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Meat vs Veg: An Energy Perspective

What ought we eat? This is among the preeminent questions of our time, one asked by policy wonks, diet gurus and, of course, consumers. People imbue a wide array of values into their dietary choices, including impacts on their health, cost and environmental impacts, among others. The question of what to eat generates a particularly generous array of fireworks when it pits plant eaters – vegans and vegetarians – against consumers of animal flesh.

I’ve spent time as both a vegan and vegetarian, adopting both practices due to ethical concerns regarding how meat is raised in the United States. As I’ve learned about the array of management practices available to animal farmers I’ve opened to eating animal-derived foods again, and have also taken up hunting. Beyond this, I do life cycle energy audits within the agricultural sector as part of my profession, and I’ve accumulated enough data to see a fascinating story emerge regarding one particular impact of food production: its energy intensity. In this essay I’ll present data on the energy intensity of animal- and plant-derived foods and hopefully contribute to a constructive dialog about what we ought to eat and how we ought to be producing it.

Before there’s data though, there needs to be a framework for presenting and understanding it. I’ve adopted the return on investment framework, comparing the energy inputs used by a food production enterprise, measured in calories, to the calorie value of foods produced.1 These two pieces – energy inputs and food energy output – can be combined into a tidy ratio that acknowledges the fundamental truth that modern industrial agriculture turns industrial energy sources that we can’t eat into food energy that we can, while also offering a sense of the efficiency of this conversion process. When the ratio is presented as inputs divided by outputs, a number larger than one indicates a system that’s input-intensive, so the smaller the input/output ratio the better.

Data from the United States Department of Agriculture affords an opportunity to look at the energy intensity, using the above input/output framework, of several classes of foods produced in the US.2 The ‘production’ phase of these foods includes agriculture, animal husbandry and, for wild-caught fish, harvest. Processing includes butchering animals, washing and packaging crops, or other more involved processing techniques. Distribution includes transportation as well as wholesale and retail sales. While these categories make up a substantive part of the energy invested in food production, they don’t represent the totality of it. Energy used by restaurants and caterers, within households to store and prepare food, and by water treatment facilities and waste disposal sites, among other categories, are not included, guaranteeing that the numbers presented are underestimates.

The energy intensity, measured as industrial calorie inputs per food calorie output, for several classes of food in the United States.

The energy intensity, measured as industrial calorie inputs per food calorie output, for several classes of food in the United States.

The energy inputs associated with animal-derived products are high. This fact shouldn’t surprise anyone; the production of these foods – even seafood – is an industrialized process from start to finish, requiring large pieces of machinery, sophisticated processing facilities, industrially-produced feed, and refrigerated transportation. All of these elements require huge investments of energy, either directly as fuel to power them or indirectly in their manufacture and maintenance. The energy intensity of fruit and vegetables in the US might surprise some, but it shouldn’t. Modern fruit and vegetable farming systems are highly industrialized, relying on vast monocultures that require fertilizers and pesticides that are energetically costly to produce and apply as well as tillage practices that require heavy machinery and plenty of fuel. While grain is less energy intensive than other foods, it is relatively devoid of easily absorbed nutrients due to the presence of plant secondary compounds that bind minerals and as commonly consumed provide little more than empty calories. At the national level, there appears to be little meaningful difference between the energy intensity of animal-derived foods compared to fruits and vegetables, and some animal foods such as eggs and dairy products are actually less energy intensive.

Most food activists I meet are disillusioned with the large-scale food production operations represented by the above data, and are more interested in supporting smaller farms and the shorter supply chains they use to deliver their products to local and regional markets. I’ve done life cycle energy audits of several small farms in the northeastern US, and the data tells an interesting story. These audits count both direct energy use, including electricity, diesel and other fuels used on the farm, and indirect energy, including fuels used to manufacture machinery, building materials and other farm inputs. By looking at both direct and indirect energy I’m able to paint a fairly complete picture of energy use within farming enterprises, although the audits leave out some processing segments as well as higher stages of local food supply chains. In the graphics that follow, fuel refers to the direct and indirect energy associated with fuels like diesel, gasoline and electricity, among others, while the numbers associated with vehicles, machinery, buildings and inputs are estimates of indirect, or ‘embodied’, energy. Labor includes both the calories burned by workers on the farm as well as the energy used to transport them to and from work.

Industrial energy inputs per calorie of food produced for two small vegetable farms.
Industrial energy inputs per calorie of food produced for two small vegetable farms.

The graphic at right shows the energy intensity of two certified organic vegetable farms, one that operates as a CSA and a second that markets its produce through farmers’ markets and wholesale. The non-CSA farm grew 55,000 pounds of vegetables during the year of my audit, or about 8.5 million calories of food. Most of the energy use on this farm is embodied energy in the soil amendments, particularly compost, needed to maintain soil fertility in the face of heavy tillage. Fuel use is divided between on-farm use to power machinery and off-farm use for deliveries and transport to farmers’ markets. The CSA produced 236,000 pounds of produce, equating to just over 42 million calories. The largest share of energy use on this farm is fuel, some of which powers farm machinery while much of the rest heats greenhouses used to extend the short growing season. Part of the reason fuel use is small for this farm is because customers must drive to the farm to pick up their CSA shares, effectively shifting the fuel use associated with deliveries onto customers. The embodied energy of soil amendments is smaller, because fewer are used per calorie of produced food.

