A “layer” (a chicken that lays eggs) eats about 110 g of chicken feed per day.
Assuming that chicken feed has a metabolizable energy content of 3.3 kWh
per kg, that’s a power consumption of 0.4 kWh per day per chicken. Layers
yield on average 290 eggs per year. So eating two eggs a day requires a
power of 1 kWh per day. Each egg itself contains 80 kcal, which is about
0.1 kWh. So from an energy point of view, egg production is 20% efficient.

The energy cost of eating meat

Let’s say an enthusiastic meat-eater eats about half a pound a day (227 g).
(This is the average meat consumption of Americans.) To work out the
power required to maintain the meat-eater’s animals as they mature and
wait for the chop, we need to know for how long the animals are around,
consuming energy. Chicken, pork, or beef?

Chicken, sir? Every chicken you eat was clucking around being a
chicken for roughly 50 days. So the steady consumption of half a pound a
day of chicken requires about 25 pounds of chicken to be alive, preparing
to be eaten. And those 25 pounds of chicken consume energy.

Pork, madam? Pigs are around for longer – maybe 400 days from birth
to bacon – so the steady consumption of half a pound a day of pork re-
quires about 200 pounds of pork to be alive, preparing to be eaten.

Cow? Beef production involves the longest lead times. It takes about
1000 days of cow-time to create a steak. So the steady consumption of
half a pound a day of beef requires about 500 pounds of beef to be alive,
preparing to be eaten.

To condense all these ideas down to a single number, let’s assume you
eat half a pound (227 g) per day of meat, made up of equal quantities of
chicken, pork, and beef. This meat habit requires the perpetual sustenance
of 8 pounds of chicken meat, 70 pounds of pork meat, and 170 pounds
of cow meat. That’s a total of 110 kg of meat, or 170 kg of animal (since
about two thirds of the animal gets turned into meat). And if the 170 kg
of animal has similar power requirements to a human (whose 65 kg burns
3 kWh/d) then the power required to fuel the meat habit is

170kg × 3 kWh/d 8 kWh/d
65 kg

I’ve again taken the physiological liberty of assuming “animals are like
humans;” a more accurate estimate of the energy to make chicken is in
this chapter’s endnotes. No matter, I only want a ballpark estimate, and
here it is. The power required to make the food for a typical consumer of
vegetables, dairy, eggs, and meat is 1.5 + 1.5 + 1 + 8 = 12 kWh per day.
(The daily calorific balance of this rough diet is 1.5 kWh from vegetables;

Figure 13.4. Two eggs per day.
Figure 13.5. Eating meat requires extra power because we have to feed the queue of animals lining up to be eaten by the human.