White Paper: Energy Use in Food
Jan 12, 2012 | Diet
This white paper was written for
GHSP Inc. to support the PBS series:
EARTH: THE OPERATORS' MANUAL
For an introduction to energy use in food, see our Overview & Tips
Of the many items we consume each day, food is one of the largest,at approximately 14 percent of annual U.S. energy consumption . This short paper describes the calculations behind the personalizedenergy-diet calculator prepared by WattzOn that helps usersunderstand the relative amounts of energy use to grow, process andtransport their food.
The goals of the energy-in-food calculator are:
· To provide information and create awareness about the role offood in our daily energy use.
· To provide suggestions as to how an interested consumer canreduce energy use by making alternate food choices.
· To provide information in a manner that engages consumers.
We have benefited from reviews of earlier drafts of this paper, and from user experience with our web tools during the summer andfall of 2011. This has shown us that food choices interact with ahost of other issues, including emotions about the nature of theU.S. food industry, carbon calculations and perceptions aboutpersonal diet and food choices. For example, Americans eat a lotof sugar, and some reviewers have reacted to energy-in-foodcalculations with judgments about this food choice.
Based on this early experience, we have focused the calculator andthis research note on the energy implications of food choices - asingle dimension of a multi-dimensional issue. There are manyelements of food and agriculture policy that affect climate change,diet and health, but these are beyond the scope of this work. Here,we maintain a narrow focus on personal energy use.
For most products and services, the item requiring the least amountof energy to make is also the item with the smallest greenhouse gas(GHG) emissions. This is not true for food. A diet heavy in beefwill have higher carbon content than a vegetarian diet, but theenergy required to make the two diets will not differ as much. Animportant source of carbon emissions in diet is animal-basedfoods. Animals themselves are producers of a significant amount ofemissions as they digest food. Food processing the livestock andpoultry does not require much more energy than processing in otherfood groups. So while eating less meat clearly reduces the CO2e(carbon dioxide equivalent) emissions, eating less meat does notstand out as a key action to reducing energy use.
THE WEB TOOL
At the WattzOn website, users can enter data about their diet toobtain estimates of energy use and CO2e emissions from the mix offoods. Users adjust their food choices via a slider, moving theicon right or left to increase or decrease the number of daily orweekly servings of the food group.
The food groups shown are: beef, pork, poultry, fish, dairy,grains, fruits and vegetables, and sweets. We provide the increaseddetail on animal-based protein sources, because the relative energyimpact versus CO2e impact varies sharply by protein source.
Users can enter data for a household or for an individual anddisplay in either mode, as well. The results are shown in terms ofBTUs (thermal unit) per household per year. The results can also bedisplayed in terms of pounds of CO2e.
The diet tool calculations are based on U.S. economy-wide dataon food consumption and food production. The basic concept is tomatch consumption and production by food type, thus obtaining thetotal energy used, to produce a total number of calories, which isthen divided to obtain the energy required to produce a singlecalorie of that food type. With user information, via the sliders,the annual energy use from diet choices can be estimated.
CALORIES AND SERVINGS
The USDA reports the average number of calories per capita perday by food type and the average number of servings per capita perday by food type. (The serving metric - cups, ounces, teaspoons- is also provided.) These data are reported each year, and tomatch the data on energy used in food production, calorie data from2002 is used. There has been a slight downward trend in the numberof calories and servings in recent years, but little year-to-yearvariation.
One of the important aspects of the USDA data is that it is "lossadjusted," meaning that food production and calories are net ofwaste. For example, if 150 calories of a food type are produced,but only 100 calories are available for use by the consumer due towaste, calculations that ignore waste will be significantly off. Food data net of waste is not always available and makes studiesdifficult to compare.
The Economic Research Service (ERS) of the USDA considers theseloss adjustments important, as the adjusted data more closelyreflect calories consumed and energy used. However, the ERS notesthat the adjustments are based on a few studies from the 1970s and1980s, and that the food supply chain has changed significantlysince then. Improved loss adjustments are an on-going projectat the USDA, and, meanwhile, a recent FAO study found that lossesin the North American food supply chain range from 6 percent ofproduct in milk to 45 percent or more in vegetables (FAO,2010).
