A thoughtful glance at our modern food preferences suggests we’ve forgotten much of what the whitetail deer knows about sustainable food systems. My goal in this essay is to start us on a path of remembering, so that we can build an energetically sustainable food system that can feed and nourish us far into the future. We’re far from this ideal today.
A whitetail deer’s diet changes over the course of a year to reflect changes in the abundance of its foods. Deer seek out particular calorie-dense foods to maximize energy intake – high fat nuts like acorns, tree fruit like apples, and seed crops like corn and soya – and also attempt to minimize their energy expenditures as best they can. These elements, energy intake and energy expenditure, can be combined to define the concept of energy balance:
Energy balance, sometimes referred to as energy ratio, energy return on energy invested or simply energy return, drives the ability of an organism to survive and reproduce, assuming it can avoid its predators. In the biological realm as in the physical realm, energy is the underlying constraint that limits all processes. A whitetail, for example, will burn 2,500 Calories in a day (its daily energy expenditure) and eat 4,480 Calories (about 2 pounds) of acorns. Dividing intake by expenditure yields an energy balance for the day of about 1.8, meaning the deer gets 1.8 units of energy for a 1 unit investment. As long as the deer gets back more than it invests (remains in energy-positive territory), it’s doing well, energetically.
In estimating an organism’s energy balance, particularly if that organism uses tools to help it acquire food, three types of energy expenditures are accounted for: labor, fuels, and embodied energy. Labor includes metabolic energy (basal metabolism and additional work to acquire food above this), while fuels include materials burned or otherwise consumed to power machinery or provide heat, such as gasoline, diesel, propane or wood. Embodied energy includes the energy used to build and maintain tools, including machinery, buildings, roads and other things. Estimating the embodied energy costs of a combine, for instance, entails estimating the energy required to mine the metal ores, smelt them into metal, fashion and assemble the combine parts, transport the finished combine from the factory to the farmer’s barn and finally maintain that combine year after year. The energy of labor and fuels are comparatively easy to estimate in an industrial food system, while estimating embodied energy is, at best, an inexact science.
Like the whitetail, ancient people strove to maximize their energy intake and minimize their energy expenditures. Estimating their energy balance is challenging since they didn’t leave records of their diets and the energy expenditures needed to procure them, but studies of extant tribal societies show that their food systems can generate sizable energy surpluses. This is particularly intriguing since some of the tribes, such as the African bushmen, live in marginal desert environments where one would expect food to be scarce. If the food systems of people living in these marginal environments can achieve a positive energy balance, developed societies with industrial-scaled food systems should achieve even higher energy balances, right?
Does our food system deliver a positive energy balance?
It does. Sort of.
People in developed countries have access to many more calories each day than they burn in pursuit of those calories. The average American, for instance, eats about 2,000 Calories per day, but only a tiny proportion of a person’s daily metabolic energy expenditure is devoted to acquiring food. Americans appear to enjoy a lavishly energy-positive diet.
While the average American does enjoy a positive energy balance with respect to human labor, our food system isn’t energy-positive if we consider energy inputs beyond human labor. The United States Department of Agriculture estimates that to deliver the average American’s 2,000 Calorie diet requires nearly 32,000 Calories of energy inputs. Whereas the whitetail invests one calorie of energy to forage and digest its acorn meal and gets back 1.8, we invest 15 calories of energy into our industrial food system and only get back one. Industrial fuels and the embodied energy in machinery and other tools dwarf human labor as energy costs in the US food system, and their magnitude is so great that, when they’re considered, the US food system operates at a steep energy deficit.
In fact, the USDA calculations portray an overly optimistic picture of the US food system because they don’t include all energy costs. They don’t account for the energy costs of disposing of waste food and its packaging, the energy costs of wastewater treatment associated with food consumption or the embodied energy of food-related products and materials imported from other countries. Other researchers who attempt more expansive analyses of the US food system estimate that Americans might invest as much as 20 calories into their food system to get back one as edible food. For all our self-aggrandizing thoughts about modern technology and industrial efficiency, our food system’s ability to deliver nutritional calories at a positive energy balance falls far short of that of the ‘primitive’ African bushman, or even the humble and ubiquitous whitetail deer.
Why haven’t we starved?
The answer is pretty straightforward: subsidies. But I’m not talking about the subsidies written into the Farm Bill, the cash that flows to farmers from federal and state governments for producing commodity crops. I’m talking about energy subsidies of the kind that allow us to sink 15-20 calories of energy into our food system and persist year after year even as we get only one calorie back as edible food.
