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Dr Drucker

A new study published recently in the Proceedings of the National Academy of Sciences may give new weight to the notion of “heavy bones”!

Dr. Daniel Drucker of the Lunenfeld-Tanenbaum Research Institute, part of Sinai Health System, was one of the scientists involved in the study. He explains that the focus was on one simple question: Does your actual body mass affect how much you eat and, ultimately, how much you weigh?

For the study, the researchers implanted into the abdomens of rats and mice capsules that weighed 15 per cent of the body weight of each animal. “Control” animals were implanted with an empty capsule equivalent to only three percent of their body weight.

After two weeks, the total body weight was similar in both groups. The artificially loaded rodents lost about as much weight as had been added and, once the miniature weights were removed, there was a gain in body weight and fat mass.

The scientists think that osteocytes, specialized cells in weight-bearing bones, act as an internal body weight sensor — a “gravitostat” that sends signals to the brain to eat less.

Todays’ typically sedentary lifestyle may play an important role. “The weight of the body is registered in the lower extremities. If the body weight tends to increase, a signal is sent to the brain to decrease food intake and keep the body weight constant,” explains co-author John-Olov Jansson, of the University of Gothenburg. Sitting may make the brain think the body isn’t as heavy as it actually is.

Still, “as much as we’d love to advise people to strap on some extra weights and off you go — we have no idea whether or not this would carry over into humans,” cautions Dr. Drucker.

The precise mechanism still isn’t clear — nor is the jump from well-regulated weight to obesity. When the team used genetic techniques to deplete the mice of osteocytes, the effect went away. Drucker’s hypothesis is that the signalling system from the bones is defective in obesity, “and that’s why simply carrying around more weight when you’re obese doesn’t automatically shut off your appetite.”

If the research holds up in humans and if scientists discover what kind of “magical factor” the bone cells might be producing, theoretically it could lead to new treatments for obesity, Drucker said.