Food provides people with energy, but it also takes energy to gather, cultivate, process and prepare food. The difference between the energy consumed as food and the energy used to produce it, is the net energy of food production. Most food in modern economies has negative net energy, meaning most food takes more anergy to produce than it provides. This is unsustainable.

If a human uses more calories than he ingests (i.e. negative net energy) he will die quite quickly. In survival situations it is advised that you stay put and conserve as much energy as possible. It is counterproductive to hunt or forage for food when it’s likely that the calories you use is more than you gain.

Before the industrial revolution, and the widespread use of fossil fuels, the energy for agricultural production came from people and from ‘beasts of burden’. If a farmer can only produce enough food for himself, his family and his animals, with perhaps a little left over to trade for clothes and other essential goods, it is called subsistence farming. This is the type of farming that occurs in many poor parts of the world today.

If, through good circumstances, a farmer can produce a surplus to his requirements, he can feed more than one family. This means that some people can do other things than growing food, which leads to a division of labour. In history, it was this division of labour that ultimately led to the development of complex civilisations.

It should be remembered that food grows naturally without any human intervention. All food is a natural product of biological processes, including the ‘capture’ of nutrients from the air and the ground as well as energy from the sun. However, early humans realised that they could intervene in these natural processes and cultivate certain plants and animals to secure and increase yields. From that time agriculture has become increasingly mechanised and industrialised, especially in past 150 years.

Industrial agriculture is heavily reliant on fossil fuels, for fertiliser and pesticides, as well as for cultivating, processing and transportation. A string of combine harvesters can do the work of hundreds of people with scythes, and in a fraction of the time. What this means is that in America today it takes 10 calories of fossil-fuel energy to produce one calorie of food energy.

Not all foods are equal. Grains, specifically wheat and corn, have a high calorific value relative to the amount of calories it takes to farm them. Grain-fed beef on the other hand has a very low calorific value compared to the energy expended in producing it.

The table below shows the net energy of a variety of foods. This correlates to the size of the carbon footprint of different foods, since most of the energy expended comes from burning fossil fuels.

The picture is complex but, relatively at least, industrial farming is not sustainable, meaning the volume of meat, in particular, currently consumed must decrease.

Energy Efficiency of Various Foods

(Measured as Food Calories / Energy Used in Production)

Food Calories / Lb  Energy Efficiency
Corn 390 102%
Milk 291 45%
Cheese 1824 31%
Eggs 650 19%
Apples 216 15%
Chicken 573 15%
Pork 480 8.5%
Beef 1176  4.3%

Source: http://www.theoildrum.com/node/6252

Just as all foods are not equal, neither are all farming methods. The figures above are estimates for industrial scale-farming, including factory farming of beef, pork and chicken. Small-scale, intensive, organic farming uses considerably less fossil fuel inputs than large-scale industrial farming. Grass fed beef has a higher energy efficiency than grain-fed beef and organic grass-fed beef has an even higher energy efficiency still.

In a lower-energy future it is highly unlikely that people will go back to subsistence farming. However it is likely we will go back to farming a little like it was done in the early 1900s. Smaller scale farms, more hands-on with the help of horses, mules and oxen. There will be much less use of herbicides and pesticides, farming will be organic, for the simple reason it will have to be, as fossil fuels become more expensive and eventually run out.

Instead of waiting for that day to come, which might be too late, we should be moving to smaller-scale, low-energy-input, organic agriculture now.