Bone is super-interesting, but not an energy sink

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Natalie Angier’s article, “Bone, a masterpiece of elastic strength,” is pretty cool. It describes the case of Harry Eastlack, a sufferer from fibrodysplasia ossificans progressiva, a kind of ossification of the soft tissues. I’ve seen his skeleton at the Mutter Museum, it’s incredible the extent to which bone invaded the rest of his body. It’s a great opportunity for her to talk about the constant reconstruction process of the skeleton:

Bone also has a crack repair team, in every sense of the word: osteoclast cells that dig around the cracks, using acids to wipe away the old matrix, and osteoblast cells that migrate in and secrete fresh spacklings of bone. Bone remodeling is going on simultaneously in hundreds of locations a day, Dr. Karsenty said. Its our private MASH, he said, our ambulatory surgical unit that helps keep us on our feet.

I had to comment though, because of this:

But like all forms of health care, bone repair doesnt come cheap, and maintaining skeletal integrity consumes maybe 40 percent of our average caloric budget.

Not a chance. Now, the stuff about hormonal communciation between bone and gut is true, and is a very current line of research. But 40 percent of BMR? I haven’t found yet a reference that lists the mass-specific energy consumption of bone tissue – it’s such a small component of the body’s energy budget that nobody bothers. Rolfe and Brown (1997) review energy metabolism of different tissues, listing liver, GI tract, kidney, lung, heart, brain, and skeletal muscle which sum up to 88 percent of oxygen use in humans. That leaves 12 percent for everything else, including two high-mass tissues, bone and skin. Heck the paper lists extra bone as one reason why bigger animals have lower mass-specific energy requirements!

So no, bone is not drawing 40 percent of your caloric budget. However, your brain is drawing 20 percent.

References:

Rolfe DFS, Brown GC. 1997. Cellular energy utilization and molecular origin of standard metabolic rate in mammals. Physiol Rev 77:731-758. Abstract