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Weight Loss Surgery and Psoriasis


It is well recognized that obesity is a risk factor for the development of psoriasis and psoriatic arthritis, and precedes the onset of these conditions in many cases.  There is also evidence to show that being overweight reduces the therapeutic benefit of many of the medications used in psoriasis.  In other words, if you are overweight you are more likely to get psoriasis and the medications used in treatment, will be less effective.  

Exactly why there should be such a strong association between psoriasis and obesity is not entirely clear, but both can be regarded as fundamentally inflammatory conditions.  Evidence shows that fat cells produce molecules called adipokines and cytokines which drive the underlying inflammatory response and thus make psoriasis and arthritis worse.  It follows that the impact of weight loss on psoriasis is of great interest to both doctors and patients alike.  Several studies suggest that weight loss can improve the symptoms of psoriasis, probably resulting from improved drug distribution and a reduction in circulating levels of inflammatory molecules (adipokines and cytokines).    

Over the past two decades, there has been a rapid increase in the numbers of obese patients undergoing a surgical weight loss procedure (bariatric surgery).  There is impressive scientific evidence to show that bariatric surgery delivers substantive, durable weight loss with major improvements in associated diseases such as diabetes, hypertension and abnormal blood fats.  In fact a surgical weight loss procedure has been shown to be the only really effective treatment for chronic obesity.  Moreover, those undergoing a surgical weight loss procedure, have a substantially lower risk of premature death and disability when compared with their non-surgical, obese counterparts.  So an intriguing question is what impact bariatric surgery has on psoriasis?  

At the 2015 Annual Meeting of the American College of Rheumatology, researchers from New York University presented some interesting results on a group of 86 patients with psoriasis who were included in a larger group of more than 9,000 individuals undergoing weight loss surgery.  The patients with psoriasis were asked to rate on a scale of zero to 10 the degree of improvement they saw in their psoriasis (or psoriatic arthritis) following surgery.

More than half of patients with psoriasis and 62% of patients with psoriatic arthritis reported that their disease improved.  Importantly, patients who had more severe psoriatic disease to begin with experienced more improvement, according to the data.  The improvement in arthritic symptoms is almost certainly attributable to reduced weight placing much less stress on inflamed joints.  

The problem with this study is that it was retrospective.  Asking patients to try and remember what their psoriasis was like before surgery is clearly unreliable because it introduces what is referred to as “recall bias”.   Researchers are now engaged in a prospective study in which patients with psoriasis are identified prior to surgery.  This will allow a more reliable comparison to be made between pre- and post-operative symptoms.  Nevertheless, other studies among obese psoriatic patients have shown that weight loss induced by bariatric surgery may decrease the severity of psoriasis, or eliminate it altogether, in anywhere between 40-60% of patients.  In some individual cases, the improvements may be dramatic.  For example, in two patients who underwent gastric bypass surgery, one patient’s body surface area (BSA) involvement went from 25 to 9 percent in six months, and the other patient’s BSA involvement went from 75 to <5 percent over the course of six years.  These studies have led some to suggest that bariatric surgery – especially the gastric bypass – may be a viable treatment option for patients with severe psoriasis.  

However, around one-third of psoriatic patients do not experience any skin or joint improvement after bariatric surgery and some (around 10-12%) may actually experience a worsening of their symptoms.  Why should this be the case?  

Scientists believe a possible explanation for surgical “non-responders” is to do with what is called the microbiome.  This is the population of microbes living on an in us, especially in the gut.   We each have around 10 trillion cells in our bodies, but we act as host to around 100 trillion bacteria.  The gut alone, which includes our stomach and intestines, is home to about three pounds of bacteria.   It is now recognised that these microbes play an important role in maintaining a healthy immune system and that an imbalance in gut bacteria could contribute to a “misfiring” of the system so that the body attacks its own tissues (autoimmune disease).  This results in the typical inflammatory response of psoriasis.  So what has this to do with weight loss surgery?

It turns out that bariatric surgery (particularly gastric bypass) can alter the microbiome, but it may not be to the same degree in all patients.  This variation could therefore explain why some patients undergoing bariatric surgery do not experience any benefit or may even experience a worsening of their psoriasis.   Put simply, the ultimate effect of a surgical weight loss procedure on psoriasis, may be largely determined by an individual’s gut bacteria.   This in turn raises fascinating questions about the microbiome and whether there are ways to harness it in the treatment and maybe even prevention of psoriasis.  

Dr David Ashton
12 April 2016


  • Sethi M, et al.  Clinical improvements in psoriasis and psoriatic arthritis with surgical weight loss.  ACR 2015;  Abstract 688.
  • Sako EY, Famenini S, Wu JJ.  Bariatric surgery and psoriasis.  J Am Acad Dermatol. 2014; 70: 774–779