Diet plays a crucial role in the development and management of various skin disorders. While a vegan diet is sometimes viewed as a risk factor for skin diseases due to potential nutritional deficiencies, this perception may be overestimated. This article aims to debunk common myths and provide evidence-based information on the relationship between a vegan diet and inflammatory skin conditions, particularly psoriasis, while addressing potential nutritional deficiencies.
Introduction: The Role of Diet in Skin Health
The importance of diet in maintaining skin health cannot be overstated. Both inadequate and excessive nutrient consumption can be associated with skin disorders, including acne vulgaris, psoriasis, hidradenitis suppurativa, and atopic dermatitis. Diet is a significant contributor to the diversity of the gut microbiome, and an altered gut microbiome, or gut dysbiosis, is associated with an altered immune response, potentially promoting the development of such skin diseases.
Despite the acknowledged importance of nutrition, confusion persists regarding the ideal diet for optimal skin health, especially for individuals following a vegan diet. A vegan diet excludes all animal-derived products, including meat, poultry, seafood, eggs, dairy, gelatin, and honey, which may raise concerns about potential nutritional deficiencies and their impact on skin health. The vegan diet primarily consists of plant-based foods such as nuts, grains, seeds, legumes and their derivatives, fruits, and vegetables. However, ensuring sufficient intake of vitamins and nutrients through a well-planned vegan diet and appropriate supplementation can effectively prevent nutritional deficiencies.
While a recent review of nutritional deficiency and skin disease listed a vegan diet as a risk factor for riboflavin and vitamin A deficiencies, and a potential risk factor for lower protein intake, it's important to contextualize this information. This review will discuss nutritional deficiencies that can cause dermatologic manifestations, including clinical signs and prevention, for which a vegan diet is a potential risk factor. It will also examine the impact of a vegan diet on several common inflammatory skin diseases, with a focus on psoriasis.
Nutritional Deficiencies and the Vegan Diet
Riboflavin (B2)
Riboflavin, or vitamin B2, is a water-soluble vitamin essential for various reduction-oxidation reactions. Its active forms, flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN), act as electron carriers in the respiratory electron transfer chain, and FAD is necessary for the oxidation of fatty acids.
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Riboflavin deficiency classically presents with angular cheilitis and glossitis, occasionally with a confluent erythematous, scaly dermatitis of the scrotum or vulva and thighs, with sparing of the midline, as the initial cutaneous manifestation. During embryonic development, riboflavin deficiency can result in muscular, skeletal, and gastrointestinal abnormalities. Extracutaneous manifestations in adults include anemia, decreased iron absorption, neurodegeneration, and peripheral neuropathy.
Although some studies have indicated lower intakes of riboflavin in vegan diets compared to non-vegan diets, clinical riboflavin deficiency is not commonly reported in adults. A case study reported a male neonate presenting with life-threatening hypoglycemia and lactic acidosis due to maternal riboflavin deficiency, where the mother followed a strict vegan diet with occasional supplementation of vitamin B12, folic acid, vitamin D, and omega-3. This case underscores the importance of riboflavin intake for pregnant women on a vegan diet.
The recommended dietary allowance (RDA) for men and women over the age of 19 is 1.3 mg and 1.1 mg, respectively, with higher RDA levels for pregnant women. Plant-based foods that provide about 1 mg per serving of riboflavin include asparagus, bananas, beans, broccoli, figs, kale, lentils, peas, seeds, sesame tahini, sweet potatoes, tofu, tempeh, wheat germ, and enriched bread. Pregnant women on a vegan diet may need additional supplementation.
Vitamin A
Vitamin A is a fat-soluble isoprene derivative with several forms, including retinol, retinoic acid, and beta-carotene. It plays a vital role in the differentiation of epithelial tissues, protein synthesis in the eye, and modulation of the immune system. Overall, vitamin A deficiency is relatively rare. It can lead to abnormal epithelial keratinization, manifesting clinically as phrynoderma, generalized xerosis, and hair casts. Classic ophthalmologic manifestations usually co-exist with cutaneous disease and include xerophthalmia and night blindness.
One case report describes a child developing keratomalacia while on a strict vegan diet. He refused to eat most fruits, vegetables, and cooked meals, and his diet consisted only of non-fortified soy milk, potato chips, rice cereal, and juice. The authors suggest that a vegan diet puts children at risk for anemia, osteopenia, and protein and zinc deficiencies. However, this child’s extremely restrictive diet should not be generalized to all vegan diets. The Academy of Nutrition and Dietetics states that “appropriately planned vegetarian, including vegan, diets are healthful, nutritionally adequate, and may provide health benefits for the prevention and treatment of certain diseases”. They also state that vegan and vegetarian diets are appropriate for all stages of life, including pregnancy, lactation, infancy, childhood, adolescence, older adulthood, and for athletes.
