When researchers pored over data from more than 50 cohorts of a combined nearly 20,000 patients, they found an association between obesity and less effectiveness of tumour necrosis factor inhibitors (TNFi). That was true for rheumatic disease patients, but not those with inflammatory bowel disease, they wrote in a meta-analysis in PLoS One.

“While the negative impact of obesity in patients with psoriasis is well-known, our observations that obesity uniformly results in inferior response to anti-TNF therapy across all rheumatic diseases that we studied has important implications for both clinical practice and clinical trial design,” wrote Siddharth Singh, of the University of California, San Diego School of Medicine, and colleagues.

TNFi are a type of drug which target a protein called Tumor Necrosis Factor, which causes inflammation, and thus halt the progression of disease, according to the American College of Rheumatology. “In healthy individuals, excess TNF in the blood is blocked naturally, but in those who have rheumatic conditions, higher levels of TNF in the blood lead to more inflammation and persistent symptoms,” the ACR states. “They can alter a disease’s effect on the body by controlling inflammation in the joints, gastrointestinal tract, and skin.”

[Learn more about TNFi here.]

In the PLos One study, researchers report that obesity was associated with a 60 percent greater chance of TNFi failure for patients with rheumatoid arthritis, spondyloarthropathies, psoriasis, and psoriatic arthritis, but not inflammatory bowel disease — all when compared with patients who were not obese. And the more severe the obesity, they found, the likelier that the anti-TNF drugs (infliximab, adalimumab, certolizumab pegol, golimumab, and etanercept) wouldn’t work.

“In clinical practice, physicians may consider aggressive treatment and close proactive monitoring in patients with obesity treated with anti-TNF agents such as empirically using higher dose of anti-TNF agent in obese patients, frequent therapeutic drug monitoring and/or use of combination therapy with immunomodulators to increase drug concentration and decrease risk of immunogenicity,” the researchers wrote in the study.

“We still don’t completely understand the interaction between obesity and IBD, but we know that obesity can complicate surgery,” the Mayo Clinic’s Edward Loftus, Jr. told MedPage Today. “We need to look at a bigger sample size in large observational studies. This chapter on obesity and IBD has not been fully written, and as gastroenterologists, we should still be counseling our patients to restrict caloric intake and increase physical activity as ways to combat obesity.”