I was able to start riding my bicycle again, this past week, after more than a year of being unable to do so. That got me to thinking about how personal transportation has turned topsy-turvy in the 25 years that I’ve been pedaling this same semi-recumbent bike.
Source: Prius: fueleconomy.gov. bikeE: bicycleman.com
1 Do you believe in the laws of physics? Then you understand that food fuels bicycles.
That’s a serious question.
Nuclear reactions aside, do you believe in the law of conservation of energy? That’s the basic physical law that holds that energy is neither created nor destroyed, but is merely converted from one form into another.
You should. Because everybody who’s ever tried to test it has found that it’s true. (Aside from nuclear reactions that convert mass into energy.) This law is the reason that perpetual motion machines that do useful work are impossible, and why various types of “free energy” machines — machines that produce more energy than they consume — are likewise impossible.
Let me assume that you are a believer. (You have no business reading this blog if you aren’t.)
And so, intellectually, you realize that the energy to propel a bicycle has to come from somewhere.
You will eventually realize that bicycles are powered by an extremely highly refined form of fuel that we call “food”. If not directly, then from energy stored in the body that itself, ultimately, came from food. If your weight is stable (if you’re not burning up stored fat over time), all the energy to propel your bike comes from the food that you eat.
I need to emphasize that, because that simple fact gets lost on the casual bicyclist. The additional calories consumed, to offset calories burned in bicycling, are typically not explicitly noted or noticed. They get lost amid the daily ebb and flow of the diet.
But if you’ve ever done a lot of bicycling, over a sustained period of time, you will notice yourself fueling up. At one point in my life, I bike-commuted to work, a few days a week, at a bit over 30 miles a day. That’s about 1500 calories a day. And at that level of intensity, yes, I ate noticeably more.
But if you’ve never had that experience — never really used your bike for sustained daily long-distance travel — then “food fuels bikes” really is a matter of belief. If you believe in the law of conservation of energy, then you believe that food fuels bikes, period. Even if you, yourself, have not empirically observed that long-term, long-distance bike riding will result in higher calorie intake, holding body weight constant.
Hence the opening question.
2: How many Calories in a gallon of gasoline?
Makes a surprisingly good apéritif.
OK, I’m kidding about that.
But I’m not kidding about expressing the energy content of a gallon of gasoline in (dietary, kilo-) Calories. A Calorie is simply a unit for measuring energy content. One dietary Calorie (or physicists’ kilocalorie) is roughly equal to four BTUs (British Thermal Units).
Maybe this will make you feel better about it. How many calories in a gallon of vegetable oil? Google puts it around 32,000. That benchmarks well with the commonly-cited 120 calories per tablespoon, and 256 tablespoons per gallon.
But realize that vegetable oil makes excellent motor fuel, if you are driving a diesel (reference).
Gasoline is just a touch less energy-dense, and (depending on the formulation) comes in around 31,000 calories per gallon (reference).
3: How much fossil fuel is require to produce food?
This is one of those slipperier-than-you-might think statistics. Everyone agrees that the U.S. food supply uses a lot of fossil fuels (e.g, reference). But estimates of the average amount required, per edible calorie, vary. That’s due in part to difference in methods (e.g., is in-the-home energy use considered, how are restaurants factored in, is food waste (reference) considered, and so on.) If nothing else, the amount of fossil fuel required varies enormously by the type of food being produced, so your estimate will depend to some degree on the average diet that is assumed.
So I’m going to punt on the details. Just let it be said that you can find both higher estimates and lower estimates than what I’m going to use.
In America, the typical cited value is that it takes 10 fossil-fuel calories to produce one edible calorie (reference, reference).
I should point out that something close to this 10-fossil-fuel calories figure can reasonably be derived from U.S. aggregate data. For example, the USDA estimates that the U.S. spent about 12 quadrillion BTUs of energy on the entire U.S. food chain in 2012 (The Role of Fossil Fuels in the U.S. Food System, USDA Economic Research Report #224). Dividing that by U.S. food consumption (that is, excluding waste) of about 2400 Calories per capita per day, simple long division (and the understanding that a Calorie is about 4 BTUs) gives 9.6 fossil-fuel Calories per edible Calorie. (Calculated as (BTUs of energy / persons x calories per year / 4) = (12 x 10^15 / ((360 x 10^6) x (365 x 2400) / 4 =) ~ 9.6).