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A well-balanced vegan diet contains ample vitamin A. Plant-based sources of vitamin A include leafy green vegetables, orange and yellow vegetables, tomatoes, red bell pepper, cantaloupe, and mango, as well as fortified breakfast cereals, breads, and juices.
Kwashiorkor
A common concern about veganism is protein deficiency. True protein deficiency leads to kwashiorkor, which should not be confused with marasmus, a form of nutritional deficiency caused by a lack of total calories. Kwashiorkor is exceedingly rare in developed countries such as the United States. It has rarely been described in developed countries, occurring in infants who were fed rice milk instead of breast milk or formula. Kwashiorkor can classically present with the cutaneous manifestation of “peeling enamel paint”, starting at sites of friction and progressively generalizing as the disease advances. Extracutaneous manifestations include gross edema and abdominal distention.
To prevent protein deficiency, the National Academy of Medicine recommends that adults consume a minimum of 0.8 g of protein per kilogram of body weight per day. A vegan diet can easily support the recommended daily protein intake as protein is found in nearly all plant foods, including legumes, nuts, seeds, and whole grains. A review article demonstrates that there is no evidence of protein deficiency among individuals on a plant-based diet in Western countries.
Traditionally, proteins were categorized as “complete,” meaning they contain all essential amino acids, or “incomplete,” meaning they lack one or more of the nine essential amino acids. Animal-derived foods (meat, poultry, fish, eggs, and dairy foods) tend to be good sources of complete protein, while individual plant-based foods (fruits, vegetables, grains, nuts, and seeds) often lack one or more essential amino acids. Those following a vegan diet who eat a variety of plant-based foods daily have no issue consuming all of the essential amino acids necessary for function. “Complete” plant proteins exist, and examples include quinoa and chia seeds.
Vegan Diet and Inflammatory Skin Disease
Acne Vulgaris
Acne vulgaris is an inflammatory skin disorder involving excess sebum production induced by androgenic hormones and insulin-like growth factor 1 (IGF-1) in hair follicles. Though the exact pathogenesis of acne triggers remains unclear, genetic, hormonal, lifestyle, and environmental factors have been shown to affect the development of acne. Historically, the relationship between diet and acne has been highly controversial.
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The consumption of dairy products such as cows’ milk has been correlated with acne. This may be explained by a positive association between increased milk consumption and IGF-1 concentrations. For adolescent boys, higher levels of skim milk consumption were associated with a higher prevalence of acne (p = 0.02), while for adolescent girls, significant associations were present with whole milk, low-fat milk, and skim milk (p < 0.005). Another study of female nurses also found a positive association between skim milk intake and acne (p < 0.005).
Foods with a high glycemic index (GI) have also been posited to worsen acne. In a randomized, controlled trial comparing a low- versus high-glycemic-load diet, after 12 weeks, the low-GI group had a statistically significant reduction in acne lesion counts compared with the high-GI group (p = 0.01). The low-GI group also had reduced weight, reduced free androgen levels (p = 0.04), and increased IGFBP-1 levels (p = 0.001). As an additional finding, an increase in the ratio of saturated to monounsaturated fatty acids of skin surface triglycerides was observed in the low-GI group, as well as an increase in follicular sebum outflow, which was associated with an increase in the proportion of monounsaturated fatty acids in sebum. Although the exact mechanisms by which the gut microbiome can influence the development of acne are unknown, a diet high in fat or foods with a high GI affects the intestinal microbiota by increasing intestinal permeability, which may aggravate the development of acne. Therefore, modulation of the gut microbiome or gut dysbiosis could potentially influence the appearance and evolution of acne. These findings suggest that GI, among other dietary components, may play a role in the pathogenesis of acne.
Other studies support the positive correlation between high-GI foods and acne. For example, a decrease in sebaceous gland size and sterol regulatory element-binding protein-1 expression in facial acne occurred after 10 weeks of a low glycemic load diet in 17 patients. The subjects in the low glycemic group also demonstrated significant clinical improvement in the number of acne lesions. In addition, a systematic review found that high GI and increased daily glycemic load intake were positively associated with acnegenesis and acne severity. Overall, the consumption of certain dairy products, such as cows’ milk, and foods with a high GI has a proacnegenic effect.