Whereas the whitetail deer and even the African bushman operate on solar-powered food systems, our industrial food system depends on stocks of ancient sunlight in the form of oil and natural gas to run. Oil, a liquid mineral extracted from beneath the Earth’s surface, is refined to make diesel, gasoline and other energy-dense liquid fuels that power machinery, and is also a feedstock used by the chemical industry to produce pesticides and other chemicals. Natural gas, extracted similarly to oil, is used in the Haber-Bosch process to make nitrogen fertilizers, without which yields of most crops would plummet. Natural gas is also used as a feedstock to make other agricultural chemicals, and as a fuel to provide heat and electricity.
Oil and natural gas are subsurface stockpiles of ancient sunlight. These stockpiles began their ‘lives’ as microscopic plants and animals growing in ancient, shallow lakes and seas at a time in Earth’s history – hundreds of millions of years ago – when the planet was far warmer than today. The microscopic plants turned sunlight into biomass, and the microscopic animals grazed on them. The prevailing climate allowed these microscopic communities to proliferate, and as organisms died and sank to the bottom they created sediments that were rich in organic material. As layer upon layer of these sediments were buried, subsurface heat and pressure eventually ‘cooked’ the organic material into what we today recognize as oil and natural gas. The process by which these stocks of ancient sunlight formed hasn’t ended; oil and natural gas continue to cook in the Earth’s subsurface although their rate of formation is miniscule relative to the rate at which we currently extract and use them. For all practical purposes, oil and natural gas are finite resources.
Over time, the extraction rate of oil and natural gas will progress through stages of growth, peak and decline, following a roughly bell-shaped curve. An investigation of global oil and North American natural gas markets suggests their peaks might not be far off, with recent price volatility and a reliance on debilitating extraction methods like hydraulic fracturing being two of many telling symptoms of emerging scarcity. Oil and natural gas are not substitutable. If a global peak in oil supply emerges, the high prices of key fuels like diesel and gasoline will cut into food production like a knife by diminishing profitability at all levels of our food system and forcing consumers to pay much higher prices. The same would occur if a natural gas peak were to emerge, albeit by way of the cost of fertilizers and other chemical inputs.
The fossil fuel-powered productivity revolution in agriculture that has so reliably delivered an abundance of cheap food for decades was a progress trap. These ‘advances’ delivered more and more food to growing numbers of people, but they also drove our food system into a deep energy deficit, one that can’t be escaped by the application of more energy-intensive technologies. While this energy deficit won’t cause immanent starvation, it doesn’t bode well for the long- or even moderate-term viability or resilience of our food system should energy constraints or economic uncertainty emerge. At some point we must reconsider the design and implementation of our food system on a very fundamental level, and the sooner we begin, the better off we’ll be.
Towards an energy-positive food system
The 21st Century will be a century of challenges. Because acquiring food is such a fundamental physiological need for the human species, adapting our food system to meet our needs without yielding an energy deficit will be foremost among these challenges, and the climate destabilization emerging around the globe won’t make this adaptation any easier. To shift our industrial food system from its energy deficit to being even marginally energy-positive will require a radical re-envisioning of not only how we produce food, but also, most likely, what we eat. Rather than lay out a series of suggestions and their associated energy savings, I think a more valuable approach is to offer a series of questions for readers to consider.
First, the USDA estimates that just the agricultural segment of the US food system requires over 2 calories of energy to deliver one calorie of edible food, already a steep energy deficit. Might we have something to learn from the many indigenous peoples who used low-energy practices to maintain diverse, highly productive landscapes from which they gathered food rather than relying on industrial monocultures? Could the future of our food system revolve around using foods that don’t require of us such intensive mechanical, chemical and labor inputs? What would happen if we integrated the rearing of livestock and the growing of plant foods on a single piece of land to reduce the need for externally-supplied fertilizers and to enhance the diversity of uses to which land can be applied? What if we designed our agricultural systems and perhaps food systems more generally so as to abolish the very idea of waste, requiring that all outputs serve as valuable inputs for other stages in the food production cycle?
While there are plenty of energy savings to realize in agriculture, this element of our food system represents a small proportion of total food system energy demand. Value-added stages – processing & packaging, wholesale & retail, and the food service sector – are comparative energy hogs. Nearly 4 calories are invested in processing and packaging per calorie of edible food eaten, illustrating how energetically expensive our preferences for processed food are. What if we focused on eating whole foods that didn’t require processing or packaging? The wholesale and retail segments of our food system are also energy-intensive, demanding nearly 2.5 calories of energy to deliver a calorie of edible food, while the food services sector – restaurants, catering, etc. – tallies up nearly 3 more calories per calorie of consumed food. What would be the impact of reducing our reliance on these sectors, of buying directly from farmers, of growing our own food? What would be the energetic impacts of preparing our own foods rather than patronizing the food service sectors?