Close enough to 10. FWIW, and not shown here, I’ve done the math starting from other U.S. totals and come up with somewhere around 14.5 fossil-fuel Calories per edible Calorie.
What I’m getting at is that, while there is some uncertainty about that number, you can get close to it enough different ways, from enough different sources, that it appears reasonably credible.
For the sake of argument, let’s go with 10 fossil-fuel calories per edible calorie consumed. And ignore all the caveats.
If nothing else, it’s a nice round number.
4: How far can I bike on 3100 calories?
I’m a fairly big (i.e., fat) guy. Based on exercise tables, 3100 calories of food ought to take me about 63 miles on a bike.
The upshot of points 2 and 3 above is that if I eat the typical American diet, then eating 3100 calories of food is roughly equivalent to burning a gallon of gasoline. Both result in the consumption of about 31,000 calories of fossil fuels. The gasoline, directly. The food, indirectly, via the fuels consumed by the U.S. food supply chain.
Putting those two facts together, I get about 63 MPGe on my bicycle. That is, my mileage is roughly equivalent to a car getting 63 MPG. The act of bicycling itself is extremely efficient, compared to driving a car. But production of the fuel that the bicycle uses — food — uses so much fossil fuels that it largely offsets the physical efficiency of bicycling.
I am far from the first one to have put these facts together in this fashion. My eyes were opened years ago by “Bicycling Wastes Gas“.
More recently, I stumbled across the “do the math” blog, where a university professor makes the same point. If that 10-calorie figure is correct, then walking consumes just about as much fossil fuel per mile as driving a typical standard gas sedan (reference).
5: How cars have changed since 1998.
In 1998, I bought a bikeE-brand semi-recumbent bicycle from my local bike shop, bikes@vienna.com. (That’s the bike pictured at the start of this posting.) That bike shop is still thriving. And I’m still riding that bike, thanks entirely to the low stress that a semi-recumbent bike puts on your body.
But my, how the world of cars has changed.
Using the fueleconomy.gov website, I find that in 1998, the highest-gas-mileage new car you could buy got 40 MPG. That was for a three-cylinder, one-liter, 55-horsepower Chevy Metro.
That’s it. In 1998, one new car got 40 MPG or better. Nothing else in the 1998 model year was rated above 40 MPG except for an experimental electric car (lease-only) from Honda.
For the 2023 model year, by contrast, if I require at least 40 MPG (or MPGe), fueleconomy.gov returns 146 vehicles, ranging from 40 to 140 MPG or MPGe.
The upshot is that in 1998, even accounting for the fossil fuels required to produce food, bicycling consumed less fossil fuel per mile than any new car I could then buy.
In 2023, that’s no longer true, and by a wide margin. As noted above, the EPA rates the Prius Prime for 133 MPGe, at 4 miles per KWH. But as we drive (mostly around town), we get an actual average of about 5.5 miles per KWH, which would be about 180 MPGe. The upshot is that a fat guy, bicycling down the road, consumes about three times as much fossil fuels per mile, as that same guy driving a Prius in EV mode. That all assumes that I’m eating the average U.S. diet.
Conclusion: Energy-efficient bicycling is hard to swallow.
The plain fact is that cars have become much more efficient, but bicycling has not, and food has not. And the only way I can increase the fossil-fuel efficiency of my bicycling it by changing what I eat. As different foods, and different food consumption locations, result in the consumption of different amounts of fossil fuels per edible calorie.
I already eat a diet that is far from the U.S. average. For example, the only time I eat fast food is on a road trip. By contrast, for U.S. adults, about 11 percent of total calories come from fast food (CDC, 2007-2013 average). Reportedly, restaurants of all types (including fast food) account for 20% of the calories consumed by the average U.S. adult (reference).
Otherwise, the general gist of a low-fossil-fuel diet is pretty simple: Minimize animal products. You can find lists of fossil-fuel-intensiveness of various foods, and while the details may differ, that’s pretty much the gist of it. Minimize highly processed foods. Virtually all forms of food processing consume energy. Getting food in as close to its original commodity form reduces the energy input. To a lesser extent, maximize foods grown nearby.
When all is said and done, I’m not sure I’m willing to make my diet any more energy-efficient than it is now. In that case, my bicycling fossil-fuel efficiency is about as good as its going to get. Along with all the other aspects of modern life that I’m having a hard time adjusting to, I’m going to have to live with the fact that, as absolutely crazy as it sounds, driving my (wife’s) car on electricity is less environmentally damaging than bicycling.
What a world. What a world.
