Towards an Energy-Positive Food System
It’s not uncommon to find me wandering through fields and forests in search of whitetail deer. I find that first track, and away I go. I study where the whitetail move, where they’re eating, and where they’re bedding down. I find the stubble left from where they’ve nibbled at grasses and forbs, I find scrapes where they’ve dug up truffles or uncovered acorns, and I find the rubs the males leave on the trunks and lower branches of saplings to claim their territory. And if I walk quietly – and if the birds and squirrels don’t squeal on me – I might even see one.
Across large swaths of North America, particularly throughout the United States, whitetail deer are ubiquitous. So ubiquitous, in fact, that many people pay them scarcely any attention despite their size, which is often comparable to ours. Suburbanites might spy deer browsing their shrubs, rural drivers might see them crossing the road at twilight, and hikers might look up from the trail to glimpse their white tail bobbing off into the forest, but otherwise whitetail deer are an invisible part of the American landscape. This is unfortunate. Whitetail deer have much to teach us.
While the whitetail offers many lessons, this essay focuses on the lesson they offer about diet. No, this is not an essay on being vegan or even vegetarian, it’s much deeper than that. A thoughtful glance at our modern food system suggests we’ve forgotten much of what the whitetail 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.
Where to begin?
Bones. Let’s start with bones.
After a hard winter, it’s common to find whitetail bones hidden among spring brush. Coyotes, foxes, birds and rodents pick the bones clean, although the deer didn’t necessarily die at the hands (or claws) of a predator. A hard winter, particularly one with deep snow, forces deer to burn more calories moving around and finding food than normal, and some of them burn through the body fat they stored in fall and die of starvation before the winter ends. Whitetail know that the calories they derive from their food over the course of a year must cover all of their energy costs, including bodily maintenance and digestion, foraging and fleeing predators, and growth and reproduction. If deer can’t eat enough to cover their energy costs, they’ll be thinner at the end of the year than at its start. If that pattern persists for too long or reaches an extreme, I’ll find their bones in spring.
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. The graph below shows a stylized example of a whitetail deer’s energy costs associated with eating acorns. The energy demands of basal metabolism and foraging count as energy expenditures, while the energy value of the consumed acorns represents the energy intake. In this example, energy expenditures amount to 2,500 Calories for the day, while the 2 pounds of acorns eaten amounts to 4,480 kilocalories, for an energy balance of about 1.8 (the deer gets 1.8 units of energy for a 1 unit investment). The energy break-even point is 1, meaning that one unit of energy expenditure yields one unit of energy intake, so a number above 1 illustrates a positive energy balance (I shorten this to energy-positive) and a number below 1 a negative energy balance (energy-negative).
Energy surplus is a useful companion idea to energy balance. One can calculate energy surplus by subtracting the energy expenditure from the energy intake. In the case of the whitetail eating acorns, the energy surplus is just under 2,000 Calories. This surplus energy allows the deer to grow, reproduce, or put on fat to sustain it through the winter when food is scarce. The drive to maximize energy balance and energy surplus helps to define the evolutionary idea of ‘fitness’, and plays a pivotal role in shaping the habits and dietary preferences for all organisms, including us.
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 out 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 4,000 Calories of energy to deliver 2,200 Calories of edible food, itself 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 freely gathered food rather than investing the energy to create and maintain energy-intensive monocultures? Could the future of our food system revolve around using foods that grow or raise themselves rather than relying on mechanical and labor inputs from us? 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 stage of our food system represents a small proportion of total food system energy demand. Value-added stages – processing, packaging, wholesale and retail, and the food service sectors – are comparative energy hogs. What if we focused on eating whole foods that didn’t require processing or packaging, and on sourcing our foods directly from farmers rather than relying on foods from the top of a long supply chain? On the topic of transport, although it makes up a small proportion of total food system energy use, its magnitude is still huge, requiring over 1,000 Calories worth of energy to deliver the average American’s daily food intake. While re-localization is often offered as a means to reduce transport energy in food systems, relying on local and regional motorized transport to deliver food products can actually increase transportation energy use per delivered calorie of food because they 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, incorporating 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 shift to 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. A life-cycle energy assessment of this recipe shows the modest energy surplus it offers despite including the embodied energy costs of the mason jars, the sea salt, various tools and the water used to wash the roots and clean up afterwards. 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 their processing method and operational scale 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 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. Scale also matters. 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 processing a single burdock root to processing five pounds – energy economies of scale emerge that increase the energy surplus a particular food can offer. As operational scale increases to the point that mechanization is needed to keep up with production or transportation is needed to send products to distant markets because local markets are saturated, then energy consumption rises faster than the energy savings from increasing economies of scale and the overall energy balance of the food product falls. At some point scale increases to the point where total energy inputs rise above the energy returned, and the energy surplus becomes an energy deficit.
