Junk food-loving bacteria, not extra weight, cause arthritis and joint problems, study finds

Osteoarthritis progresses no faster in obese subjects with a healthy mix of gut microbes

Inflammation caused by unhealthy diets causes rapid loss of joint cartilage and painful knee problems (Getty)

Fast food diets are causing arthritis and debilitating joint pain but not by causing us to pile on the pounds, as scientists have shown an explosion of junk-hungry bacteria in the gut are responsible.

Osteoarthritis is one of the biggest causes of disability in higher income countries, affecting at least eight million people in the UK and 31 million in the US.

Obesity significantly increases the chances of being affected and it was thought this was due to increased wear and tear on joints like the knees.

But US researchers have shown it is the body’s response to unhealthy gut bacteria that speeds up this process, rather than the weight itself, which could mean heavy people with a balanced bacterial mix can avoid arthritis.

“There are no treatments that can slow progression of osteoarthritis – and definitely nothing reverses it,” said Dr Eric Schott from the University of Rochester Medical Centre in the US.

“But this study sets the stage to develop therapies that target the microbiome (the body’s bacterial ecosystem) and actually treat the disease.”

The findings are now being looked at by the US Department of Defence to see whether supplements to promote a healthy mix of stomach bugs can avert joint problems in veterans.

Bacteria that thrive on a high fat junk food trigger inflammation, the body’s response to stress and foreign invaders, when they build up in intestines.

This causes the immune system to attack its own cells and cartilage in joints like the knee, which are subject to a lot of wear and are particularly susceptible.

“Cartilage is both a cushion and lubricant, supporting friction-free joint movements,” said Michael Zuscik, associate professor of Orthopaedics, who led this study.

“When you lose that, it’s bone on bone, rock on rock. It’s the end of the line and you have to replace the whole joint. Preventing that from happening is what we, as osteoarthritis researchers, strive to do – to keep that cartilage.”

For the study, published today in the journal JCI Insight, the team fed mice on a high fat diet which caused them to rapidly develop twice the body fat of the control-group mice and develop diabetes.

The obese group had a much higher level of inflammation-causing bacteria than the control group, which were fed a lean diet, and osteoarthritis progressed much more quickly after they were each given an injury to their knee cartilage.

But these effects were completely neglected by introducing a “prebiotic” supplement, a sweetener called oligofructose, which encourages growth of the sort of health-promoting bifidobacteria, which is commonly added to yoghurt drinks.

These sorts of bacteria were entirely absent in the junk food group, but in the supplement group they increased rapidly. The mice which received the supplement experienced no extra wear on their joints when compared to control group and had lowering levels of the inflammation.

While the next round of trials will be needed to determine which bacteria can produce the same response in humans, the authors said their findings show osteoarthritis is “another secondary complication of obesity,” with inflammation as a root cause.