The researchers speculated that, normally, the animals’ bone cells would have provided what they called a “gravitostat,” using the body’s pressure against the earth to sense its weight and send messages to the brain about whether that weight had grown or declined. Without those bone cells at work, the rodents did not realize how heavy they had become.
People are not rodents, though, and the findings, while interesting, told us nothing about us. So, for the new study, which was published recently in EClinical Medicine, the same scientists recruited 69 overweight adults and, in lieu of lead pellets, asked them to wear weighted vests. Some of these vests added 11 percent to a person’s body weight; the others added about 1 percent and served as a control. The volunteers were asked to wear the vests throughout the day but not otherwise change their diets or lives.
After three weeks, the men and women wearing the heavier vests had dropped about three pounds of fat, on average, which was less than the weight of their vests but substantially greater than among the other group, whose weight loss was negligible. Some of this successful loss likely was a result of the fact that people in the heavier vests carried more mass now, the scientists believe, meaning they burned more calories whenever they moved.
But the results also intimate that, like the animals in the earlier experiments, humans may contain a gravitostat, says John-Olov Jansson, a professor at the University of Gothenburg who oversaw the new study. If so, our bodies and bones rely on the relative dent we make against the ground to know if our body mass has changed and if, for the sake of homeostasis, we should gain or drop a bit.
In that case, the broad implication is that we may need to stand and move in order for our gravitostat to function correctly, Dr. Jansson says. When you sit, “you confuse” the cellular sensors into thinking you are lighter than you are, he says.
The idea of an internal gravitostat is still speculative, though, he says. The researchers did not look at volunteers’ bone cells in this study. They also did not compare their diets and sitting time, although they hope to in future experiments. Plus, the study was short-term and has practical limitations. Weighted vests are cumbersome and unattractive, and some of the volunteers complained of back pain and other aches while wearing them.
But the researchers expect that wearing a weighted vest is not necessary to goose someone’s gravitostat into action, Dr. Jansson says. If they are right, getting out of your chair could be a first step toward helping your body recalibrate your waistline.