Our study demonstrates that dietary modification is a frequently utilised self-management strategy employed by women with endometriosis in Australia, with gluten free, FODMAP and dairy free diets being the most popular amongst our respondents. Results suggest that dietary modifications are associated with perceived improvements in endometriosis-related symptoms, with women self-reporting an overall reduction in GI disturbance, nausea/ vomiting, fatigue, depression and sleep, however there did not appear to be one dietary strategy that was associated with greater perceived improvements. Through adopting various dietary strategies, over a third of respondents reported significant improvements in gastrointestinal disturbances such as abdominal discomfort, bloating, flatulence and diarrhoea. These are common symptoms of irritable bowel syndrome (IBS), a prevalent comorbidity of endometriosis, with women having a diagnosis of endometriosis being two to three times more likely to display IBS symptoms than those without a diagnosis.21, 22
There is some preliminary evidence that gluten-free diets can significantly reduce the severity of endometriosis pain in women, whilst also improving physical function resulting in improved quality of life.21 Gluten may have an impact on gut function via increased zonulin-mediated gut permeability that drives inflammation23 (in the presence of a weakened intestinal barrier), this stimulation of proinflammatory cytokines could go on to exacerbate endometriosis symptoms. Thus using a gluten-free diet to mediate IBS symptoms could in turn reduce the pelvic and gastro-intestinal symptoms of those with endometriosis. This is especially true for those with coeliac disease24 and with non-coeliac gluten sensitivity (NCGS).25, 26
The use of a FODMAP diet was also commonly reported. Common FODMAP fructans have been found to induce symptoms of IBS in those with NCGS27 and FODMAP foods28 are thought to increase gastrointestinal symptoms due to their indigestibility, which creates excess water and gas in the small bowel and proximal colon.28 A low FODMAP diet has previously been shown to be beneficial in reducing the symptoms of IBS in women with endometriosis in a cohort study.7 A low FODMAP diet has also been shown to show changes in inflammatory cytokines, microbiota profile and short chain fatty acids (SCFAs),29 which all have an impact on gut health in people with IBS. Another potential mechanism is that FODMAPs have been shown to cause visceral pain by increasing inflammation and bacterial endotoxins (such as lipopolysaccharides [LPS]) in the gut.30 This is interesting in light of the newly emerging “Bacterial Contamination Hypothesis” for endometriosis, which proposes bacterial endotoxins such as LPS may contribute to pelvic inflammation and the growth and progression of endometriosis itself.31
Whilst a low FODMAP diet may improve symptoms of endometriosis, it carries limitations as a long- term symptom management strategy. This diet was originally designed to be used over a restricted period of 2-6 weeks, depending on the severity of symptoms. Relaxation after this period is imperative as carbohydrate restriction may negatively impact gut microbiota, with a reduced number of overall luminal bifidobacterial found after four weeks of FODMAP restriction.32 This is likely due to the prebiotic effects of FODMAPs on gut bacteria that in turn may exert other benefits. A low FODMAP diets also risk altered nutrient intakes and potential deficiencies,33 with some evidence suggesting low FODMAP diets may alter the intake of fibre, calcium and B vitamins.34
A dairy-free diet may also be useful in reducing endometriosis-related gastrointestinal symptoms as lactose (a milk sugar) is a known FODMAP that may cause symptoms of IBS in those intolerant to it. Furthermore, A1 casein (a milk protein) found in cow-based dairy products may also promote gastrointestinal inflammation35 and IBS symptoms in those with self-reported lactose intolerance.36 This effect is likely mediated due to the pain inducing effects of histamine, an inflammatory compound released by mast cells upon the digestion of A1 casein-derived betacasomorphin-7 [BCM-7], a powerful histamine liberator.37 Histamine also stimulates ovarian oestrogen release, which may induce mast cell degranulation in the reproductive tissues.38 Oestrogen in turn stimulates mast cell histamine release,39 while also reducing the diamine oxidase (DAO) enzyme needed to break down excess histamine levels.40 As mast cells are highly localised around blood vessels and nerve fibers,41 they may play a role in the neuroinflammatory processes that underlie endometriosis pain pathophysiology.42 In one study, it was postulated mast cells could be targeted to minimise these recurring inflammatory processes underlying endometriosis.43 Mast cell activation is also associated with other endometriosis co-morbidities such as dyspareunia,44 dysfunctional uterine bleeding,45 an increased risk of pelvic pain46 and has an increased effect on women.39 As endometrial tissue and lesions are rich in mast cells, a diet free from A1 casein may therefore mitigate endometriosis pain by reducing mast cell activation and subsequent histamine release in endometrial tissues. It may be that restricting dairy confers some of the benefits of a full low FODMAP diet, however future studies are needed in women with endometriosis. It is plausible that these positive effects reported by those implementing these diets are likely mediated by the impact that removing or restricting these foods may have on inflammation and/or oestrogen metabolism. There is increasing evidence that visceral pain comorbidities (e.g. bowel or bladder conditions) can exacerbate chronic pain conditions and vice-versa47 and any reduction in GI disturbance may in turn reduce pelvic pain, via a reduction in intestinal distention and subsequent reduction in visceral nerve activation.7 Mental health improvement was also a noted outcome of dietary modification in the endometriosis cohort. Possible mechanisms of how this is achieved may extend to the well-established link between the gut/brain connection, inflammation and depression,48 with some research showing an association between pro-inflammatory diets and depression risk.49 It is thought brain inflammation results from a flood of inflammatory cytokines, a pathophysiological process also underpinning endometriosis-related inflammation. The improvements in mental health symptoms reported by our respondents may be explained in context of the impact that gut inflammation has on mood.50 Dairy-free diets in particular may help to alleviate symptoms of depression, as A1 casein (from dairy foods) in particular may exert a greater inflammatory, neurochemical impact on the body via its inflammatory opiate casomorphin (or BCM7)51. This has a cytokine stimulating, morphine-like influence that may drive mood and irritability disturbances, impact the immune system and hormonal function.52 Research also suggests a low FODMAP diet could relieve symptoms of depression,53 with one observational study linking low FODMAP diet to improved, long term symptoms of depression and increased levels of happiness.54
Despite the overall positive outcomes in symptoms reported by respondents adverse events were reported. Apart from gastrointestinal distress, which was relatively uncommon, other potential barriers to dietary modifications were reported including increased stress due to food restrictions, difficulty socialising, increased food preparation time and increased financial costs. Given the significant cost of illness burden already placed on women with endometriosis55 and the impact endometriosis already has on family and social relationships56 these may be significant barriers to long term dietary changes.