Dairy avoidance and a low-GI diet could be advantageous for patients with acne. Veganism, being a diet devoid of animal-based products and, when well-balanced, high in low-GI foods like fruits and vegetables, may promote anti-acnegenic effects. In fact, dietary intake of soy-based products appears to lower the incidence of acne. This effect may be attributable to the isoflavones and phytoestrogens in soy, which oppose androgen-induced sebum production. When 160 mg/day of soybean isoflavones was given to patients with acne for 12 weeks, there was a significant decrease in the number of acne lesions, likely due to decreased dihydrotestosterone levels. Soy protein may reduce visceral body fat, which could also improve acne. In general, the consumption of fruit and vegetables, which are foods with a low GI, may play a protective role due to their anti-inflammatory effect. Therefore, a well-balanced vegan diet may be beneficial in preventing and reducing acne lesions.
Psoriasis
Psoriasis is a Th1-driven chronic inflammatory skin disease with characteristic proinflammatory cytokines. Psoriasis is often comorbid with metabolic syndrome (MetS). MetS refers to the co-occurrence of several cardiovascular risk factors, including insulin resistance or type 2 diabetes, obesity, atherogenic dyslipidemia, and hypertension. The levels of proinflammatory cytokines are elevated in psoriasis, as well as in obesity and ischemic heart disease, and these cytokines have been shown to influence fat deposition, insulin action, and lipid metabolism. Thus, chronic inflammation may be the link between psoriasis and MetS, and the appropriate treatment of MetS could be crucial in the management of patients with psoriasis.
Diet is a relevant environmental factor in psoriasis since malnutrition, inadequate body weight, and metabolic disease may make the psoriasis more treatment-refractory. A cross-sectional study examining food intake patterns in psoriasis patients found two main dietary patterns. Pattern 1 was predominantly processed foods.
A 40-year-old female teacher presented to the rheumatology clinic in 2003 with nonspecific back, knees, and right ankle pain. She was subsequently diagnosed with psoriatic arthritis and was taking methotrexate to control her disease. Over the years, her symptoms were mostly under control. However, in 2018, after adopting a whole food plant-based diet free of added salt, oil, and sugar, she was able to stop taking methotrexate. She was discharged from the rheumatology clinic and has remained symptom-free since. The available literature on managing psoriatic arthritis with diet shows that less than 2% of patients with psoriatic arthritis are able to discontinue medication as a result of disease remission. A recent review of PsA treatment guidelines discusses pharmacological and nonpharmacological therapies, but at present little can be said about the impact of diet and lifestyle changes on PsA progression.
Encouraged by the positive change resulting from eliminating certain food products, she further adjusted her diet to eliminate all animal-derived foods, thus essentially adopting a vegan diet. This allowed for lowering the methotrexate dose to 12.5 mg per week. This was particularly important in her case considering a previous decrease in white cell count while on 20 mg methotrexate weekly. The patient was doing well on a dose of methotrexate ranging from 10 to 15 mg per week. Particularly interesting was the fact that she noticed significant worsening of the symptoms following the festive season over a few years.
Finally, in the second half of 2017, the patient decided to introduce even further dietary modifications and adopted a WFPBD. It involved no added salt, sugar, or oil; no refined (white flour, polished rice) or processed foods with added preservatives. She ate a variety of fruits, vegetables, beans, wholegrains, nuts, seeds, herbs, and spices. Normally, the patient had 3 meals per day with snacks of fruit in between. In September, the dose of methotrexate was lowered to 5 mg per week. Eventually, in February 2018, the patient stopped taking methotrexate and was discharged from the rheumatology clinic soon after as she did not experience any further symptoms associated with her arthritis. The patient has not been taking methotrexate or any other medications since February 2018, and her PsA has remained dormant.
An exclusively plant-based diet is an attractive option for patients with various forms of arthritis given its anti-inflammatory properties, a consequence of the vast quantities of antioxidant compounds and phytonutrients and their ability to lower markers of inflammation such as CRP. Our case adds further evidence for the potential of a WFPBD to support patients with PsA and the possibility to eliminate the need for medication.
The National Psoriasis Foundation states that over eight million people in the United States have psoriasis, an immune-mediated disease that causes inflammation. Dr. Klaper explains psoriasis and other skin conditions, such as eczema, can improve or even reverse with a whole-food, plant-based diet, and patients with psoriasis can change the inflammatory balance of their skin by changing the foods they eat.
Increasing evidence suggests a link between diet and psoriasis severity, with the latest findings suggesting benefit for diets rich in fruits and vegetables, whole grains, low-fat dairy foods and lean meats and low in salt and sugar. In short, diets like the DASH Diet and the Healthy Plant-based Diet seem to be associated with less severe psoriasis.
