The Physics of Fat
What happens to the weight we lose, and how does it escape the body?

Robyn Williams: Ockham's Razor here is presented by Ruben Meerman.

Meerman: now that's an interesting name — Dutch, of course, Ruben was born in Holland. But Meerman sounds very much like the male version of mermaid — which fits, because Ruben is best known as the 'Surfing Scientist' and lives in the ocean. You've seen him on Catalyst no doubt, applying physics to his surf board.

Now being fit and so vital, he's even appeared with Tom Cruise in Mission Impossible, so you wouldn't think that Ruben is concerned about his own weight. Well, maybe not so much, but he's very interested in where the excess goes when you get rid of it. Hence, his new book.

Ruben Meerman: When you lose weight, where does it go? The fat, I mean.

Imagine for a moment that you’ve just lost 10 kilograms of fat from your adipose tissue. Congratulations! Your friends would want to know how you did it. What’s your secret, they’d say. Did you quit sugar? Did you join weight watchers? Or weight lifters?

Well, I’m a physicist, by training, so I’m interested in something a bit more fundamental. Ten kilograms is an awful lot of yourself to ‘misplace’ — a whole toddler worth of flesh — so my question is this; where, out there in the cosmos, did that 10 kilograms of fat go? What happens to the weight we lose, and how does it escape the body?

I asked 150 doctors, dietitians and personal trainers this question in 2014 and their answers were, quite frankly, shocking. Only three of them got it right! The most common misconception I encountered was that fat is converted to energy or heat. The problem with this is theory, however, is that human beings, and fat, are made of atoms. That’s why you weigh something instead of nothing.

It’s true that we talk about burning fat, and that we balance our diets by comparing the energy we put in with the energy we put out, but Einstein showed us that E = mc2. Therefore, if 10 kilograms of fat really did turn into kilojoules, the energy released would be equivalent to 15,000 times the yield of the atomic bomb detonated over Hiroshima. It sounds ridiculous, because it is. Humans lose weight biochemically, not relativistically.

Some of the health professionals I surveyed thought that the metabolites of fat metabolism are flushed down the toilet, revealing deep misconceptions about the human digestive system. A few even believed that fat is converted to muscle, the problem being that triglyceride is made of carbon, hydrogen and oxygen, and the human body cannot transmute those elements to make the nitrogen or sulphur atoms required to make protein.

So if it doesn’t vanish into the ether, the sewers or muscles, where does fat go? I’ll never forget the day I first thought about this question. Like two thirds of Australians, my body mass index had crept over the recommended weight for my height and by the age of 42, I was 5 kilograms heavier than the World Health Organisation’s recommendation. I was also a smoker, which is an embarrassing secret I’m only declaring now to assure you that I’m not about to claim the moral high ground when it comes to health. I played Russian roulette with mine so I’m not going to lecture you about yours.

But, as a science reporter who does cute experiments on children’s television, I’m supposed to know better. So, on Christmas Eve 2012, I went cold turkey and made a New Years Resolution to get back in shape. I took the conventional advice to eat less and move more for eleven weeks, and, lo and behold, the next time I weight myself, six and a half kilos had vanished from the scales. That’s no world record, but it got me thinking. How had this happened? Where did those 6.5 kilos of flesh go?

I can’t recall the exact words I typed into my browser, but if you do a search for “weight loss” today, the Internet spews out more than 170 million results, but when I tried to find out where fat goes in 2013, all the World Wide Web gave me was the sound of crickets.

After a crash course in the hieroglyphics of biochemistry, I finally learned what really happens to fat, and it was the closest I have ever come to hearing trumpets in the sky.

It turns out that all our fat is ultimately converted to carbon dioxide and water and nothing else. I had exhaled the weight I’d lost, a few milligrams at a time, and the rest had turned into crystal clear water. What’s more, it had been happening right under my nose all along!

I always knew that I’m leaking water, but I’d never made wondered where all the carbon in my breath comes from.

Energy is indeed released in this process, and we measure this immaterial stuff in kilojoules, but the kilograms depart as CO2 and H2O. And guess what? You’re doing this too, right now! Even at rest, about 30 per cent of the carbon atoms in your breath are sourced from your fat cells.

These revelations supercharged my motivation, but then, an even more intriguing question dawned on me. If you lose 10 kilograms, I wondered, then how many of them depart as carbon dioxide, and how many become water? But, to my eternal surprise, those figures had never been published before, so I spent the next four months trying to figure it out myself. I eventually stumbled onto the clue I needed to solve this conundrum in a paper published way back in 1949, by the legendary physiologist Nathan Lifson. Using the results of his experiments with heavy oxygen in mice, I was able to show that 8.4 out of every 10 kilograms of fat is exhaled as carbon dioxide, and the rest becomes 1.6 litres of fresh water.

