The simple but difficult physics of losing weight

Following up this CT post on health living,, everyone has their own story and their own health. That’s true, but we are all subject to the same physical laws. So, here’s my story and some thoughts on the physics.

I managed to lose about 12 Kg over a couple of years, almost entirely through exercise.

The basic physics is simple
(1) weight loss = (kilojoules burnt – kilojoules consumed)*k,
(2) kilojoules burnt = base metabolism + work done

where k ≃ 0.025 is a constant reflecting the rate at which your body converts kilojoules of food energy into kilograms of fat. If you can alter the right hand side of (1) through any combination of diet and exercise then you will lose weight.

The problem is that altering either of these, or even altering while holding the other constant is really hard. Dieting makes you tired and slows your metabolism. Exercise increases your appetite, and also encourages you to flop once you stop exercising. All that’s because your body isn’t evolved to lose weight easily. Hunger and fatigue are both adaptations to stop you doing that. And, even if you can shift (1) enough to lose some weight, (2) puts a limit on how much you can lose. Balance is restored by the fact that your lighter body takes less energy to maintain and move around.

The crucial thing is to find some change for which you have both the willpower to adopt it initially and the willingness to maintain it indefinitely. For me, as I said, that’s been exercise. I aim to burn 4000 kj (about 1000 calories) a day in addition to base metabolism, which implies about 100 minutes of vigorous aerobic exercise. That’s logistically feasible for someone with flexible working hours and no kids at home, but very difficult otherwise. And it takes a long while to get to the point where you really enjoy it. That’s why the experts mostly recommend working on diet. But, if you can manage it, I think exercise is the better way to go.

Masks

Now that the World Health Organization has finally endorsed a recommendation for wearing masks in public, it’s time for Australia to do the same.

The most important case is that of public transport including air travel. Urban public transport is vital, but until we take the necessary steps on masks, we will be stuck with recommendations to avoid peak hour travel, guaranteeing a return to private cars and congestions

The airlines have been the biggest transporters of the pandemic and have continued to behave irresponsibly, packing planes as full as possible without any requirement for masks. It’s time for government to step in and order them to require masks as a condition of travel.

Update: I checked and Rex is doing the right thing here, upsetting some passengers who want to be free to infect fellow passengers https://www.abc.net.au/news/2020-06-03/regional-express-passengers-upset-forced-wear-face-covid19/12312358

Fundraiser for MS

I haven’t done a fundraiser for a while, but this seems like a good time. Like everything, the Brissie to the Bay cycle fundraiser for Multiple Sclerosis isn’t going ahead as usual. It’s been replaced with a challenge where participants record their own efforts and set targets for distance and fundraising. I aim to cycle at least 400km in June (my average is around 200), and raise $1000 or more in the process.

Feel free to suggest challenges of your own, with a donation to back them. For example, if anyone is willing to stump up $100, I’ll cycle around Mt Coot-Tha in Brisbane (only 10km, but very tough).

You can donate here and also sign up yourself if interested.

Fundraiser for MS

I haven’t done a fundraiser for a while, but this seems like a good time. Like everything, the Brissie to the Bay cycle fundraiser for Multiple Sclerosis isn’t going ahead as usual. It’s been replaced with a challenge where participants record their own efforts and set targets for distance and fundraising. I aim to cycle at least 400km in June (my average is around 200), and raise $1000 or more in the process.

Feel free to suggest challenges of your own, with a donation to back them. For example, if anyone is willing to stump up $100, I’ll cycle around Mt Coot-Tha in Brisbane (only 10km, but very tough).

You can donate here and also sign up yourself if interested.

Pedestrians and pandemics

A couple of days ago, Adam Creighton had a piece in the Oz, downplaying the risks of the coronavirus pandemic, under the headline “Under 60, in good health? Crossing the road is more risky” Authors don’t choose headlines, but in this case, it’s an exact quote from the article.

There was no supporting analysis, so I decided to do the numbers myself. I looked at Sweden (quoted as a success by Creighton) which seems reasonably comparable to Australia, except that they haven’t gone for a lockdown. I started with some rough estimates on Twitter, and corrected them in response to comments. What follows is the final version.

In 2019, Australia had 172 pedestrian deaths a figure that has been stable for some years. As with the virus, over-60s are more at risk, accounting for 40 per cent of fatalities, compared to 15 per cent of the population. So, just over 100 pedestrians under 60 died last year in Australia. That’s about 2 per week.

Looking at Sweden, there have been 86 virus-related deaths of people under 60 so far, virtually all of them in the last three weeks. That’s about 28 per week, or 14 times the Australian rate

Now we need to adjust for the population difference. Sweden has about 10 million people and Australia about 25 million (ideally, we’d look at the under 60 population, but I’ll leave that adjustment for later). So, as of now, the virus risk to Swedes under 60 is approximately 35 times as great as the risk to Australian pedestrians under 60.

