Which diet for psoriasis?

There is no longer any doubt that being overweight is an important risk factor for psoriasis and psoriatic arthritis.

A recent study – with data from 753,421 individuals showed a strong, direct correlation between Body Mass Index (BMI) and the risk of psoriasis (ref 1). In fact, for a 1 unit increase in BMI, there was a 9% increase in risk for psoriasis.

At the same time, there is ample scientific evidence to suggest that a reducing diet – especially if you are overweight – is likely to lead to substantial improvements in the severity of your psoriasis and psoriatic arthritis (ref 2 & 3). This has been discussed in detail in a previous article called overweight and psoriasis.

But the question we are often asked is whether there is a specific reducing diet (e.g. Atkins, Paleo, South Beach, Alkaline Diet etc) which can be shown to be more effective than others for those with psoriasis and/or psoriatic arthritis?

Of course, there are literally hundreds of articles and websites on the internet which make claims about this, including many seemingly convincing personal stories. However, some of the claims are not only misleading, but clearly bogus and potentially harmful. The only way to adjudicate is by looking at the scientific evidence – and therein lies the problem.

So far as I am aware, there are no studies which have compared various diets in terms of their effect on psoriasis. The most recent and comprehensive review of its kind (Cochrane Review), which included all the relevant evidence, makes no mention whatever of specific diets in comparison with others (ref 4). This conspicuous lack of evidence represents an important knowledge gap which makes it difficult for doctors and patients to discuss this.

Nevertheless, two other recently published reports offer some interesting and helpful insights.

Reported dietary behaviours in patients with psoriasis

In the first study of its kind, the National Psoriasis Foundation (NPF) in the US carried out a questionnaire survey of the dietary habits, preferences and perceptions of 1206 patients with psoriasis and what effect these habits had on the severity of their skin disease (ref 5).

The researchers achieved a response rate of 60% which is good enough to allow some meaningful conclusions to be drawn. The average age of the sample was 50.4 years and 73% of the survey participants were female.

Here are some of the highlights from their findings:

• Compared to an age and sex-matched control group, psoriasis patients consumed significantly less sugar, wholegrain fibre, dairy and calcium, whilst consuming more fruits, vegetables and legumes
• 86% reported using dietary modification and the percentage reporting skin improvement was greatest after reducing alcohol (53.8%), gluten (53.4%), nightshades (52.1%)* and after adding fish oil/omega-3 (44.6%), vegetables (42.5%) and oral vitamin D (41%)
• Specific diets with the most patients reporting a favourable skin response were Pagano (72.2%), Vegan (70%), Paleolithic (68.9%), Gluten-free (52.9%), Low carbohydrate-high protein diet (51.7%), Mediterranean diet (48.4%) and Vegetarian diet (40.4%) 

*nightshade vegetables belong to the family of plants with the Latin name Solanaceae, examples of which are potatoes, tomatoes, peppers and eggplants.

It’s very important to note that these observations do not represent scientific evidence of efficacy. This is simply a report of what psoriasis patients do and is not a direct comparison of any of the diets.

There are, of course, many other diets such as the South Beach Diet, Ornish Diet, Dukan, Alkaline and Atkins Diet etc - including one or two absurdities like the Blood Group Diet. But as with those mentioned in the survey above, there is currently no scientific evidence to recommend any one of these specifically for patients with psoriasis.

The available evidence suggests that the key factor in dietary modification is reduced calorie intake and weight loss – and it is the weight loss which appears to have the beneficial effects on psoriatic skin lesions by reducing inflammation. Thus, to the extent that any diet produces weight loss, it will probably have a beneficial effect on psoriasis.

However, that is not quite the end of the story!

The Mediterranean Diet

A recent report shows that a Mediterranean Diet may be the best choice for patients with psoriasis (ref 6).