In addition to food waste in the supply chain, there isconsiderable food waste at home. The FAO study found 25 percentfood waste in the home. Parfitt et al. (2010) cite the originalstudies used for these conclusions, which show in-home food wasteof 12-25 percent. For our calculations, we consider food caloriesavailable "at the front door". Wasted food still required energyto produce, and, thus, no explicit data adjustment is needed. There is, however, an opportunity to save energy by reducingin-home waste.
ENERGY AND EMISSIONS
Two key data sources are used that provide the energy consumedand the CO2e emitted in the production of food. The first is theEnvironmental Input-Output and Lifecycle Cost Analysis (EIO-LCA)database, developed and maintained by the Green Design Institute atCarnegie Mellon University (CMU), which tracks energy use and CO2eemissions by industry. The second is a recent study by theUSDA, Energy Use in the U.S. Food System. Both data sets are basedon the input-output tables of the U.S. economy, produced by theBureau of Economic Analysis (BEA).
Input-output tables provide a comprehensive view of the economy,tracking all inputs across all industries that are needed for theproduction of final goods. The BEA maintains a 480-sector table,the most detailed analysis of its type in the world. There are 28food sub-industries in the table. The latest BEA input-outputtable is based on 2002 data. The CMU and USDA studies are based onthe BEA work, and, thus, also present data from 2002.
The EIO-LCA model is the result of more than 15 years of researchat Carnegie Mellon University, and is a leading tool for lifecycleenvironmental impact analysis. Of particular importance forfood calculations is that the EIO-LCA model tracks energy use andCO2e emissions for the entire supply chain. For example, theestimates of the energy used to produce one pound of beef availableat a local grocery store will include, among other inputs, theenergy used to grow and transport the grain to feed the cattle, allenergy for packaging and processing, energy for the materials tobuild new processing plants in the meat industry, and energy totransport the refrigerated meat to the store. This list is notexhaustive, but merely illustrative of how the EIO-LCA model, basedon economy-wide input-output tables, captures the full lifecycleenergy use and CO2e emissions. As this is the standard breadth ofthe EIO-LCA model, the results are comparable for each foodinput.
A few data details and wrinkles: The EIO-LCA data report a singlesub-industry, "animal products," instead of its sub-groups of beef,pork and other meats. The USDA study provides this detail forenergy use. The USDA study overlaps with the EIO-LCA data on otherfood industries, and the overlapping data are much the same. TheCO2e data for the beef and pork are from another USDA study (USDA,2011d). The EIO-LCA energy and CO2e data are reported in terms ofdollars of industry output. Industry output per food sub-industryis from the U.S. Census for 2002.
MATCHING FOOD GROUPS TO FOOD INDUSTRIES
The USDA provides calories and servings data by food group, withdetail about items within a group. For example, under thevegetables group (48 calories per day, on average), data areavailable for the daily calories consumed for lettuce, tomatoes andmore.
A key piece of analysis in building the diet calculator is thematching of these food groups to food industries. This process isextremely important, as it ensures conformance between the datasets. In a few cases, a food item was moved from one food type toanother, for better conformance with food industry data. Forexample, ice cream is in the dairy food group for diets, but in thesweets food industry for these calculations. Using thesub-industry detail, it was moved to the dairy industry group tocreate a better match between food production and foodconsumption.
When constructing the diet calculator, we faced a tension betweenease-of-use and informative detail. As the food group detail wasadjusted to balance these factors, we also discovered that somesub-foods/sub-industries have less reliable results, due to smallconsumption or production. For example, the average American eats16 calories of fish per day, less than one serving. Given thisrelatively small amount, it is no surprise that the energy used toproduce a calorie is relatively high. And, as the 16 calories arethe total consumption from specific types of fish, each with aneven smaller number of calories, minute changes in the number ofcalories consumed by fish type will have a large effect on thecalculated energy use per calorie consumed. To avoid this problem,the food sub-industry groups are aggregated, when possible. Fishis treated as a separate source of protein, despite the potentialfor measurement errors, because of the strong consumer interest inthis food.
