It's well known that obesity and diabetes often go hand-in-hand. Over 60 million Americans are obese, a condition that makes it 20 to 40 times more likely that you'll develop diabetes than someone of a healthy weight, according to the Harvard School of Public Health. Even being overweight (as opposed to obese) increases your risk of type 2 diabetes seven-fold.



Still, while epidemic numbers of Americans--nearly 20 million--have diabetes, it is not known why some obese people develop diabetes, while others never do.

A Hormone Called Leptin

The protein hormone leptin--which comes from the Greek word for "thin," leptos--may hold the key to unlocking some of this mystery. Derived from fat cells, defects in leptin signaling may lead to obesity, overeating and less energy expenditure.

According to metabolic specialist Ron Rosedale, M.D.:

"Leptin is the way that your fat stores speak to your brain to let your brain know how much energy is available and, very importantly, what to do with it. Studies have shown that leptin plays significant, if not primary, roles in heart disease, obesity, diabetes, osteoporosis, autoimmune diseases, reproductive disorders, and perhaps the rate of aging itself."

Further, a study on mice published in Cell Metabolism has revealed that leptin plays a role in regulating blood sugar, which it does via two brain-body pathways:

One that controls appetite and fat storage

One that tells the liver what to do with its glucose reserves

If the first pathway (the one involving appetite and fat storage) is disrupted, obesity is expected, which raises the risk of diabetes. However, the study found that both pathways may have to be disrupted in order for the body to lose control of insulin and blood sugar levels and develop diabetes.

"Taken together, our findings show there's more to the obesity-diabetes link than the classic thinking that if you eat too much sugar, you'll get fat and get diabetes and that if you don't get diabetes, it's only because you're making more insulin to keep up with the sugar," says senior author Martin G. Myers, Jr., M.D., Ph.D., of the University of Michigan Medical School. "There's something else contributing. Now the challenge is to find out what that is."

Leptin's Link to Fat and Diabetes

"If a person is getting too fat, the extra fat produces more leptin, which is supposed to tell an area of the brain in the hypothalamus that there is too much fat stored, more should not be stored, and the excess burned," Rosedale says.

"Therefore, signals are sent to stop being hungry, to stop eating, to stop storing fat and to start burning some extra fat off. More recently, it has been found that leptin not only changes brain chemistry, but can also "rewire" these very important areas of the brain that control hunger and metabolism," he continues.

In fact, it is also possible to become leptin-resistant. How this process occurs is the focus of much research, but Rosedale suggests that leptin-resistance is similar to insulin-resistance in that it occurs after being overexposed to high levels of the hormone. At this point, the body no longer responds to the hormone, much like you no longer notice a bad odor after being exposed to it for a while, Rosedale explained.

Much like high blood sugar levels result in surges in insulin, sugar metabolized in fat cells causes the fat to release surges in leptin. Over time, leptin-resistance may develop.

Can Leptin be Used to Help Lose Weight or Prevent Diabetes?

As it stands, leptin is still a mysterious hormone that researchers are trying to sort out. To put it simply, though, overweight people tend to have very low levels of leptin in their systems (they may have disruptions in leptin signaling or they may be leptin-resistant, for instance). And, studies have found that feeding leptin to overweight mice causes them to lose weight. This effect was not observed in humans, however.

For now, the best way to reduce your chances of diabetes and obesity (and other diseases like heart disease and accelerated aging), according to Rosedale, is to avoid surges in leptin (which can eventually make you leptin-resistant).

Eating the typical American diet, full of refined sugars and other processed foods, is a surefire way to cause surges in leptin. Focusing your diet on simple, mostly unprocessed foods like vegetables is currently the best way to reduce surges in leptin and leptin-resistance, Rosedale says.

So for now there is no magic leptin injection or pill to make you lose weight and prevent diabetes. The good old advice of eating a healthy diet, though, will help to keep your leptin levels normal, which is key to a healthy weight and life.