Researchers at King’s College London analyzed online survey data from 257 adults with psoriasis. Participants’ adherence to various diet quality scores, including the Mediterranean Diet Score, the Dietary Approaches to Stop Hypertension (DASH) score, and the Healthy Plant-based Diet Index, was assessed using a food frequency questionnaire. Psoriasis severity was self-assessed using a validated questionnaire. In addition to finding that individuals with very low adherence to the DASH diet index and the Healthy Plant-based Diet Index were significantly more likely to report higher psoriasis severity, the analysis showed that greater red and processed meat intake was associated with more severe psoriasis even when body mass index (BMI) was considered.
Fruits, nuts and legume intakes were also associated with less severe psoriasis, but this relationship was not independent of BMI.
A cohort study investigated dietary behaviors in patients with psoriasis in which a 61-question survey was applied to 1206 patients in the US. The results reported that 86% of all respondents made changes to their diet, noting that the best positive results on skin improvement were observed with the vegan, Pagano, and Paleolithic diets compared to the effects obtained with the gluten-free, Mediterranean, vegetarian, and carbohydrate-high protein diets. Dairy and sugar consumption was reported as one of the most common triggers for psoriasis, while meat and eggs were included as one of the minor common triggers.
Overweight and obesity are indisputable risk factors for the development of psoriasis and have been documented as factors for severe stages of the disease. The role of dietary interventions around psoriasis was investigated in a randomized controlled trial (N = 303) which reported the effects of a low-energy diet associated with physical exercise on the severity of psoriasis in patients with an elevated BMI that recently started treatment and whose response was not favorable with conventional systemic therapy with etanercept, infliximab, adalimumab, ciclosporin, and PUVA (8-MOP) psoralen combined with ultraviolet A therapy (8-methoxypsoralen). The results showed a decrease of 48% in the PASI (Psoriasis Area and Severity Index) score. It is well known that an increase in the adipose tissue in obesity tends to produce excessive amounts of proinflammatory cytokines which participate in the pathophysiology of psoriasis, including IL-8, IL-6, and TNF. Thus, if plant-based diets such as the vegan diet significantly decrease the BMI, and weight loss has a strong association with clinical improvement in psoriasis patients, it would be reasonable to suggest that these diets could be fundamental pillars for the management of psoriasis.
Regarding the studies mentioned above, a case study of a psoriatic arthritis patient has been reported, in which a whole-food plant-based diet was enough to achieve good disease response, such as decreased scalps, articular pain, stiffness, capsulitis, periods of articular discomfort, and uveitis.
In another case study, a 47-year-old male with a 28-year diagnosis of severe plaque psoriasis achieved remission of the disease after fast followed by adopting a plant-based diet.
With the above, it seems that the adoption of a plant-based diet that consists of limited or excluded animal-derived products and increasing the intake of vegetables, fruits, legumes, nuts, and cereal products is beneficial to skin health. As a result, this diet is low in saturated fat, trans fat, and arachidonic acid and high in antioxidants and omega-3 fatty acids, which together with its direct therapeutic effects of reducing inflammation and cutaneous symptoms and decreasing the risk of severe stages of the disease and indirect effects of promoting weight loss result in an improvement in the general life condition of these patients; therefore, using plant-based diets as a potential therapeutic option for the management of some psoriatic patients is recommended.
Atopic Dermatitis
Atopic dermatitis (AD) is the most common inflammatory skin disease, characterized by erythema papules and pruritic scaly plaques, predominant in skin folds such as hands, neck, and head. Worldwide, it has a prevalence of 2-3% in the adult population. Its etiology is multifactorial, being the result of the interaction of genetic and environmental factors and immunological activity. The pathogenesis of atopic dermatitis describes eosinophils and T-lymphocyte infiltration, apoptosis, changes in the skin microbiota, altered immune responses, and IgE (immunoglobulin-E) sensitization, leading to the deterioration of the skin’s stratum corneum and the epidermal barrier it constitutes.
The first relationship between diet and AD is their association with food allergies; thus, avoiding certain foods seems to be a good therapeutic base. However, a recent cross-sectional study found that there is no association between diet, specifically vegetarian and vegan diets, and the presence or severity of atopic dermatitis. However, class I obesity, a diet-related disease, was reported as a positively related factor with moderate to severe AD.
Past studies have shown the benefits of plant-based diets in the management of AD. In one open-trial study, a vegetarian diet significantly decreased the SCORAD (scoring atopic dermatitis, consisting of erythema, edema, crusts, and excoriation) index from 49.9 to 27.4 at the end of the intervention, with a similar effect of ciclosporin-A treatment.