Rajani Katta, MD1 and Mary Jo Kramer, BSc2
1Baylor College of Medicine, Houston, TX, USA
2Georgetown University School of Medicine, Washington, DC, USA

Conflicts of Interest:
Rajani Katta reports no relevant conflicts of interest. Mary Jo Kramer reports no relevant conflicts of interest.

ABSTRACT
An increasing body of research indicates that dietary change may serve as a component of therapy for certain skin conditions. This includes conditions such as acne, atopic dermatitis, aging skin, psoriasis, and rosacea. Certain nutrients, foods, or dietary patterns may act as disease “triggers”, while others may prove beneficial. Avoidance or elimination diets may be helpful in some conditions, although testing may be recommended first. In terms of beneficial effects, an eating pattern that emphasizes the consumption of whole foods over highly processed foods may help in the treatment of certain skin conditions, and will certainly help in the prevention of associated co-morbidities.

Key Words:
diet, elimination diet, skin, whole foods

Introduction

Dietary change has long been considered an important treatment strategy for certain skin conditions. For example, dermatologists have long discussed the role of dietary triggers in rosacea and insulin resistance in acanthosis nigricans. As an increasing body of research has demonstrated, dietary change may play a role in treatment strategies for other skin diseases as well.

In this review, we focus on five major skin conditions for which dietary change may be advised as one component of treatment. As a quick Internet search will reveal, there is much misinformation on the link between skin and diet. Some recommendations are ineffective, while others are potentially harmful, such as untested dietary supplements or severely restrictive elimination diets. It is critical, therefore, that physicians be well-informed in this area in order to provide evidence-based recommendations.

In this article, we review information on specific nutrients, foods, or dietary patterns that may act as disease “triggers”, as well as those that may prove beneficial in therapy. This review provides a synopsis, highlighting promising research findings.

Diet and Acne

Triggers

The strongest evidence to date on dietary triggers for acne is for high-glycemic-load diets. In a randomized controlled trial (RCT), acne patients demonstrated significant improvement after 12 weeks of a low-glycemic-load diet.1 Later studies documented that this dietary pattern resulted in lower androgen bioavailability and altered skin sebum production.2,3 In another RCT, a 10-week low-glycemic-load diet improved acne, and histopathological exam revealed decreased skin inflammation and reduced sebaceous gland size.4

Some studies have demonstrated an epidemiologically weak association between acne and dairy consumption, possibly more so with skim milk.5-7 While further research is needed, it may play a role in some patients, as in a report of five teenagers who developed treatment-resistant acne after starting whey protein supplements.8

Beneficial Measures

Studies in humans are limited and, therefore, despite promising in vitro, animal, or anecdotal reports, recommendations for foods or supplements containing probiotics, omega-3 fatty acids, zinc, antioxidants, fiber, and vitamin A cannot be made with certainty at this time.9 Omega-3 fatty acids warrant further study; in one 10-week RCT, omega-3 fatty acid supplements and gammalinolenic acid supplements both resulted in clinical and histopathological improvement in acne lesions.10 Probiotics warrant further study as well; in one RT, minocycline with probiotic supplementation resulted in a lower total lesion count as compared to antibiotics alone.11

Zinc bears special mention, as it has been studied in several RCTs. While some trials have not been successful, others have demonstrated efficacy in acne treatment.12,13 Further research is warranted, as published trials have utilized multiple dosages and forms of zinc, including zinc gluconate, zinc sulphate, and methionine-bound zinc, among others. Some formulations have better absorption and result in less gastrointestinal side effects. Other factors that impact zinc absorption include age and meal components.14 In addition, some successful trials have utilized zinc in combination with other components, such as antioxidants and lactoferrin.15,16 Future research must account for these multiple factors.

Diet and Aging Skin

Triggers

For patients who present for cosmetic treatment of aging skin, lifestyle factors that impact this process are an important aspect of treatment. While smoking and sun protection are commonly reviewed, dietary factors should be as well.

While it has long been recognized that diabetics experience poor wound healing, there is now a greater recognition that these effects on collagen can promote skin wrinkling. Higher levels of blood sugar can result in the production of advanced glycation end products (known as AGEs) via glycation and cross-linking of collagen fibers, which ultimately results in a loss of elasticity.17 Consumption of pre-formed AGEs, created during certain cooking processes such as deep-frying, can also be detrimental.18

Even in non-diabetics, effects on collagen may be seen. Even after accounting for degree of sun damage and smoking, as study subjects’ blood glucose level increased, their perceived age increased.19

Beneficial Measures

Many laboratory and animal studies have found that multiple different antioxidants (AOs), found in foods ranging from various fruits and vegetables to tea leaves and seeds, act to limit the damaging cutaneous effects of ultraviolet (UV) radiation.20 Experimental human studies of a few AOs have noted the same, as in one study in which subjects consuming tomato paste daily for 12 weeks experienced less UV-induced erythema, as well as lower levels of UV-induced matrix metalloproteinase.21 It is important to note that research indicates AOs consumed via dietary sources appear to function in a different fashion than those found in isolated supplements.22

