A Nimble Mind Trapped in an Awkward Body

"Quite simply, we have found support for the existence of internal bathroom scales."
"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."
John-Olov Jansson, University of Gothenberg, Sweden

"[One theory is that the internal scales] give an inaccurately low measure when you sit down. As a result you eat more and gain weight."
Claes Ohlsson, study co-author

Researchers at Sahlgrenska Academy, University of Gothenburg, Sweden, have found evidence for the existence of an internal body weight sensing system. This system operates like bathroom scales, registering body weight and thereby fat mass. More knowledge about the sensing mechanism could lead to a better understanding of the causes of obesity as well as new anti-obesity drugs.

So imagine, if you will, we animals who call ourselves human have been equipped with a "gravitostat", whose function is similar in a sense to a bathroom scale. When we step on that scale and see our weight moving northward, we tell ourselves, 'uh-oh! better watch what we're eating'. In a like fashion, the biological scale has a specific function, keeping tabs on our weight and sending a message to our brain that we've eaten enough, time to push away from the table.

The scientists that studied this issue have postulated that cells in weight-bearing skeletal bones called osteocytes produce a protein whose function is to signal the brain to stop eating. In people who are obese, it seems obvious that the cells have become inoperative. The theory floats around that too much sitting helps to add adipose tissue to our bodies, and this seems to fit right into the researchers' conclusions.

Experimentally, the researchers, using the animal-model laboratory rodents provided to them by the Lunenfeld-Tanenbaum Research Institute in Toronto, implanted capsules weighing 15 percent of their body weight into the rats' and mice's abdomens. (In equivalent weights humans would be implanted with somewhere around a 10-kg weight within the abdomen of  a 70-kg individual.) Experimental control animal counterparts had empty capsules implanted weighing 3 percent of their body weight.

Body weight in both the rats and mice with the additional loads saw body weight decrease, with total body weight (biological body weight, plus capsule weight) was similar in both groups of rodents after two weeks' elapse. As much weight was lost by the artificially loaded rodents matching what had been added; the animals simply ate less, resulting in a reduction in the amount of white adipose tissue, 'bad' fat that hoards calories.

Once the tiny weights were removed, the mice gained body weight and fat mass "demonstrating that the body weight sensor is functional in both directions", wrote the research team in their study published in the Proceedings of the National Academy of Sciences. Although rodents are most commonly used as animal models before research is conducted in humans to judge impacts, mice and rats are not humans and what works with one species will not necessarily match what is found in another animal species.

"As much as we'd love to advise people to strap on some extra weights and off you go -- you'll be less hungry and you'll lose weight -- we have no idea whether or not this would carry over into humans."
"But it does make a little bit of sense that we would have multiple ways that we sense how much we weigh and regulate that."
"If we said to a bunch of scientists who study body weight and appetite today, 'did you know that your bone cells send a signal to your brain to control your appetite', the answer before this paper was published would be 'no'."
Dr. Daniel Drucker, Lunenfelt-Tanenbaum Research Institute, Toronto

Although the actual biological mechanism remains elusive to science, the findings were similar whether testing normal mice, obese mice fed high-fat diets or mice lacking leptin, the hormone whose function is thought to suppress appetite. What is immensely fascinating is that if this process holds true and all humans are biologically outfitted with this weight-management mechanism, why is there such an epidemic of obesity?

Is the communication corridor from bone cells signalling the brain to withhold hunger symptoms when the weight metering mechanism has been triggered because of an increased load, somehow disturbed on such a wide societal scale, and why? Dr. Drucker, groping for a response that seems reasonable feels the signalling system from the bones somehow misfires "and that's why simply carrying around more weight when you're obese doesn't automatically shut off your appetite".

A response that might seem unhelpfully trite to those struggling to come to terms with their misbehaving bodies.

Shao Qian (R) and an unidentified reporter pose for a picture after Shao wins the Fat and Happy contest in Xi'an, Shaanxi province, Aug 10, 2012. Shao, 21, weighs 182 kilograms. The contest, organized by a local newspaper, aims at encouraging the overweighed to better engage in public activities. [Photo by Li Jie/Asianewsphoto]