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Where Does Fat Go When You Lose Weight? Mostly Into Thin Air

(Phoney Nickle/Flickr)

(Phoney Nickle/Flickr)

By Richard Knox

A couple of years ago, Ruben Meerman took off 40 pounds. And that got him wondering: What exactly happened to all that fat?

Conventional wisdom was that he “burned” it off. Or sweated it off. Or excreted it. None of that satisfied Meerman, who has a physics degree and makes his living explaining science to schoolkids and for the Australian Broadcasting Corporation.

So Meerman tackled the problem and eventually came up with a surprising answer: Most of the lost fat disappears into thin air.

More specifically, 84 percent of those fat molecules get exhaled as colorless, odorless carbon dioxide. The other 16 percent departs the body as H-2-O — plain old water.

Meerman says the discovery “got me really excited because I’d stumbled onto a gap in the knowledge. It struck me as remarkable that no one had thought this was interesting enough to pursue.”

The British Medical Journal thought so too. It has published a paper, co-authored by biochemist Andrew Brown of the University of South Wales, in its annual Christmas issue, which features off-beat (but peer-reviewed) research.

Weight Loss Realism

Meerman hopes the work will dispel misconceptions held by health professionals as well as the general public. And, he hopes it will provide a helpful dose of realism to counter the impossible expectations millions have about weight loss.

If people understand where the fat goes (and how), they’ll get “why there’s a limit to how quickly you can lose weight,” Meerman said in a Skype interview from Sydney. “And if you understand the limit, you won’t be so quickly depressed if you don’t lose 20 pounds in the first two weeks.”

First, the misconceptions. Meerman and Brown surveyed 150 professionals — split equally among family doctors, dietitians and personal trainers — about where they think the fat goes during weight loss.

By far the most common answer was that the fat was transformed into energy or heat — that is, “burned off.” About two-thirds of doctors thought so. A slightly higher proportion of dietitians did too, and about 55 percent of personal trainers.

But that would violate the Law of Conservation of Mass. It’s a basic precept of chemistry, formulated in 1789 by the French scientist Antoine Lavoisier, which holds that mass is neither created nor destroyed in chemical reactions. The total mass at the end must equal the mass at the starting point — even if matter is quite transformed in the process, from solid to liquid or gas.

The Energy Of A Bomb

Meerman points out that if fat were transformed into pure energy during weight loss, the results would be cataclysmic. Continue reading

Perspiration Power: Scientists Turn Sweat Into Electrical Energy

A tattoo biosensor (enlarged above) detects lactate levels during exercise; a biobattery using the technology could power electronics (Photo: Joseph Wang)

A tattoo biosensor (enlarged above) detects lactate levels during exercise; a biobattery using the technology could power electronics (Joseph Wang)

By Richard Knox

It takes energy to work up a sweat. But now researchers have cleverly figured out how to turn sweat into energy.

Scientists have devised a small skin patch they call a “temporary tattoo” that can transform lactate — one of 800 or so chemicals in sweat — into electrical energy.

Not much energy, so far. Only about 4 microwatts, less than half of what it takes to power a digital watch. But the energy alchemists are confident they can scale up their sweat “biobattery” enough to play an iPod, power a GPS device, or warn a marathoner when it’s time to top up her electrolytes.

The researchers think their work could also have military and biomedical applications, if they can tweak the technology to squeeze more electricity out of sweat.

“Sweat has been largely neglected, not thought of as a worthwhile physiological fluid.”

– Researcher Josh Windmiller

“Right now we’re working on the biofuel cell so it can get higher power,” Wenzhao Jia, of the University of California San Diego, tells CommonHealth. She’s describing the skin-patch biobattery tomorrow at a meeting of the American Chemical Society in San Francisco.

One problem in experiments so far: People who are less fit produce more energy from their sweat than those who are moderately fit. The fittest subjects produce the least amount of power. The researchers are trying to figure out how to compensate for this.

“We want to integrate another electronic element such as a super-capacitor that can store the power,” Jia says. “Ultimately, we can connect a number of cells together to make the current higher.”

Jia says the sweat-powered battery grew out of an earlier effort to monitor levels of lactate, a metabolic byproduct when sugar (glucose) is broken down to produce energy — a process called glycolysis. (It’s the buildup of lactate, or lactic acid, that makes your muscles sore after strenuous exercise.) Continue reading