The NutriNet-Santé program is an ongoing, observational, web-based questionnaire cohort study launched in France in May 2009. The present study was performed within the framework of the NutriNet-Santé program, with data collected and analyzed between April 2017 and June 2017. Data on dietary intake (including alcohol) were gathered during the first 2 years of participation to calculate the MEDI-LITE score (ranging from 0 for no adherence to 18 for maximum adherence).

Patients with psoriasis were identified via a validated online self-completed questionnaire and then categorised by disease severity: severe psoriasis, non-severe psoriasis, and psoriasis-free. Of the 35,735 respondents, 3,557 (10%) individuals reported having psoriasis, which was severe in 878 (24.7%) of cases. The results were analysed to estimate the risk of having severe psoriasis or non-severe psoriasis compared with being psoriasis-free.

The results demonstrated that adhering to the main elements of the Mediterranean Diet was associated with a significantly lower risk of severe psoriasis. Accordingly, the authors suggest that the Mediterranean diet should be integrated into the routine management of patients with psoriasis.

Again, of course, this is not a comparison of the Mediterranean Diet with any of the other diets mentioned previously. Nor is it a properly conducted trial to establish efficacy (there is no control group included). It simply shows that the structure of the Mediterranean Diet may be helpful for patients with psoriasis. Remember too, that the Mediterranean Diet is a healthy choice for almost everyone, not just those with psoriasis or psoriatic arthritis.

Conclusions
What conclusions can we draw from the available evidence? I think there are four:

1 - No scientific study has yet compared the impact of specific diets – South Beach, Ornish, Palaeolithic, Atkins, etc – in terms of their impact on psoriasis

2 - It follows that – in terms of psoriasis – there is no basis on which to recommend one diet over another

3 - The key factor appears to be weight loss and it is this which reduces inflammation and leads to improvements in skin lesions

4 - A Mediterranean Diet has been shown to confer important health gains for the wider population, whilst also having a significant beneficial impact on psoriasis and arthritis.

So, whether you are overweight or not, we recommend the Mediterranean Diet as the most suitable dietary option. If you wish to lose weight, you simply reduce the total calorie intake so that you lose around 1-2lbs per week. If you already have a healthy body weight, you can still follow the Mediterranean Diet** for general health.

** We have covered the Mediterranean Diet previously in Psoriatic lifestyle and nutrition and you can view or download the full PDF version.

Author:
Dr David Ashton MD PhD
1 October 2019

 

Scientific References
1. Budu-Aggrey A,, Brumpton B, Tyrrell J, et al. Evidence of a causal relationship between body mass index and psoriasis: A mendelian randomization study. PLoS Med. 2019; 16(1): e1002739. Published online 2019 Jan 31.doi: 10.1371/journal.pmed.1002739

2. Debbaneh M, Millsop JW, Bhatia BK et al. Diet and Psoriasis: Part I. Impact of Weight Loss Interventions J Am Acad Dermatol. 2014; 71(1): 133–140.

3. Alotaibi HA. Effects of Weight Loss on Psoriasis: A Review of Clinical Trials
Cureus. 2018; 10(10): e3491. Published online 2018 Oct 24. doi: 10.7759/cureus.3491

4. Shu-Hua K, Ching-Chi C, Mei-Ling Y et al. Cochrane Database of Systematic Reviews Lifestyle changes for treating psoriasis. Cochrane Systematic Review - Intervention Version published: 16 July 2019. https://doi.org/10.1002/14651858.CD011972.pub2.

5. Alfi L, Danesh MJ, Lee KM et al. Dietary Behaviours in Psoriasis: Patient-Reported Outcomes from a U.S. National Survey Dermatol Ther (Heidelb) 2017; 7(2): 227–242.

6. Phan C, Touvier M, Kesse-Guyot E, et al. Association Between Mediterranean Anti-inflammatory Dietary Profile and Severity of Psoriasis: Results From the NutriNet-Santé Cohort JAMA Dermatol. 2018; 154(9): 1017–1024.