Despite a seemingly obvious connection between back pain and obesity, there’s nothing obvious about it. Hussain et al found a clear link, but not for the reason everyone assumes. Dario et al found no link at all, despite looking extremely carefully.
Back pain and metabolism, not mechanics
Hussain et al. shows evidence of the metabolic roots of back pain, and maybe other kinds of chronic pain as well. The majority (82%) of 5000 Australians reported back pain on a questionnaire, and in 27% of them it was bad enough to be disabling. When compared to their fat mass fat distribution — known indicators of metabolic disorders — a clear pattern emerged: back pain intensity and disability go up with measures of fat mass and distribution.
This data does not suggest that weight is a “mechanical” problem — greater weight causing greater stress on spinal joints — but rather that “systemic metabolic factors associated with adiposity play a major role in the pathogenesis of LBP.”
This is a great example of what I mean when I say (and I often do) that we need to look beyond biomechanics — way beyond — to the messy “wet” factors in chronic pain.
That sounds very much like the last word, but this is musculoskeletal medicine, where nothing is straightforward.
No link at all in a big new twin study
Specifically because “current evidence remains unclear,” Dario et al. tried to get everything right: a long-term study of over a thousand initially healthy people, measuring both the overall amount of fat as well its distribution, and — this is important — using twins to control for “the possible effects of genetic and early shared environmental factors.” This is an advanced approach.
And the results? They found … nothing: “No increase in the risk of chronic LBP was found for any of the obesity-related measures.” They checked six ways from Sunday, and “obesity-related measures did not increase the risk of developing chronic low back pain.”
So where does that leave us? Still in the woods. The relationship between back pain and obesity has always been — and remains — a bit of a question mark. My best guess is that there is no link, or only a weak one, and it’s explained by metabolism, not the stress applied to your spine by extra weight. This fits right in with many other counter-intuitive truths about back pain, like the fact that sitting isn’t a risk factor, its bark is almost always worse than its bite, we really don’t need to be taught good lifting technique.