Standing to lose weight
The body has its own weight-measuring scale and it’s in the feet!
Prolonged sitting is associated with an increased risk for obesity, and some research suggests that this increased risk is independent of physical activity (1,2). In a recent study published in the Proceedings of the National Academy of Sciences, an international team of researchers discovered that standing, at least in mice, activates an “internal bathroom scale,” a homeostatic mechanism that detects changes in weight and regulates body weight by sending signals to the brain to either eat more or less (3).
The last time an entirely new body fat regulatory process was identified was in 1994, with the discovery of leptin, a hormone secreted by fat cells. Increasing the number of fat cells causes an increase in leptin, which then travels to the hypothalamus to signal the brain to eat less. Despite its involvement in body weight regulation and years of research, the discovery of leptin didn’t lead to any new obesity treatments.
“Very often several different mechanisms work together to regulate a physiological process, and it seems as if leptin by itself cannot cure human obesity,” said co-author Claes Ohlsson from the University of Gothenburg, Sweden.
Ohlsson and colleagues wanted to determine what additional mechanisms besides leptin regulate fat mass and body weight. To research this, they turned to mice and rats with diet-induced obesity. The team implanted capsules weighing 15% of the animals’ body weight into their abdomens and empty capsules into control animals. Surprisingly, the body fat of animals carrying the weighted capsules decreased by the exact same weight of the capsules added!
“We were surprised that the effect seems to be completely independent of leptin,” said Ohlsson. In fact, further experiments showed that the mechanism is regulated in part by a unique load-sensing cell type—osteocytes—located in foot bones.
Previous research suggested that osteocytes regulate bone mass by “sensing” short-term high impact changes in body weight. “We therefore hypothesized that sustained slightly increased loading also might exert its effect on body weight via sensing by osteocytes,” said Ohlsson.
The team repeated the experiments, but this time they added weight capsules to mice without osteocytes. These mice did not change their eating patterns to account for the extra weight, confirming a role for osteocytes in homeostatic body weight regulation.
Osteocytes may not be the only players in the body’s weight sensing capabilities. Ohlsson and colleagues believe that there is also a biological “sensor,” that depends on osteocytes. They are presently hunting for that sensor and hope to soon identify the detailed mechanisms involved in this newly discovered homeostat.
Ohlsson cautioned that there are other factors to consider before we all start standing to lose weight. For example, body weight fluctuates despite the existence of homeostatic body weight regulation. “Homeostatic mechanisms try to keep the phenotype constant, but like for most diseases, the different homeostatic mechanisms are not perfect in all subjects as a result of environmental and/or genetic differences,” said Ohlsson.
Additionally, it remains to be seen if this homeostat also exists in humans. “We hope so, but we do not know yet,” said Ohlsson.
