Is psoriasis severity linked to consumption of ultra-processed foods?

Biscuits, ready meals, dairy desserts... Ultra-processed foods have invaded our daily lives. According to INSERM, in 2024, they accounted for nearly one third of our daily calorie intake. However, despite their convenience and taste, their nutritional profile is poor and raises concerns about health effects. Multiple studies have highlighted a link between a diet high in ultra-processed foods and increased risk of chronic diseases. Obesity, type 2 diabetes, cardiovascular diseases and even certain cancers are associated with these nutrient-poor foods high in refined sugars and saturated fats, which act as pro-inflammatory compounds. A recent study by dermatologist Émilie SBIDIAN and her team suggests that ultra-processed foods may play a role in the psoriasis.

To reach this finding, researchers examined profiles of more than 18,528 individuals aged 15 and over registered in the NutriNet-Santé database between 2021 and 2022. Among them, 1,825 had psoriasis and 803 presented an active form of the condition. Participants reported their daily intake of ultra-processed foods in milligrams (mg), though these values were not disclosed in the study. Researchers adjusted their analysis for several risk factors, including age, alcohol consumption, body mass index (BMI), and the presence of other conditions. Three groups were defined based on ultra-processed food consumption: low, moderate, and high. A correlation was found between the presence of psoriasis and a diet high in ultra-processed foods.

Individuals with active psoriasis were 36% more likely to be among the highest consumers of ultra-processed foods compared with those without psoriasis.

While the study does not demonstrate a direct causal link, only a correlation, it opens interesting avenues. The results appear to indicate that the association between the psoriasis and ultra-processed food consumption extends beyond the impact of that dermatosis on type 2 diabetes and cardiovascular disease. They suggest that additives and processing methods play a potential role in worsening inflammation. Several studies have shown an association between ultra-processed food intake and elevated levels of high-sensitivity C-reactive protein (hs-CRP) and tumour necrosis factor alpha (TNF-α), markers of inflammation.

One hypothesis concerns the high carbohydrate content of ultra-processed foods. After ingestion, these carbohydrates trigger an insulin peak, a hormone that promotes pro-inflammatory processes. Insulin stimulates interleukin-6 (IL-6) production, a pro-inflammatory cytokine, and may activate the insulin-like growth factor (IGF-1) pathway, involved in keratinocyte proliferation. However, the psoriasis being a chronic inflammatory condition characterised by excessive keratinocyte proliferation and immune system activation, this process may contribute to a vicious circle. A carbohydrate-rich diet may sustain a persistent inflammatory state that worsens psoriasis flare-ups.

It is important to note that the study has several limitations, as acknowledged by the researchers themselves. First, psoriasis cases were self-reported, which may cause misclassification. The cross-sectional design does not allow causal inference: it is impossible to determine whether the high intake of ultra-processed foods precedes or follows flares of psoriasis. Another limitation is the lack of detail regarding high or low ultra-processed food intake, which hinders interpretation of the results.

To elucidate the role of ultra-processed foods in the development of psoriasis, large-scale prospective studies remain necessary.

Although there is no single Mediterranean diet—each country has its own culinary practices—the cuisine has distinctive traits and is characterised by the predominant role of plant-based foods, such as fruits, vegetables, legumes, nuts, or seeds. Most health professionals agree the Mediterranean diet benefits the body and can support cognitive function, promote cardiovascular health, and regulate blood glucose. It may also offer a protective effect in cases of psoriasis.

A study of 257 adults with psoriasis who completed an online survey showed an inverse correlation between adherence to a diet rich in fruit and vegetables and the severity of psoriasis. In addition to answering questions about their diet, participants rated lesion severity using a scoring system that considered the appearance of psoriasis, the symptoms experienced and its psychological impact. Scientists then applied statistical adjustments to account for volunteers’ demographic characteristics, including age, sex, smoking status, height, weight, current treatment and any associated comorbidities.

Primary findings of the study indicate that people with low adherence to a Mediterranean diet are more likely to report more severe psoriasis.

These results require qualification. The study relies on self-reported data for dietary habits and psoriasis severity. This method may introduce bias linked to subjective symptom perception or imperfect dietary recall. It does not involve long-term follow-up but uses a cross-sectional survey, making it difficult to establish a causal link between the Mediterranean diet and psoriasis symptoms. Large-scale controlled clinical trials conducted over an extended period are needed to confirm or refute these observations.

How can these results be explained?

Several hypotheses may explain the Mediterranean diet’s potential protective effect on psoriasis severity. One relies on its anti-inflammatory action of its foods. Fruit, vegetables, and oils in this dietary pattern are rich in polyphenols. These compounds modulate inflammation by reducing IL-6 and CRP release. Moreover, unsaturated fatty acids from oily fish and olive oil play a key role in regulating immune responses. Studies show omega-3s can inhibit keratinocyte activation and limit immune cell infiltration in the skin, two processes involved in psoriatic plaque formation.

However, it is important to note that these effects were observed in studies in vitro where the concentrations of omega-3 used exceeded those achievable through a typical diet, even from omega-3-rich foods such as oily fish or plant oils. Moreover, omega-3s in these foods occur alongside other nutrients, such as antioxidants, proteins and other fatty acids, which can modulate their bioavailability and biological effects. It is difficult to conclude that omega-3 intake via diet will produce the same effects as those observed in vitro. The key remains to maintain homeostasis in the body by following a balanced diet rich in diverse nutrients and promoting a healthy lifestyle, including regular physical activity, which also helps modulate inflammation and support overall health.

To confirm that dietary advice can play a role in the management of psoriasis, the next step is to conduct a controlled clinical trial.