A year later, I had the privilege of airing my quirky calculations on Catalyst and, in the process, I met Professor Andrew Brown, who is the Head of School of Biotechnology and Biomolecular Science at the University of New South Wales. Andrew suggested we present these results to a learned journal and, lo and behold, our paper was accepted by the British Medical Journal for the 2014 Christmas Issue.

So now that you know your lungs are the primary excretory organ for weight loss, the next question is, so what? Should we be worried that the doctors, dietitians and personal trainers at the frontlines of the obesity epidemic are suffering the mass delusion that fat turns into energy, poo or muscles? Well, let’s see.

Obesity is completely avoidable and yet, in 2008, the condition cost Australia $58 billion. To put that figure into perspective, our total defence budget for the same year was $36 billion and our waistlines have not shrunk since then. Therefore, the obesity is now costing more than it does to defend our borders and stop those pesky boats full of desperate people fleeing deadly conflicts.

The reason we should care about this was summed up perfectly in a column written for the British Medical Journal by a severely obese women called Emma Lewis.

In her letter, titled “Why there is no point telling me to lose weight”, Emma lamented her distrust and lack of rapport with general practitioners because, even though the consultation might be about glandular fever or a sprained ankle, the doctor’s attention inevitably turns to her weight, even though she feels perfectly healthy. In her most heartbreaking revelation, Emma said that her doctors still think “that it’s important to tell me to do something that I know to be impossible”.

Just let that sink in for a moment. Here is an intelligent, witty, literate woman who has been led to believe that she simply cannot lose weight when, in fact, the opposite is true. This may come as a surprise to, well, everyone, but it is actually biologically impossible to not lose weight. Why? Because we all lose about 9 milligrams of carbon every time we exhale. And while human beings can stop eating for weeks or months on end, we cannot stop breathing for more than a few minutes. Therefore, we are always losing weight, 24 hours per day. The only reason that weight doesn’t stay off is because we eat and drink.

Would it help if Emma’s doctors could explain how weight loss really works at the molecular level? We have clearly failed to teach a whole generation this basic biology properly and, as a result, we are being bamboozled by an endless parade of self-proclaimed experts who claim to have found the magic bullet. You’ve heard them. Sugar is poison! Carbohydrates are more fattening than fat! We’ve all been eating the wrong way.

According to these wellness gurus, our expanding waistlines have nothing to do with the fact that we’re eating too much and not moving enough. It’s not our fault we’re fat. It’s the sugar industry. It’s multinational corporations. It’s fast food chains. But it’s not just the Paleo people and the Low-Carb Cult. Even the experts have some very peculiar ideas. Believe it or not, there are now 107 different causes of obesity in the peer-reviewed literature, and some of them are, quite frankly, hilarious. According to published research, we can blame our bulging bellies on air conditioning, celebrity chefs, outdoor advertising traffic noise and too many pictures of succulent food.

But let’s apply Ockham’s Razor here. It may well be that sinister, unidentified forces are causing two thirds of us to overeat but isn't it a bit more likely that we have simply ignored the age-old wisdom to eat less and move more because we have no idea how our bodies really work, and will therefore believe any old nonsense.

How did things get this out of hand? How could there be 107 different causes of obesity? How could doctors and dietitians end up believing magic happens inside the human body, which is what you have to believe to think that fat turns into energy. These were the brightest kids in their class at school, so the problem is clearly not their intelligence.

Something must be very wrong with the state of science education when our highest achievers are forgetting Antoine Lavoisier’s law of conservation of mass and Einstein’s theory of special relativity, two of the most important scientific discoveries ever made!

The good news is that the problem is easily fixed. Just show pour liquid nitrogen over a latex balloon full of exhaled breath and watch what happens inside. After the condensed oxygen inside all boils away, the frozen carbon dioxide left behind becomes clearly visible. If it’s your own breath in there, seeing this unfold right in front of your eyes is one of the most enlightening and transformative experiences you’ll ever have.

I’m not suggesting this amazing demonstration will solve the obesity crisis, but here’s one thing I do know: knowing what really happens to fat surely can’t make it any worse!

Robyn Williams: Probably not.

Ruben Meerman's book on this is called Big Fat Myths — well worth a look.

He studied physics at QUT, the Queensland University of Technology, a very lively campus indeed, and keeps fit on his surfboard.

So remember, eat less and move more and breathe heavily while you're at it.

Next week's Ockham's Razor is about your earliest memory — can it go back beyond the age of two? Can you recall being a tiny baby? Professor John Bradshaw thinks not. I'm Robyn Williams.

-Australian Broadcasting Corporation