foods into four groups based on their level of industrial process (Carlos Augusto Monteiro, Levy, Claro, Castro, & Cannon, 2010). These four groups are unprocessed and minimally processed foods, processed culinary ingredients, processed foods, and ultra-processed foods (Monteiro et al., 2019). Ultra-processed food is defined as being industrial formulations which contain minimal to no whole food, such as chocolate, confectionary, ice-cream and soft drinks (Carlos A Monteiro et al., 2019). UPF are hyper-profitable, hyperpalatable (through the use of additives and flavours), have an extensive marketing budget, and are thus suggested to displace whole food consumption (Carlos A Monteiro et al., 2019). The Whole Plus Diet The Whole Plus Diet is a whole foods anti-inflammatory diet that removes common inflammatory foods including gluten and dairy (Asoudeh et al., 2023; De Punder & Pruimboom, 2013; Junker et al., 2012), as well as alcohol, caffeine, additives and refined sugar. This dietary pattern encourages unlimited consumption of whole foods (with an emphasis on diversity) of fruits, vegetables, meats, legumes, non-gluten containing grains, healthy fats, fermented foods, and herbs and spices. The Whole Plus Diet also allows ‘healthy treats’ including dark chocolate, honey and maple syrup. This diet is a modified Paleo diet (Cordain, 2002), and is based on the principles of the NOVA classification group one (whole, unprocessed foods) (Carlos Augusto Monteiro et al., 2010). It is also supported by research that has explored biological mechanisms that underpin the pathogenesis of OCD and other psychopathologies including inflammation (Gerentes, Pelissolo, Rajagopal, Tamouza, & Hamdani, 2019), metabolic health (Khalkhali, Rasekh, Eslamdoust-Siahestalkhi, Farrahi, & Zare, 2023) and gut dysbiosis (Turna et al., 2020) and foods that can promote these pathways. Research exploring OCD has indicated that the removal of gluten (Rodrigo et al., 2018) and foods high in free glutamate (Holton & Cotter, 2018) could be beneficial. Adherence to dietary intervention will be monitored by the participant being prompted 3-times weekly to send in a day of photos of their food, AI will be utilised to support us in determining the level of adherence. They will also complete two measures of self-efficacy for adherence to the diet.