Other human studies suggest that a diet high in phytonutrients can limit photodamage. One study reported higher intake of vegetables, legumes, and olive oil appeared to protect against actinic damage.23 In another study of over 4000 women, patients’ skin was analyzed for features of skin aging. After controlling for other factors, a diet reported as high in potassium and vitamins A and C correlated to fewer wrinkles.24

Diet and Atopic Dermatitis

Triggers

Food allergies are highly correlated with atopic dermatitis (AD). In some cases, they are causative.25 Foods may trigger an AD flare via three main mechanisms.26

Immunoglobulin E (IgE)-mediated allergy, also known as Type 1 or immediate-type hypersensitivity, may trigger a flare within minutes to hours.27 The six common trigger foods are milk, eggs, wheat, soy, seafood, and nuts. Testing with skin prick test or blood test may screen for this allergy, but due to a high rate of false positive results, confirmation requires double-blind, placebo-controlled food challenge (DBPCFC).

Late eczematous reactions, due to the same trigger foods, may cause an AD flare up to 48 hours later.28 As the immunological mechanism is unknown, testing requires DBPCFC.

Systemic contact dermatitis, screened for by patch testing, is a T-cell mediated reaction. In balsam of Peru allergy, some persons allergic to fragrance additives may experience a cutaneous flare following ingestion of certain foods, including tomatoes, citrus, and cinnamon.29

An expert panel, representing 34 agencies and groups, published guidelines on food allergy, and concluded that elimination diets are not recommended in unselected AD patients.30 In other words, dietary changes should be guided by results of testing. If suspected by history, though, a single food elimination diet for 6 weeks may be attempted in adults.

Beneficial Measures

Synbiotics, which are probiotics in combination with prebiotics, have shown promise in the treatment of AD. Probiotics are live bacteria, similar to those found naturally in the human body, and which may be beneficial to health. They may be found in supplements or in certain foods containing live, active cultures.31 Prebiotics, such as certain plant fiber, are defined as nondigestible carbohydrates that stimulate the growth of probiotic bacteria in the intestine.32 A meta-analysis of synbiotics in AD treatment found the most promise with a combination of different strains of bacteria and when used for at least 8 weeks in adults and children over the age of 1 year.33 However, the optimal dose, bacterial strains, and treatment duration remains unclear.

Vitamin D has not been shown to be helpful in most AD patients, but further research is recommended for certain groups, specifically those with very low levels of vitamin D, those with food allergies, and those with frequent bacterial skin infections.34,35 Studies of evening primrose oil and borage seed oil have been disappointing, while studies of Chinese herbal medicine have either not shown efficacy, or have been of low quality.36,37 Limited research is available for fish oil supplements.38

Diet and Psoriasis

The importance of diet should be emphasized to all psoriasis patients, primarily due to the higher risk of comorbid conditions, including diabetes, hypertension, and cardiovascular disease, that may be prevented or ameliorated by dietary approaches.39 In addition, dietary change leading to weight loss has resulted in better treatment efficacy, as well as improved psoriasis area and severity index (PASI) scores in some patients.

Triggers

It is well recognized that smoking and increased alcohol intake are associated with psoriasis, and all psoriatic patients should be advised of their potential role.40,41

Dietary factors may also play a role. Gluten-containing foods may act as a trigger in some patients, and testing for celiac antibodies is warranted in those who report gastrointestinal symptoms. While estimates vary, one large study found a 2.2 fold higher risk of celiac disease as compared to matched controls, while a meta-analysis found a 2.4 fold higher risk of certain celiac antibodies.42,43 In such patients, a gluten-free diet may result in psoriasis improvement, as demonstrated in small trials and case reports, although further studies are required to confirm.43,44

Beneficial Measures

In a systematic literature review, increased severity of psoriasis appeared to correlate with a higher body mass index (BMI), although the authors noted the difficulty in determination of temporality due to study designs.45 It is believed that obesity likely predisposes to psoriasis, and vice versa.46 While the reasons for this are multifactorial, it has been shown that weight loss can improve response to systemic psoriasis therapies and improve disease severity.

An excellent review article summarizes the effects of weight loss interventions in psoriasis.47 In a meta-analysis of five RCTs of lifestyle intervention via diet or exercise in overweight or obese psoriasis patients, a greater reduction in PASI score was seen in weight loss intervention groups.48 In a limited number of case reports and retrospective studies, some obese patients have experienced significant improvements in psoriasis following gastric bypass surgery.49

Weight loss has also improved response to systemic therapy, as in one RT trial of patients on cyclosporine.50 In examining factors associated with response to biologic therapy, one analysis found that BMI had the strongest effect across studies, although several studies found no association.47, 51

While specific dietary recommendations are not clear, one observational study found an inverse association between PASI score and degree of adherence to the Mediterranean diet.52

