April 19 (UPI) -- A high-fat diet, such as a cheeseburger and milkshake, has been linked to arthritis and joint pain, according to a study of mice.
Researchers at the University of Rochester Medical Center determined that bacteria in the gut from a high-fat diet could causing osteoarthritis, a common side effect of obesity. The findings were published Thursday in the journal JCI Insight.
"There are no treatments that can slow progression of osteoarthritis -- and definitely nothing reverses it," first author Dr. Eric Schott, a postdoctoral fellow in the CMSR and soon-to-be clinical research scientist at Solarea Bio, Inc. said in a press release. "But this study sets the stage to develop therapies that target the microbiome and actually treat the disease."
About 54 million adults in the United States have doctor-diagnosed arthritis, including 31 million people with osteoarthritis, according to the Arthritis Foundation.
Originally, it was thought that obesity caused "wear and tear" on the body, leading to osteoarthritis, including arthritis.
But the researchers found that wasn't the case in studying mice.
They found that obese mice had more harmful bacteria in their guts than lean mice. A common prebiotic supplement did not help the mice shed weight, instead reversing other symptoms. The guts and joints of obese mice were the same as from lean mice.
The mice were fed high-fat meals akin to a Western cheeseburger-and-milkshake diet.
In 12 weeks, the mice nearly doubled their body fat percentage compared with mice fed a low-fat, healthy diet. Pro-inflammatory bacteria was dominant in their colons, completely lacking certain beneficial, probiotic bacteria, including common yogurt additive Bifidobateria.
The mice had simultaneous inflammation throughout their body, including in their knees, where the researchers induced osteoarthritis with a meniscal tear. Nearly all of their cartilage disappeared within 12 weeks of the tear.
"Cartilage is both a cushion and lubricant, supporting friction-free joint movements," Dr. Michael Zuscik, associate professor of orthopedics at CMSR, said. "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."
Prebiotics, including oligofructose, made the obese mice less diabetic but their body weight didn't change.
"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," Dr. Robert Mooney, professor of pathology and laboratory medicine at CMSR, said. "Perhaps, they all share a similar root, and the microbiome might be that common root."
But bacteria that protected mice from obesity-related osteoarthritis may differ from those that could help humans. The researchers are working with the U.S. Department of Veteran's Affairs to study this situation in veterans.