Junk food exacerbates arthritis and joint pain, new research has found.
The study shows that bacteria in the gut appears to be the driving force behind inflammation that leads to painful "wear and tear"
of the bones in overweight people.
Osteoarthritis was long assumed
to simply be a consequence of undue stress on the joints, and that losing weight could prevent the condition.
But the new study, published today by the University of Rochester Medical Center, suggests that balancing gut bacteria with a prebiotic supplement reversed the symptoms in mice - even if their weight stayed the same.
Study leader Associate Professor Michael Zuscik said: "Cartilage is both a cushion and lubricant, supporting friction-free joint movements.
"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."
The researchers fed mice a high fat diet akin to a Western "cheeseburger and milkshake" diet.
Just 12 weeks of the high fat diet made mice obese and diabetic, nearly doubling their body fat percentage compared to mice fed a low fat, healthy diet.
Their colons were 'dominated" by pro-inflammatory bacteria, and almost completely lacked certain beneficial, probiotic bacteria, such as the common yogurt additive Bifidobateria.
The changes in the gut microbiomes of the mice coincided with signs of body-wide inflammation, including in their knees where the researchers induced osteoarthritis with a meniscal tear, a common athletic injury known to cause osteoarthritis.
Compared to lean mice, the findings showed that osteoarthritis progressed much more quickly in the obese mice, with nearly all of their cartilage disappearing within 12 weeks of the tear.
Surprisingly, the researchers found that the effects of obesity on gut bacteria, inflammation, and osteoarthritis were completely prevented when the high fat diet of obese mice was supplemented with a common prebiotic, called oligofructose.
The knee cartilage of obese mice who ate the oligofructose supplement was indistinguishable from that of the lean mice.
Prebiotics, such as oligofructose, cannot be digested by rodents or humans, but they are welcome treats for certain types of beneficial gut bacteria, such as Bifidobacteria.
Colonies of those bacteria chowed down and grew, taking over the guts of obese mice and crowding out bad actors, such as pro-inflammatory bacteria.
That, in turn, decreased systemic inflammation and slowed cartilage breakdown in the mice's osteoarthritic knees.
Oligofructose even made the obese mice less diabetic, but there was one thing the dietary supplement didn't change: body weight.
Obese mice given oligofructose remained obese, bearing the same load on their joints, yet their joints were healthier.
Just reducing inflammation was enough to protect joint cartilage from degeneration, supporting the idea that inflammation - not biomechanical forces - drive osteoarthritis and joint degeneration.
Study co-author Professor Robert Mooney said: "That reinforces the idea that osteoarthritis is another secondary complication of obesity - just like diabetes, heart disease, and stroke, which all have inflammation as part of their cause.
"Perhaps, they all share a similar root, and the microbiome might be that common root."
Though there are parallels between mouse and human microbiomes, the researchers said that the bacteria that protected mice from obesity-related osteoarthritis may differ from the bacteria that could help humans.
Now they plan to continue the research in humans.
The team hopes to compare older people who have obesity-related osteoarthritis to those who don't to further identify the connections between gut microbes and joints.
They also hope to test whether prebiotic or probiotic supplements that shape the gut microbiome can have similar effects in older people suffering from osteoarthritis as they did in mice.
Study first author Dr Eric Schott, added: "There are no treatments that can slow progression of osteoarthritis - and definitely nothing reverses it.
"But this study sets the stage to develop therapies that target the microbiome and actually treat the disease."