The final food groups in the calculator are:
· Fruits & Vegetables
Not shown in the list are "added fats and oils", which is 24percent of the calories consumed by the average American. This isa difficult food group to deal with, as most us would not knowwhere those nearly 600 calories go. To best capture the fullenergy profile of the food industry, while not confusing users, wedistributed the calories consumed from added fats and oils to otherfood groups by proportionately scaling up the number of servings,keeping the total calories consumed constant. Separately, energyused and CO2e emissions from added fats and oils were distributedto other food groups in the same manner.
In addition, 9 percent of the food industry's energy use is fromseasonings, sauces and miscellaneous items - again, a food groupthat is difficult to deal with. The calories, energy use and CO2ewere distributed to the other food and industry groups.
The adjustments for seasonings and fats preserve ease-of-use whilekeeping constant energy consumed, and CO2e emissions at theaggregate level. This is a reasonable approach, as the food items(sauces, seasonings and added fats) are consumed in conjunctionwith the other food groups.
Table 1 shows the results of these calculations. Descriptions oftypical serving sizes are from the Cleveland Clinic. Thecomposition of the average American diet is shown for 2,600 totalcalories per day. As mentioned earlier, these are calories beforeany food preparation waste in the home. Actual consumption will beless.
Note on Table 1 that the average American diet has a large numberof calories from grains and sweets, and few calories from fruitsand vegetables. As one shifts from the average American diet tohealthier alternatives, the caloric composition shiftssignificantly, as do energy use and CO2e emissions.
Table 1 shows relatively high BTU per calorie produced for fish,and also high CO2e emissions for this source of protein. Asmentioned earlier, this food group was broken out separatelybecause of consumer interest, but we do not have high confidence inthe data for fish.
Table 2 shows the same data in a different format, one thathighlights the relative energy intensity of various food groups. Because of concerns about the quality of the data for fish, thetable was prepared both with and without the fish food group. Theresults for CO2e are no doubt familiar to many readers. Beef isthe largest emissions producer, by far. In contrast, the column ofresults for energy use in food production shows much less variationacross food groups. In particular, beef is not an intense user ofenergy, but, in fact, is at or below average. This leads to aninteresting result: eat less beef to reduce emissions; eat lessfruits and vegetables to reduce energy use.
Table 2 highlights how examining food policy through a singleattribute - energy use or CO2e emissions - may miss other importantgoals, such as healthy eating. Food policy has multipleobjectives, and personal preference determines the balance point. Minimizing energy use might not be the most important goal for manypeople.
Table 3 below provides an overall perspective and presents resultsthat can be compared to those of other researchers. The tableshows the calories, energy use, and emissions associated with theaverage American diet. Note that the average American diet is aresearch product of the USDA, and is not likely to be the diet ofanyone you know. It is based on food production, adjusted forlosses. It is also adjusted for imports and exports. The USDA'saverage American diet is commonly used to show typical consumptionand its validity has been extensively researched.
Table 3 shows that consumption of proteins and grains are thelargest energy uses in our diet. (The sum of the protein rows, frombeef to fish, is 29 percent of daily BTUs on average.) Theconsumption of these food groups is also the largest emissions ofCO2e. Americans eat very few fruits and vegetables, only 12percent of calories, and increasing consumption of this food groupwill not save energy or carbon. Fresh vegetables, in particular,have a relatively high-energy intensity, due to the handling andrefrigeration of these perishable crops.
COMPARISONS TO OTHER WORK
The total CO2e emissions from the food calculations are linewith other carbon calculators, such as Jones and Kammen (2011), whoestimate from EIO-LCA data that food emissions are 7.7 CO2e metrictons per year. (Our estimate is 9.8 CO2e metric tons per year, withthe differences arising from the treatment of food away from home,miscellaneous food, the composition of the average diet, and soon.) Similarly, a data summary from the University of Michiganshows that the average American emits 8 metric tons of CO2e peryear from food choices. The same source also estimates that 48percent of emissions arise from beef and dairy consumption, and ourestimate is that 49 percent of emissions are from thesesources.
The energy results from the food calculations are line withEschel and Martin (2006) and the USDA, with about 15 percent oftotal energy use arising from food consumption for the averageconsumer.