We don’t know how things will change in Sweden. Their strategy is one of “flattening the curve” while allowing the virus to spread slowly. Unless (as some have claimed) there are a huge number of undetected case, it will take a long time to reach herd immunity. Perhaps the current restrictions are sufficient to keep R below 1, but that seems unlikely to me. Even if it turns out that way, thousands more will die before the infection fizzles out.

Read More »

Noises off

A couple of weeks ago, I recorded a video presentation about the likely employment effects in Australia, as part of my university’s response to the pandemic. The sound quality wasn’t great, what with reliance on my computer microphone, a spotty Internet connection and my accent, which is too strong even for some Aussies.

The communications people at the Uni got back to me and said it might have to have subtitles, but they could improve things by lowering the volume of the background music. My immediate reaction was unprintable, and while I managed to calm down, I wrote back to say that under no circumstances would I accept any kind of musical accompaniment. They cut out the music and managed to get it done with closed captions (the kind that are turned off my default).

But, obviously, I’m in an aging and shrinking minority here. David Attenborough’s documentaries, which I used to love, are now unwatchable (or rather unlistenable), with lush orchestral music crashing over his narration. If it’s not that, it’s an annoying metronomic repetition of the same five notes over and over. When people complain, the answer is “this isn’t a lecture”. But that’s exactly what I want from a documentary – a lecture with high-quality video combining to convey more information than either alone. Music, by contrast, conveys no information at all (except, I guess, “this is bad music”). If I wanted a content-free audiovisual experience, I’d far prefer a live band at the pub, with smoke and strobe lights, to someone’s musical interpretation of animal behavior overlaid on some barely audible talk.

Thinking about this brings up the more general issue of background music in films. It’s such an established convention you barely notice it most of the time. But I’ve quite often had the experience of hearing vaguely dissonant music as a character enters a room, and not knowing if this is part of the film, supposed to be audible to the character, or just part of the soundtrack. It’s just as artificial in its way as the characters in a musical bursting into song at the drop of a hat, and yet it’s a standard part of what is supposed to be realistic drama.

That’s it from my Grumpy Old Guy persona. Does anyone share my grumpiness, or want to persuade me out of it.

Unlocking

Lockdowns work. That’s the evidence from many different countries now, including Australia. To be more precise, lockdowns reduce the effective reproductive rate of the virus to the point where it is below 1, meaning that, on average, each infected person passes the disease on to less than one other person. As long as this is sustained, the number of new cases will keep declining, as we have now seen. Potentially, as has been claimed to be the case in China, it will reach zero.

Although some people are still talking about “flattening the curve”, it now seems clear that the best strategy is (near) eradication, pushing the number of infections down to (or near) zero, and preventing any resurgence. But what comes next?

Read More »

Keeping one day ahead of the curve

As soon as the government released its modelling of the pandemic a few days ago, I realised something was badly wrong. The modelling showed infections increasing even under lockdowns, which obviously wasn’t happening. The crucial parameter here is R, the number of new infections generated by each existing infection. If R is greater than 1, the number of infections grows exponentially, but if R is less than one, it declines, eventually approaching zero. The knife-edge case is R=1, when the number stays constant.

On checking the paper on which the modelling was based, I found that it did indeed assume R>1, even with social distancing. This was less surprising when I realized it was based primarily on data from the initial outbreak in Wuhan, before the lockdown in China had taken full effect. (I later discovered that the report had been given to the government in February, which makes its release now rather pointless).

I quickly drafted an article explaining the importance of R and the fact that the modelling was out of date. I thought it would attract plenty of interest, but in fact it was very difficult to place. A lot of editors were unwilling to challenge the government on this. I eventually managed to get it run in Inside Story.

My time outside the tent didn’t last long. Today, the Deputy CMO Paul Kelly gave an analysis that matched mine almost exactly, and effectively abandoned the “flattening the curve” strategy in favour of eradication. The only difference is that he thinks R is “on the cusp of” falling below 1, while I think it’s already there. Some conservativism is called for here.

This has been the whole story of the pandemic for me. Almost every time I’ve criticised the government for not doing or saying something, they’ve got it right (or nearly right) a day or two later. Compared to my usual experience of waiting years for any kind of vindication of my argumetns on policy, it’s a strange feeling.

What next ?

I’ve had my say on the election, and don’t intend to engage in post-mortems. The only question of interest for me now is: what to do next?

I can’t see any useful contribution I can make to Australian politics for the moment, though I’m happy to take suggestions. Serious policy development is going to be off the agenda for some time, and I’ve got nothing new to say about political strategy or day-to-day politics.

‘But the big issues I’m interested in (climate change, and the choice between socialist and Trumpist futures) are global and long-term. I’m going to spend some time thinking and writing about them. I want to put forward some possible visions for the long term (2050 or 2100) future, while maintaining urgency about the threats we face right now.