These two operations show how radically different two operations that yield similar types of food products can be in terms of their energy intensity. On-farm management practices can make huge differences in the energy intensity of an operation, as can decisions on how to distribute products. I don’t assume that these farms necessarily represent both ends of the efficiency spectrum; I suspect I’ll come across plenty of fruit and vegetable farms that are more energy intensive than either of these over the course of my career, and perhaps some that are more efficient. The challenge of vegetable and fruit operations is that the foods produced are not particularly calorie dense, so shipping adds disproportionately higher energy costs compared to foods, such as animal products, that carry more calories per gram.

Industrial energy inputs per calorie of food produced for two pastured meat operations.
Industrial energy inputs per calorie of food produced for two pastured meat operations.

And speaking of animal products, let’s look at a couple meat operations. The graphic at left shows energy consumption for two pasture-based operations. The lamb farm produced just under 13,000 pounds, or 14 million calories, of marketed meat. The largest share of this farm’s energy use is the diesel used to move trailers of sheep from one tract of pasture to another, as the farmers can’t afford a single large piece of land and must spread their pastures across several parcels that are geographically separate. The rest of the liquid fuel transports sheep to the slaughterhouse, picks the cut and packaged meat up and finally delivers it to customers. The embodied energy of grain fed to the sheep as a dietary supplement makes up about half of the farm input category, while the remainder is attributable to soil amendments. The other farm produced just over 16,000 pounds of meat, mostly pork but also a smaller amount of beef, totaling just over 11 million calories. Liquid fuels like gasoline and diesel comprise most of the fuel use, and the proprietors of this farm must also drive animals among geographically separate parcels to maintain their grazing plan and drive them to a distant slaughterhouse. The huge energy demand associated with farm inputs is made up primarily of the embodied energy in grain purchased to feed pigs; while ‘pasture raised’, pigs raised on a commercial scale generally get a minority of their food from the pasture and receive most of their nutrition from grain-based feed.

As with the vegetable operations, these meat farms don’t necessarily represent best and worst practices; I’m sure I’ll encounter operations that are better and worse than either of these. One challenge that hinders meat operations is the need to transport animals to slaughter and packing facilities instead of processing them on-farm as is legally done by fruit and vegetable growers. State and federal regulations require off-farm slaughter in specialized facilities for most meat destined for resale, and this institutionalized inefficiency is thankfully being reconsidered in some areas, with exemptions for certain types or scales of livestock producers emerging that allow for transport energy savings while ensuring that animals are slaughtered humanely and butchered in a sanitary manner. If these exemptions become more widespread, livestock operations would certainly see substantial gains relative to vegetable and fruit farms in terms of energy efficiency.

Industrial energy inputs per calorie of food produced for a small diversified farm.
Industrial energy inputs per calorie of food produced for a small diversified farm.

Finally, the graphic at right shows the energy use profile of a diversified farm that sold 30,000 pounds of bread, 40,000 pounds of vegetables and 21,000 pounds of pasture-raised beef, pork and milk. This equates to roughly 67 million calories of food. The largest share of the farm’s energy use comes in the form of farm inputs, mainly the manufactured bags used to package bread. Soil amendments are also important, while purchased grain, hay and bedding materials make up a lesser share. Electricity is the most important fuel used on this farm, while diesel and gasoline are important for shipping animals to slaughter and making deliveries, although much of the farm’s food is sold through an on-site farm shop. This diversified farm is less energy intensive than any of the other farms I’ve featured, and this isn’t an accident. The ability to integrate animal and vegetable operations into a cohesive whole adds a layer of ecological efficiency to the operation that more specialized farms can’t touch. My observation that small, diversified farms seem to be an increasingly popular pursuit among small farmers is telling, and comforting.

Modern food systems turn industrial fuels into food. As I pointed out in my essay on the energy basis of food security, high and volatile energy prices inspire many to wonder how much longer we can afford to depend on this industrial model, and perhaps a time is coming when economic forces will favor a different model. While I’d never claim that energy input/output figures should singularly drive food system design considerations, the preeminence of energy throughput to industrial society suggests to me that energy efficiency should certainly be an important factor.

Vegetables and fruit are obviously a necessary component of a healthy human diet, contributing calories as well as a wide array of plant secondary compounds with nutritional and medicinal benefits. Animal foods also contribute by offering complete protein and necessary fatty acids, at least when pasture raised in a way that affords animals access to a diverse, plant-based diet. As the debate continues on the role that animal-derived foods can and should play in our food system, I hope that the data I’ve presented here injects clarity into discussions that focus on the energy efficiency of these two classes of foods. Vegetables and fruits are not inherently less energy intensive, and pastured meats are not necessarily more so. I look forwards to gathering additional data on this subject, and making it available to aid others in developing management practices that yield resilient and profitable agricultural systems.

Notes

  1. A calorie (lowercase ‘c’) is a thermal unit used in many contexts, while a Calorie (uppercase ‘C’) is 1,000 calories and is often called a nutritional calorie or kilocalorie. I use the word ‘calorie’ to mean a nutritional calorie, or a kilocalorie, because it’s what most people are accustomed to.
  2. US food system energy use data are from the USDA’s report Energy Use in the US Food System (Canning et al, 2010) and from the USDA’s Economic Research Service. Estimates of food availability corrected for waste and spoilage are called ‘loss-adjusted’ by the USDA, and are used as a proxy for food that’s eaten by a person.

Photo credit: Wikipedia

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