Those aggravating pests known as fruit flies are helping researchers at Fred Hutchinson Cancer Research Center in Seattle try to solve the puzzle of why some people are fat and some are not.

It turns out fruit flies have a nearly identical biological response to obesity as humans, including high cholesterol and diabetes.

“You're taking in food via your gut, but it's being stored in a different part of your body and actually for you to function well all of this information needs to be communicated to the brain so that you can decide whether you have enough energy to make that walk up the hill,” said Dr. Akhila Rajan, Assistant member of the basic sciences division at Fred Hutch

Whether you are highly active or spending the day on the couch our bodies are steadily working to balance food intake with energy output, but we all have different energy needs, so how does our body know?

“So you want to build a bridge from place A to place B and you want to know exactly where the bridge has to go through. Using the fly system helps you draw that linear wiring diagram. Which may or may not work out exactly in humans but at least you know there's a map. At least you know Google is taking you from point A to point B on this bridge, and the fly system helps to do that,” Rajan said.

When Dr. Rajan says fly system, she’s literally talking about fruit flies.

It may seem obvious. If you feed a fly candy, it’ll get fat. But more importantly -- why? Dr. Rajan thinks the answer is in the hormone called Leptin. It helps our bodies regulate weight by telling our brain when we've eaten enough. Somewhere between the slice of pizza and french fries, that message is being lost leading to obesity.

“So, what happens in obese people is that this hormone is not able to reach your brain properly and inform the brain that it has a food resource," Rajan said. "I think of it as this hormone as a supervisor of how much energy you have in your entire body and that's Leptin."

So how do the flies help?

“We are using the fly system to try and understand how each of these processes occurs. It's almost like trying to use flies as a tiny test tube because it has everything we humans do have metabolically speaking and using them as a system to just very specifically test out will this kind of manipulation in a diet make things work better,” Rajan said.

With the help of fruit flies, researchers have been able to track the pathways and map the messaging system from the stomach to the brain. With that information, they hope to learn what causes the communication breakdown.

Going forward, Rajan says this information could one day be used to design a drug that can combat obesity. The bottom line: the better we understand the science of how the body works, the better chance we have of beating the obesity epidemic