Tag Archives: food

the stuff we eat and associated energetics

Atomic Humans

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Some themes appear to exert a magnetic pull on my attention: I keep coming back to them and often feel like I’m on a treadmill. It’s hard to figure out why: why am I compelled to keep these topics alive? A recent insight ties some of it together.

Years ago, I wrote a post called A Physics-based Diet Plan. The premise is that humans do not create or destroy atoms within their bodies, and that the energetics are too minuscule to register measurable mass–energy conversion. As such, a person’s mass change—as measured on a bathroom scale, for instance—from one day to the next is completely captured by the difference of mass inputs and mass outputs. It’s just atoms in and out.

Now, the human body has many channels for mass loss. Bathroom functions, breathing (net carbon/water loss really adds up!), and perspiration being the main mechanisms. Mass gain is almost entirely through our pie-holes. And entry via that channel is almost always facilitated by a hand delivering food to the mouth under the control of a brain. If you want to lose weight, the directive is simple: eat less and breathe more. In other words: diet and exercise. I know: radical, right? Every successful program for weight loss involves essentially this same advice, in various guises. That’s because it’s just atoms in every single case, at the foundational level. But oh boy, you wouldn’t believe the resistance I get to this framing. Let’s talk about that…

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Finite Feeding Frenzy

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Image by ariesjay castillo from Pixabay

You may be aware that our food industry is heavily dependent on fossil fuels, to the point that it takes about 10 kcal of energy input to deliver 1 kcal of consumed food. The enormous energy multiplier is due to extensively mechanized plowing, harvesting, processing, and delivery of food; fossil-fueled fertilization (via methane feedstock); refrigeration and preparation; then of course food waste. In olden times, when all agricultural energy came from muscle power that needed to be fed, the system would collapse (i.e., starve and fail) if energy inputs exceeded energy ingested.

Some have phrased our current practice as “eating fossil fuels,” and in fact a 2006 book by Dale Allen Pfeiffer had this title. So what? More power to us—literally.

The problem, people, is that fossil fuels are finite. We have already consumed a fair fraction (roughly half?) of the accessible allotment. And before concluding that we therefore have a century or so before needing to worry about the consequences, realize that the inflection point happens around the halfway mark, wherein decreasing ease of access tends to result in ever-decreasing output rates in the second-half of the resource. We see this behavior in individual oil fields and in regional (country-scale) aggregations. The low-hanging fruit is taken first, sensibly, so that what’s left is more stubborn.

Because human population has been substantially boosted by fossil fuel input, we have put ourselves into a vulnerable position. What happens when fossil fuels begin to give out on us?

It’s been a while since I did any, you know, math for this blog, as I seem to be living my own worst nightmare and turning into an armchair philosopher (oh the shame). In this post, I return to something closer to math. It’s illustrative rather than quantitative, but helps frame the peril we have put ourselves into in a low-effort sort of way.

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A Physics-Based Diet Plan

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homer-donutThe holiday season is upon us, and for many, this translates into a marked uptick in the consumption of tasty food treats. I’m no different, and can really pack it in on such occasions. For instance, the day after Thanksgiving this year, I stepped on the scale to find myself about 5 pounds (~2 kg) above normal weight. I kicked in my diet plan, and by Monday morning (3 days later) I was back to normal. Resume course. I use a simple formula, backed by physics, that works every single time. The topic is Do-the-Math-relevant for two reasons: it applies quantitative physics to everyday life, and it touches on attitudes relevant to energy/resource conservation.

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Burning Desire for Efficiency

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Ever wonder how efficient it is to heat water? Of course you have! Ever measured it? Whoa, mister, now you’ve gone too far!

I recently devised a laser-phototransistor gauge to monitor my natural gas meter dial—like ya do. As a side benefit, I acquired good data on how much energy goes into various domestic uses of natural gas. Using this, I was able to figure out how much energy it takes to heat water on the stove, cook something in the oven, or heat water for a shower. Together with the knowledge of the heat capacity of water, I can compute heating efficiency from my measurements. What could be more fun? I’ll share the results here, some of which surprised me.

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Flex-Fuel Humans

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[An updated treatment of some of this material appears in Chapter 20 of the Energy and Human Ambitions on a Finite Planet (free) textbook.]

If you’re one of those humans who actually eats food, like I am, then a non-negligible part of your energy allocation goes into food production. As an approximate rule-of-thumb, each kilocalorie ingested by Americans consumes 10 kilocalories of fossil fuel energy to plant, fertilize, harvest, transport, and prepare. The energy investment can easily exceed a person’s household energy usage—as is the case for me. But much like household energy, we control what we stick in our mouths, and can make energy-conscious choices that result in substantial reductions of energy consumption. I now call myself a flexitarian, a term acknowledging that my body is a flex-fuel vehicle, but also that I need not be rigid about my food choices in order to still make a substantial impact on the energy front.

An earlier post on how many miles per gallon a human gets while walking or biking touched on the fact that fossil fuels undergird our food supply. As a result, walking to the grocery store effectively uses as much fossil fuel as would a typical sedan. The lesson is not to walk less, but to change that 10:1 ratio for the better by eating more smartly. Once upon a time, we put less than one kilocalorie of energy into food production per kilocalorie obtained (or else we and our draft animals would have starved to death). So the 10:1 ratio is not at all inescapable, and depends strongly on the foods we choose to eat.

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MPG of a Human

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On Do the Math, three previous posts have focused on transportation efficiency of gasoline cars, electric cars, and on the practicalities of solar-powered cars. What about personal-powered transport—namely, walking and biking? After stuffing myself over Thanksgiving, I am curious to know how potent human fuel can be. How many miles per gallon do we get as our own engines of transportation?

Okay, the “miles” part is straightforward. And we can handle the “per.” But what’s up with the gallon? A gallon of what? Here we have all kinds of options, as humans are flex-fuel machines. But food energy is not much different from fossil fuel energy in terms of energy density.

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