Freight requires over 1,000 Calories worth of energy to deliver the average American’s daily food intake, and relying on local motorized transport to deliver food can actually increase transportation energy use per delivered calorie of food over that of national freight because local delivery systems move smaller amounts of food per unit fuel consumed. How ‘local’ does a local food system need to be to become energy-positive?
Finally, household energy use makes up the single largest share of food system energy expenditures, currently accounting for over 4 calories of energy invested per calorie of food eaten, which includes the energy costs of refrigeration, freezing, cooking and appliance use. What whole food recipes that rely on energy-dense foods and that don’t require much in-home preparation can we rediscover to enhance our food system energy balance? What foods can we eat that don’t require energy-intensive storage methods like refrigeration and freezing, and what less energy intensive food storage technologies are available for us to rediscover?
As food consumers we also need to step back and ponder another driver of food energy demand – our diets. We eat particular foods for various reasons, sometimes because we were raised on them, sometimes because we succumb to food producers’ marketing ploys, and sometimes we adopt a set of preferences to achieve a coveted health outcome, or at least avoid a negative one. The health food community is overrun by diet fads, and most of these completely miss the point of food: to deliver sustenance at a positive energy balance. Precisely which foods offer the highest energy balances will vary geographically because an input intensive food in one region might be much less input intensive elsewhere. A few questions we need to ask ourselves with respect to our diets are: What local foods can be produced in my area using very low inputs? What foods can be eaten with minimum processing? What foods can be stored without refrigeration or freezing? These questions are admittedly just the tip of the iceberg, but they’re a good start.
To prove that energy-positive foods do exist in the modern developed world, take this example of a recipe for lacto-fermented burdock root that I make every August. The recipe is simple: I walk to an area (my backyard, for instance) where burdock grows without any help from me. I dig up the roots – which can be over 20 inches long and sometimes thicker than my wrist – then wash, peel and chop them. I dust the chopped roots with sea salt so they create their own brine, and pack them in mason jars to ferment for a few weeks. I avoid cooking the burdock partly because cooking is very energy intensive and forces most foods into energy-negative territory, but also because fermenting makes many foods taste better to me than cooking does. The recipe delivers 1,600 Calories of edible food and requires 800 Calories of metabolic energy expenditure (including basal metabolism and labor) as well as about 350 Calories of embodied energy in the mason jars, the sea salt, various tools and the water used to wash the roots and clean up afterwards. Overall the recipe has an energy balance of 1.4 and delivers an energy surplus of about 440 Calories. I chose this burdock recipe to show that it is possible to deliver an energy-positive food even with a vegetable that isn’t particularly energy dense provided one chooses processing methods and operational scales wisely. As more people begin studying recipes through an energy lens, a wide range of nourishing foods that deliver an energy surplus will surely emerge.
My ability to deliver a recipe that yields a positive energy balance depends on many things, including learning what minimum-input foods are available in my area at this time of year as well as knowing techniques, like lacto-fermentation, that allow me to turn marginally edible foods into palatable, nutrient dense foods without huge energy investments. Another important issue – one that is too often overlooked, in my opinion – is operational scale. In most production systems the benefits of increasing scale are subject to diminishing returns, and this is particularly true for the relationship between scale and energy balance. As scale first begins to increase – from not processing anything at all, to processing a single burdock root, to processing 10 of them – efficiencies of scale emerge that increase the energy surplus a particular food can offer by reducing the per-calorie energy input requirements. These reduced input requirements might take the form of reduced metabolic energy costs per unit of finished product, or reduced embodied energy costs due to spreading the embodied energy of tools or other inputs over a disproportionately larger amount of finished product. Efficiencies of scale are incredibly valuable in food production, and their judicious application is paramount to staying energy-positive.
But efficiencies of scale have their limits. All operations – including food production operations – reach a point at which further scale increases no longer deliver energy savings and in fact they deliver disproportionate energy costs. At this transition point, shown as a peak in energy balance in the graph above, continued increases in scale actually eat into the overall energy surplus, making the operation more and more marginal. At some point scale increases until total energy inputs equal the energy returned, and we find ourselves at the point where the operation’s energy balance falls to the break-even point of 1, illustrated above by the red horizontal line. Any further increases in scale force the operation into energy-negative territory, shown above with red shading beneath the energy balance curve.
Declining marginal returns might emerge for many reasons in food systems. Perhaps operational scale rose to the point that mechanization was required and either the needed fuels or the embodied energy in machinery killed the energy balance. Perhaps the operational scale increased to the point that local markets were saturated with the product and motorized transport became necessary to ship it to distant markets. Perhaps consumers got bored with simple recipes using the product, and started using more energy-intensive methods of preparation like cooking or attempted to store it using refrigeration or freezing. Regardless, what was once an energy-positive food product goes energy-negative, and if too many individual food products follow this path the entire food system will fall into energy-negative territory.
