Do Bad Bugs in an Obese Gut Cause Knee Pain?

So just when I thought I had formulated the authoritative take on why obesity causes knee pain (namely, that the excess weight places too much force on vulnerable knees), along comes this study:

The gut microbiome could be the culprit behind arthritis and joint pain that plagues people who are obese, according to a new study.

Hmm. Interesting.

The study appeared in a relatively new publication called JCI Insight. You can find it here. The subjects were mice (so, possible objection number one: mice aren’t humans).

One group of mice ate high-fat foods similar to a “cheeseburger and milkshake” diet for a few months. The other group consumed low-fat, healthy meals. After 12 weeks, the chubby mice were carrying nearly twice the body fat of their lean counterparts.

Researchers noted:

Pro-inflammatory bacteria dominated their colons, which almost completely lacked certain beneficial, probiotic bacteria, like the common yogurt additive bifidobacteria.

Here’s the money paragraph of the article:

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 ... compared to lean mice, osteoarthritis progressed much more quickly in the obese mice, with nearly all of their cartilage disappearing within 12 weeks of the tear.

The researchers discovered they could prevent the destructive effects of obesity on gut bacteria, inflammation and osteoarthritis by adding oligofructose to the diet of the fat mice. Interestingly, the mice didn’t lose weight – they remained obese – but this additive preserved their knee cartilage, so it looked the same as that of the skinnier mice.

Before my heavier readers make a dash to the store, hunting for foods containing oligofructose, a word of caution:

The bacteria that protected mice from obesity-related osteoarthritis may differ from the bacteria that could help humans.

Apparently, studies using people will be forthcoming. The future studies are worth keeping an eye on. I still think the mechanical effect of obesity on knee cartilage is significant, but this at least introduces the possibility that another mechanism may be an equally big – or bigger – culprit.