Clinical Review

Reexamining the Role of Diet in Dermatology

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Fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs) are short-chain carbohydrates that are poorly absorbed, osmotically active, and rapidly fermented by intestinal bacteria.44 The low FODMAP diet has been shown to be efficacious for treatment of irritable bowel syndrome, small intestinal bacterial overgrowth (SIBO), and some cases of inflammatory bowel disease (IBD).44-49 A low FODMAP diet may have potential implications for several dermatologic conditions.

Rosacea has been associated with various gastrointestinal tract disorders including irritable bowel syndrome, SIBO, and IBD.50-54 A single study found that patients with rosacea had a 13-fold increased risk for SIBO.55,56 Treatment of 40 patients with SIBO using rifaximin resulted in complete resolution of rosacea in all patients, with no relapse after a 3-year follow-up period.55 Psoriasis also has been associated with SIBO and IBD.57,58 One small study found that eradication of SIBO in psoriatic patients resulted in improved PASI scores and colorimetric values.59

Although the long-term health consequences of the low FODMAP diet are unknown, further research on such dietary interventions for inflammatory skin conditions is warranted given the mounting evidence of a gut-skin connection and the role of the intestinal microbiome in skin health.50,51

Gluten-Free Diet

Gluten is a protein found in a variety of grains. Although the role of gluten in the pathogenesis of celiac disease and dermatitis herpetiformis is indisputable, the deleterious effects of gluten outside of the context of these diseases remain controversial. There may be a compelling case for eliminating gluten in psoriasis patients with seropositivity for celiac disease. A recent systematic review found a 2.2-fold increased risk for celiac disease in psoriasis patients.60 Antigliadin antibody titers also were found to be positively correlated with psoriatic disease severity.61 In addition, one open-label study found a reduction in PASI scores in 73% of patients with antigliadin antibodies after 3 months on a gluten-free diet compared to those without antibodies; however, the study only included 22 patients.62 Several other small studies have yielded similar results63,64; however, antigliadin antibodies are neither the most sensitive nor specific markers of celiac disease, and additional testing should be completed in any patient who may carry this diagnosis. A survey study by the National Psoriasis Foundation found that the dietary change associated with the greatest skin improvement was removal of gluten and nightshade vegetables in approximately 50% of the 1200 psoriasis patients that responded.65 Case reports of various dermatologic conditions including sarcoidosis, vitiligo, alopecia areata, lichen planus, dermatomyositis, pyoderma gangrenosum, erythema nodosum, leukocytoclastic vasculitis, linear IgA bullous dermatosis, and aphthous ulcerations have reportedly improved with a gluten-free diet; however, this should not be used as primary therapy in patients without celiac disease.66-71 Because gluten-free diets can be expensive and challenging to follow, a formal assessment for celiac disease should be considered before recommendation of this dietary intervention.

Low Histamine Diet

Histamine is a biogenic amine produced by the decarboxylation of the amino acid histidine.72 It is found in several foods in varying amounts. Because bacteria can convert histidine into histamine, many fermented and aged foods such as kimchi, sauerkraut, cheese, and red wine contain high levels of histamine. Individuals who have decreased activity of diamine oxidase (DAO), an enzyme that degrades histamine, may be more susceptible to histamine intolerance.72 The symptoms of histamine intolerance are numerous and include gastrointestinal tract distress, rhinorrhea and nasal congestion, headache, urticaria, flushing, and pruritus. Histamine intolerance can mimic an IgE-mediated food allergy; however, allergy testing is negative in these patients. Unfortunately, there is no laboratory test for histamine intolerance; a double-blind, placebo-controlled food challenge is considered the gold-standard test.72

As it pertains to dermatology, a low histamine diet may play a role in the treatment of certain patients with atopic dermatitis and chronic spontaneous urticaria. One study reported that 17 of 54 (31.5%) atopic patients had higher basal levels of serum histamine compared to controls.73 Another study found that a histamine-free diet led to improvement in both histamine intolerance symptoms and atopic dermatitis disease severity (SCORing atopic dermatitis) in patients with low DAO activity.74 In chronic spontaneous urticaria, a recent systematic review found that in 223 patients placed on a low histamine diet for 3 to 4 weeks, 12% and 44% achieved complete and partial remission, respectively.75 Although treatment response based on a patient’s DAO activity level has not been correlated, a diet low in histamine may prove useful for patients with persistent atopic dermatitis and chronic spontaneous urticaria who have negative food allergy tests and report exacerbation of symptoms after ingestion of histamine-rich foods.76,77

Mediterranean Diet

The Mediterranean diet has been touted as one of the healthiest diets to date, and large randomized clinical trials have demonstrated its effectiveness in weight loss, improving insulin sensitivity, and reducing inflammatory cytokine profiles.78,79 A major criticism of the Mediterranean diet is that it has considerable ambiguity and lacks a precise definition due to the variability of what is consumed in different Mediterranean regions. Generally, the diet emphasizes high consumption of colorful fruits and vegetables, aromatic herbs and spices, olive oil, nuts, and seafood, as well as modest amounts of dairy, eggs, and red meat.80 The anti-inflammatory effects of this diet largely have been attributed to its abundance of polyphenols, carotenoids, monounsaturated fatty acids, and omega-3 polyunsaturated fatty acids (PUFAs).80,81 Examples of polyphenols include resveratrol in red grapes, quercetin in apples and red onions, and curcumin in turmeric, while examples of carotenoids include lycopene in tomatoes and zeaxanthin in dark leafy greens. Oleic acid is a monounsaturated fatty acid present in high concentrations in olive oil, while eicosapentaenoic acid and docosahexaenoic acid are omega-3 PUFAs predominantly found in fish.82

Unfortunately, rigorous clinical trials regarding the Mediterranean diet as it pertains to dermatology have not been undertaken. Numerous observational studies in patients with psoriasis have suggested that close adherence to the Mediterranean diet was associated with improvement in PASI scores.83-86 The National Psoriasis Foundation now recommends a trial of the Mediterranean diet in some patients with psoriasis, emphasizing increased dietary intake of olive oil, fish, and vegetables.87 Adherence to a Mediterranean diet also has been inversely correlated to the severity of acne vulgaris and hidradenitis suppurativa88,89; however, these studies failed to account for the multifactorial risk factors associated with these conditions. Mediterranean diets also may impart a chemopreventive effect, supported by a number of in vivo and in vitro studies demonstrating the inhibition and/or reversal of cutaneous DNA damage induced by UV radiation through supplementation with various phytonutrients and omega-3 PUFAs.81,90-92 Although small case-control studies have found a decreased risk of basal cell carcinoma in those who closely adhered to a Mediterranean diet, more rigorous clinical research is needed.93

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