Fat acts as an energy storage container normally comprising about 20 to 25% of the human body weight. Twenty years ago scientists identified a hormone called leptin produced by fat cells at levels proportional to the amount of fat in the body, thus informing the brain of how much fat is around.
Leptin is supposed to preserve the body’s fat mass within a relatively narrow range. Low leptin levels increase appetite and reduce basal metabolism, whereas high leptin levels blunt appetite and promote fat breakdown.
Appropriately the word leptin says it all if you’re Greek, it means thin. If all is working fine, which it doesn’t for all, it should inhibit hunger, thus keeping you thin. On the contrary, the hunger hormone ghrelin instead increases appetite. Together they regulate the energy balance to keep body weight under close control (you wish).
Scientists identify the leptin pathway
In some way leptin-induced brain activity lead to fat breakdown, but until now it has been unclear how the brain signals back to the fat tissue to achieve this effect. Now, a breakthrough study by scientists from Portugal and the USA has identified sympathetic nerves in white fat tissue and found that direct stimulation of these neurons is sufficient to induce fat breakdown. This is called a neuro-endocrine loop.
The local activation of these neurons releases norepinephrine, a neurotransmitter, that in turn triggers a cascade of signals in fat cells leading to fat hydrolysis. Without these neurons, leptin is unable to drive fat-breakdown.
One factor in the obesity epidemic
Now, unfortunately, some people are affected by central leptin resistance, a condition in which the brains of those people are insensitive to leptin leading to increases in weight and ultimately one reason for overweight and obesity. Since the sympathetic nervous system is autonomous there is no way of consciously influencing its activity. Sorry.
But scientists now have an entry point for developing a treatment of the condition, at least one piece of the puzzle to come to grips with the multifactorial obesity epidemic.