There's good fat, and there's bad fat – although we mostly only hear about the latter. Finding ways to decrease levels of bad (white) fat and increase good (brown) fat could help us lose weight and avoid obesity-related illness, and now researchers at Columbia Engineering have developed a transplant method, where white fat is removed from the body, cultivated in a lab for a few weeks, then reinserted into the body as brown fat.

Besides the color, the difference between the two types of fat lies in their function. White fat stores excess energy as lipids, and can be difficult to get rid of once it starts building up. Meanwhile, brown fat doesn't stick around as long, since it has higher levels of mitochondria that burn away the fat to provide energy and body heat.

Over the last few years, scientists have been experimenting with ways to turn white fat brown. That has included blocking the function of certain proteins, hormones that mimic exercise, nanoparticle injections, drugs and gene therapies that could act like a "fat switch."

But these techniques could have side effects, or be fairly invasive. The Columbia researchers realized they could have more control over the process if they conducted the conversion outside the body. To do so, they adapted a fat-grafting procedure commonly used in cosmetic surgery, where fat is removed from under the skin and then reintroduced into another part of the body.

In this case, however, the Columbia team added an extra step while the fat was outside the body – converting it from white to brown. Over the course of one to three weeks, the researchers gathered white fat tissue from mice, and cultured it in media containing growth factors and other compounds that would stimulate the "browning" process.

By keeping watch for key brown fat biomarkers, such as increased mitochondrial activity and the protein marker UCP1, the researchers found that the technique was effectively turning the bad fat good. After returning it to the animals' bodies, they found that the brown fat remained stable for the two months that the experiment ran for.

"The persistence of the converted brown fat is very important because we know that when white fat is naturally stimulated to turn to brown fat in vivo, through cold exposure for example, it can rapidly change back when the stimulation is removed," says Brian Gillette, co-author of the study. "Even though we could repeat the procedure several times if we needed to, since it's minimally invasive, it is critical that the brown fat survives well and remains stable so that it can function as an effective therapy."

A follow-up test then found that the process worked just as well on human fat. The researchers say this suggests that one day the technique could be a viable treatment for weight loss, managing blood glucose, or treating other obesity-related health problems.

"Our approach to increasing brown fat is potentially safer than drugs because the only thing going into patients is their own tissue, and it's highly controllable because we can tune the amount of brown fat we inject," says Sam Sia, lead researcher on the study. "The process is also so simple that it could be potentially performed using an automated system within a doctor's office or clinic."

The research was published in the journal Scientific Reports. The video below shows the fat turning from white to brown in the dish.