In industrial agriculture, operational scale has increased far beyond the point of diminishing 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 agricultural system so that the unit of land management shrinks. Most likely this sweet spot will feature a far reduced degree of mechanization and the fruits of the land will serve hyper-local markets to avoid the need for motorized transport.
I’ve covered a lot of ground in this essay. I began by presenting an energy-based framework with which to conceptualize human food systems that offers, as its benchmark, the need to adopt a food system with a positive energy balance. I presented data on the US food system, demonstrating that it is anything but energy-positive, and acknowledge that the only way we sustain it is by subsidizing it. We can’t afford to subsidize it forever, and if the flow of energy subsidies declines before we’re prepared to transition to energy-positive our food system will be compromised. I finally offer a range of questions to guide us in transitioning to an energy-positive food system.
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?
As we watch energy and food price volatility play out on the world stage, on the news, in the stock markets, on the shelves of our local supermarkets, it behooves us to ask some hard questions about the future of our food system. I’ve outlined several throughout this essay, some about agriculture, about our food processing strategies, our waste disposal processes, and our dietary habits. Although I focus on energy, it’s undeniably true that there’s more to food than just calories; I focus on energy because its assessment in the context of food systems is comparatively simple and it can serve as a unifying theme to drive our decision-making towards resilience. 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.
Although I ask many questions, I give few answers. This is deliberate. Food consumers – all of us – have played far too passive a role in the development of our food systems for far too long. Offering answers provides an excuse for people to remain passive, and I’m not convinced we can afford to do that anymore. 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 and Alison Nihart (University of Vermont), for offering valuable editorial and technical comments on this essay.
About the author
Eric Garza received his PhD from the University of Vermont in 2011. He consults in the energy, agriculture and food sectors and teaches courses in environmental pollution, energy systems and food systems at the University of Vermont. He manages the Path2Resilience.com website. For permission to reprint this essay, contact the author at [email protected].
 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).
 Hall et al. (1992) The distribution and abundance of organisms as a consequence of energy balances along multiple environmental gradients, Oikos 65: 377-390.
 For this graph I assume a deer consumes 24 ounces of acorns over a day, and that acorns contain 140 Calories per ounce for a total yield of 4,480 Calories. I assume the deer’s daily caloric requirement is 2,500 nutritional calories, of which 80 percent went towards basal metabolism and digestion and the other 20 percent went towards foraging.
 Mulder & Hagens (2008) Energy return on invested: towards a consistent framework, Ambio 37: 74-79.
 Lee & DeVore (1968) Man the Hunter, Sahlins (1972) Stone Age Economics.
 Canning et al. (2010) Energy Use in the U.S. Food System, report by USDA.
 Pimentel & Pimentel (2008) Food, Energy and Society.
 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.
 Hubbert (1949) Energy from fossil fuels, Science 109: 103-109.
 See the essay Energy, Economy and the Impending Rite of Passage.
 Wright (2004) A Brief History of Progress.
 Anderson (2006) Tending the Wild.
 Clark (2004) Benefits of re-integrating livestock and forages in crop production systems, Journal of Crop Improvement 12: 405-436.
 McDonough & Braungart (2002) Cradle to Cradle; Jenkins (2005) The Humanure Handbook.
 Weber et al. (2008) Food-miles and the relative climate impacts of food choices in the United States, Environmental Science & Technology 426: 3508-3513; energy costs of food transport are closely correlated with the greenhouse gas emissions tallied in this study.
 Katz (2003) Wild Fermentation, Katz (2012) The Art of Fermentation.
 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 Pimentel & Pimentel (2008) Food, Energy and Society.
 See Figure 4 in Mulder & Hagens (2008), cited above.
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