# A Physics-Based Diet Plan

The 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.

# Flex-Fuel Humans

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.

# Heat those Feet!

Infrared image of a cold left foot (25°C with 19°C toes), compared to a warm (33°C) right foot.

One of the more bothersome aspects of living in an unheated house (with tile floors in much of the house, in my case) is having cold feet. Spring has arrived, so perhaps this post is not as timely as it might otherwise have been. But let’s consider the energy costs of various approaches to warming up cold feet.

The main problem I have with cold feet is that they make it hard to go to sleep. Otherwise cold feet don’t seem to distract me from normal activities. But let’s say that your feet are cold and that you cannot stand it any longer, and therefore must warm them up. I’ll look at a number of options, assessing how much energy is consumed for each. We’ll try hot water in the sink, a space heater (or blow dryer) under a blanket, a heating pad wrapped around the feet, or good-old metabolic energy.

# 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.

# The Biofuel Grind

When we enter the decline phase of conventional oil—likely before 2020—we will scramble to fill the gap with alternative liquid fuels. The Hirsch Report of 2005, commissioned by the U.S. Department of Energy, took a hard look at alternatives that could respond to the scale of the problem in time to have an impact. Not one of the approaches deemed to be currently viable in the report departs from fossil fuels. But what about biofuels? To what extent can they solve our problem? We’ll dip our toes into the math and see where a first-cut analysis leaves us.

# Garbage In, Garbage Out

How many times have you heard it: if we could tap into the energy embedded in our copious waste streams, we could usher in a new era of energy independence—freeing ourselves of the need to support oppressive regimes who happen to sit atop the bulk of the oil reserves in the world. In fact, these sorts of claims are abundant enough to give the impression that we have a cornucopia of fresh (and sometimes not so fresh) energy solutions to pursue if we got really serious. This is a hasty and dangerous conclusion, so in this case, waste makes haste.

I consider this perceived abundance of technological solutions to be one of our worst enemies in developing sensible solutions to the coming fossil fuel energy crunch. If ideas abound, each claiming some ability to free us of foreign oil, then surely we’ve got the situation under control and don’t need to invest substantial time and energy today to solve what looks like a non-problem of tomorrow. But what if the claims are overblown, hyped, or just plain wrong? At best, this is irresponsible behavior. At worst, the resulting sense of complacency could delay substantive action to our ruin. Continue reading