In terms of nutritional supplements, Millsop et al. summarized multiple studies and found that further investigation was needed, with fish oil showing the most promise and oral vitamin D demonstrating some promise in open label studies. There was limited evidence for benefit of vitamin B12 and selenium
supplementation.53

Diet and Rosacea

Triggers

Although dermatologists frequently counsel rosacea patients on avoidance of dietary triggers, there is a lack of research in this area. In one survey of patients by the National Rosacea Society, 78% had altered their diet, and 95% of this group reported subsequent reduction in flares.54

In this group, 75% were affected by spices and 54% by hot sauce. Other trigger foods included tomatoes (30%), chocolate (23%), and citrus (22%). Alcohol was another frequent trigger, including wine (52%) and hard liquor (42%), as well as hot beverages such as coffee (33%) and tea (30%).

While the underlying pathophysiologic mechanism of these reported triggers is unknown, transient receptor potential (TRP) channels may play a role. These are expressed throughout the body, including on neuronal tissues, and may be activated by cold or hot temperatures, as well as certain foods.55 Specific dietary activators include capsaicin and cinnamaldehyde, which act on certain of these channels to stimulate an increase in skin blood flow via neurogenic vasodilatation.55 Capsaicin is found in some spices, while cinnamaldehyde is found in cinnamon, tomatoes, citrus, and chocolate.56

Beneficial Measures

Research indicates the possible role of a gut-skin connection in rosacea. In a population-based cohort study of close to 50,000 patients with rosacea, the prevalence of celiac disease, Crohn’s disease, ulcerative colitis, Helicobacter pylori infection, small intestinal bacterial overgrowth (SIBO), and irritable bowel syndrome were all higher among patients with rosacea as compared with control subjects.57

Although research is ongoing, the pathogenic link remains unknown. One intriguing study found that patients with rosacea were 13 times more likely to have SIBO, with a suspected role for increasing circulating cytokines.58 Treatment of SIBO with antibiotics in 40 patients led to remission of rosacea in all cases, which persisted in the majority at 3-year follow-up.

In one case report, a reduction of gut transit time via a high-fiber intervention resulted in improvement of rosacea.59 As SIBO has been linked to decreased gut motility, further research on such intervention is warranted.

Conclusion

This article is intended as a general overview. There are several other conditions (not touched upon here) for which dietary intervention may be considered. For example, emerging research indicates that patients with hidradenitis suppurativa have a higher risk of adverse cardiovascular events, which may necessitate dietary change.60 In the arena of prevention, research continues into the role of diet and supplement use in skin cancer prevention. As research continues, dietary interventions may play a role in other dermatologic diseases as well.

The five conditions reviewed here are very disparate, and yet patients with each often seek dietary advice. In discussing the link between skin and diet, it is important to recognize and convey the limitations of nutritional research. Specifically, such research may not lead to definitive answers applicable to every patient, but rather general recommendations.

This is in part due to the notable variability of individual responses to different foods and nutrients, as in marked differences in blood glucose responses to the same quantity of carbohydrates.61 Confounding factors present a notable research challenge, as does the fact that many health effects may take months to years to manifest, which makes valid controlled dietary trials extremely challenging. Despite these challenges, nutritional research can indicate directions for further study, or add to an increasing body of evidence to support specific recommendations.

Based on research findings to date, certain dietary recommendations are suitable for patients with multiple different types of skin disease.

  1. The results of research support the promotion of eating patterns over specific foods or nutrients.
  2. An eating pattern that emphasizes the consumption of whole foods over highly processed foods may help in the treatment of certain skin diseases. It will certainly help in the prevention of associated comorbidities.
  3. Multiple eating plans emphasize whole foods as a foundational approach, and may be recommended to patients with skin disease. Such eating plans, rich in dietary antioxidants, fiber, and other phytonutrients, have demonstrated multiple overall health benefits. These may be either cuisine-based, such as the Mediterranean diet, or guideline-based, such as the DASH diet. These particular plans have been shown to reduce the risks of cardiovascular disease and hypertension, respectively.62,63
  4. An increased intake of fiber is seen as one key benefit of these whole foods diets. Some plant-derived fiber serves as a prebiotic, which may promote a healthy gut microbiome. Given an increasing body of research demonstrating a gut-skin connection, this may benefit certain inflammatory skin diseases.
  5. For some skin diseases, specific dietary “triggers” should be reviewed. Some patients may choose a trial of an elimination diet, such as avoidance of high-glycemic-load foods in acne or vasodilating foods in rosacea. For other conditions, medical testing may be recommended prior to dietary change, as in testing for celiac disease in psoriasis.
  6. Dietary supplements, used in the absence of a documented nutrient deficiency, have been demonstrated as beneficial in only a few very specific instances. Despite the marketing of many over-the-counter supplements for the treatment of skin disease, the vast majority of these are not supported by evidence.
  7. Referral to integrative physicians, dieticians, or nutritionists may be recommended to help implement and tailor dietary approaches according to food allergies, personal or cultural preferences, and other medical conditions.

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