Want to save the US economy? Go on a diet.
That's the message ecologists are trying to get across this week. They say the apparently looming energy crisis could be averted if US residents cut their calorie intake.
David Pimentel of Cornell University and colleagues have drawn on an extensive body of existing studies to highlight the wastage in the US food production chain. To bring their point home, they have estimated how much energy could be saved by making a few relatively simple changes to the way corn is produced.
Their conclusion is that energy demands could easily be halved. That could stave off the prospect of further rises in the costs of fuel, they say.
To do that, however, would require a considerable change in the average US diet. The average American consumes about 3747 kcal per day compared to the 2000 to 2500 kcal per day recommended by the US Food and Drug Administration.
The 3747 kcal per day figure does not include any junk food consumed.
Producing those daily calories uses the equivalent to 2000 litres of oil per person each year. That accounts for about 19% of US total energy use.
Using data from the UN Food and Agriculture Organization, Pimentel estimates that half of the energy used to make food in the US is spent making animal products - meat, dairy and eggs. Farmers must produce crops to feed the animals that eventually provide humans with animal protein.
In 2004, Pimentel estimated 6 kilograms of plant protein are needed to produce 1 kg of high quality animal protein. He calculates that if Americans maintained their 3747 kcals per day, but switched to a vegetarian diet, the fossil fuel energy required to generate that diet would be cut by one third.
Reducing their meat intake is not the only way Americans can cut the nation's energy bill. And Pimentel's other suggested change to US eating habits would have the added benefit of cutting the national health bill as well.
In addition to the 3747 kcals, the average American consumes one third of their calories in junk food and Pimentel and colleagues suggest this could be cut by 80% and the total calorie intake be reduced by 30%. That could drastically cut the amount of energy which goes into feeding Americans, as junk food is typically low in calories, but energetically expensive to produce.
For instance, Pimentel calculates that the equivalent of 2100 kcal go into producing a can of diet soda which contains a maximum of 1 kcal. About 1600 kcal go into producing the aluminium can alone.
Other suggested changes to the food production process range from replacing incandescent bulbs with energy-saving fluorescent ones, to using fewer machines, pesticides and fertilisers, and more human power on farms.
Reducing the distance that food is transported could also cut energy costs: food travels 2400 km on average to its consumer in the US. This requires 1.4 times the energy actually contained in the food. Producing food locally would cut the energy expended transporting it by half.
Pimentel estimates that the amount of energy that goes into packaging foods could be halved as well, as could the amount of energy used by agricultural machines.
If his dietary and production measures were implemented, he says, the US food industry would consume half the energy it does. Whether or not the US is ready for these changes remains to be seen.