In the US food system, operational scale has increased far beyond the point of declining returns as evidenced by the fact it yields a steep energy deficit. Our task now is to reduce the operational scale of our food system and search for that sweet spot that maximizes energy balance. By this I don’t mean we need to produce less food, but rather we need to reorganize our food system so that the unit of land management and food production shrinks, backtracking along the above graph until operational scale eases back into energy-positive territory.
Food activism of all sorts –centered on the availability of un-pasteurized dairy products, meat butchered on the farm where it was raised, and direct-to-consumer sales of products that currently require inspection or certification – is rising up throughout American society like a wellspring. This wellspring is creating an enormous opportunity, both to create new food products and markets, but also to ask deep, profound questions about our food system’s development and whether its path is a viable one over the long term. What good is a food system, after all, if its high energy intensity eventually sends the nation spiraling into both nutritional and energetic poverty?
Food plays many vital roles in modern life, not only sustaining human lives by feeding us but also by providing jobs, entrepreneurial opportunities and aesthetic value. Many values are wrapped up in our food choices, and perhaps its time to put those values on the table. I hope the analyses I’ve offered and the questions I’ve left unanswered spark discussion, over the dinner table, at farmer’s markets and perhaps even at City Council meetings, and I hope they drive us towards a resilient, energy-positive food system. Or, at the very least, I hope they offer some rich food for thought.
I thank Kenneth Mulder (Green Mountain College), Michael Bomford (Kentucky State University), Connor Stedman (University of Vermont) and Alison Nihart (University of Vermont) for offering valuable editorial and technical comments on this essay.
- Acorns contain about 140 Calories per ounce.
- ‘Energy return on invested: towards a consistent framework’ (Mulder & Hagens, Ambio, 2008)
- The term ‘calorie’ is somewhat ambiguous. Physicists use the term calorie (with a small ‘c’) as a measure of heat. Nutritionists use the term Calorie (with a capital ‘C’) in the same way, but the two are not equivalent. A nutritionist’s Calorie equals 1,000 of the physicist’s calories, hence nutritional calories are often called kilocalories (kilo- is the metric prefix for 1,000).
- Man the Hunter (Lee & DeVore, 1968), Stone Age Economics (Sahlins. 1972)
- Energy Use in the U.S. Food System (Canning et al., 2010)
- Food, Energy and Society (Pimentel & Pimentel, 2008)
- Electricity from coal, a fossil fuel, nuclear power and other sources is also important, but their contribution is small compared to oil and natural gas and is more substitutable.
- Although oil and natural gas are the main energy subsidies, topsoil, groundwater and biodiversity are also being depleted in pursuit of industrially produced food.
- ‘Energy from fossil fuels’ (Hubbert, Science, 1949)
- See the essay Energy, Economy and the Impending Rite of Passage at http://www.Path2Resilience.com.
- A Brief History of Progress (Wright, 2004)
- Tending the Wild, (Anderson, 2006)
- ‘Benefits of re-integrating livestock and forages in crop production systems’ (Clark, Journal of Crop Improvement, 2004)
- Cradle to Cradle (McDonough & Braungart, 2002); The Humanure Handbook (Jenkins, 2005)
- ‘Food-miles and the relative climate impacts of food choices in the United States’ (Weber et al., Environmental Science & Technology, 2008); energy costs of food transport are closely correlated with the greenhouse gas emissions tallied in this study.
- Wild Fermentation, The Art of Fermentation (Katz, 2003, 2012)
- I gather 5 pounds of wild burdock, with a calorie density of 20 kcal per ounce. I estimate gathering and processing would require about 4 hours of work, which entails about 400 Calories worth of basal metabolic output as well as another 400 Calories of labor. I estimate that each jar’s embodied energy is about 50 Calories, which assumes I’ll reuse each jar 20 times before it breaks or gets recycled. I estimate the embodied energy of my trowel as 20 Calories, which assumes a total embodied energy of 5,000 Calories and that I’ll use it about 250 times before it breaks and needs to be replaced (I suspect it will last much longer, but I want to be conservative here). I estimate the embodied energy of my chef’s knife to be 20 Calories, which assumes a total embodied energy of 10,000 Calories and that I’ll use it about 500 times before it needs to be replaced (I suspect it will last much longer). I assume tap water to have an embodied energy of 1,100 Calories per cubic meter, and I use about 0.38 cubic meters (10 gallons) to wash the burdock roots and clean up after processing. I assume that sea salt has an embodied energy of 90 Calories per kg, and I use about 0.1 kg to salt the chopped roots. All energy values were derived from Food, Energy and Society(Pimentel & Pimentel, 2008).
- See Figure 4 in Mulder & Hagens (2008), cited above.