It is important to note that congruence amongst estimates ofcarbon emissions and energy use for food is desirable, but may be alimited opportunity; results are highly dependent on methodology. Researchers have approached this complicated area quitedifferently. Here are some of the factors to consider whenevaluating studies, as often one is comparing "apples tooranges":
Defining the boundaries of the analysis. Forexample, the World Watch Institute includes many sources of landclearing in CO2e calculations. The CMU data uses older EPA data,and includes less of this item.
Inclusion of all food groups. For example,miscellaneous food, seasonings, and flavorings are nearly 9 percentof food industry energy, but are often omitted from food-emissionscalculators. Also, beverages are not included in diet or foodindustry data sources, though they consume energy and providecalories. For example, soft drinks and alcoholic drinks are anadditional 13 percent of energy use, above estimates from foodalone (based on EIO-LCA data).
Fuel conversions. The EIO-LCA uses a 31 percentfuel efficiency for electricity generated from coal plants. Otheranalyses do not distinguish between generation sources and keep allat 100 percent efficiency, and thus have much lower energy use andemissions.
Waste in the food supply chain. Some studiesaccount for this and some do not.
What is the objective function? For example,monoculture has bad effects that are not related to energy or CO2e.Additionally, there are fertilizer runoff problems. These areissues that change the relative value of food groups and aninformed consumer might want to consider them. Again, it is notclear that minimizing energy use is the single-decision criterionfor consumption or policy-making.
Our current diet. Many studies do not start withthe average American diet, and then vary food choices from thisreference point. For example, eating healthy per the Choose MyPlate diet recommended by the USDA will almost certainly reduceemissions - if less meat is eaten -- but, surprisingly, maysometimes increase energy use, depending on the specific fruits andvegetables and non-meat protein that replaces meat. The relativeimpact of diet choices must be measured against where we are, notwhere we wish we were.
The EIO-LCA data have been analyzed by others, and their researchsuggests additional recommendations. Weber and Mathews (2008)examine the transport component of energy use in the food system.They find that 83 percent of energy used comes from production, andthat only 4 percent of energy is used to transport food from theproducer to stores or restaurants. On average, food travels about1,000 miles during the production process, but the authors concludethat the average consumer can save more energy or emissions byshifting away from beef or poultry one day a week than by buyinglocal.
Typically, the food supply chain is assumed to end at the store orrestaurant. The consumer then drives to those locations to purchasefood. Weber and Mathews extend their analysis from simplytransportation in the food supply chain, to the miles driven topurchase food. They note that reducing annual driving by 1,000miles per year saves about the same amount of energy as does buyinglocal. Reducing driving by 1,100 miles per year saves the sameamount of energy as does shifting from animal to vegetable proteinsources one day a week. Of course, the specifics of any tradeoffwill depend on the particular vehicle and its mileage, but theauthors point out that it might be easier to make changes viadiet.
While the overall energy intensity of the U.S. economy has beendeclining, the food industry has been going in the oppositedirection. Energy use per capital has been raising energy use inthe food industry, largely from a shift to processed foods (USDA,2010). The change reflects the decline in cooking at home; energyuse from cooking, captured in utility bills, has dropped and energyuse in the food supply chain has increased. Total energy may nothave increased; energy consumption might just be a transfer fromone sector to another. It is difficult to draw the conclusion of"buy fewer packaged foods and cook more at home to saveenergy."
Finally, although the data are not recent or as complete as onewould like, it does appear that there is considerable opportunityto reduce energy and emissions in food consumption by wastingless. The FAO study and the USDA estimates suggest considerablewaste in the food supply chain, but importantly for thesecalculations, there is also considerable waste in the home. Arecent report by the USDA suggests that consumers waste asignificant of calories purchased, with the exact amount varying byfood group (USDA, 2011c). So, reducing wasted food at home canmake a significant savings in energy and emissions.
SUGGESTIONS FOR SAVING ENERGY OR REDUCINGEMISSIONS
· Eat less. One-third of adults are obese in theUnited States, consuming more calories than needed. Eating is avery emotional issue, and we doubt that adults will eat less tosave energy, but the math of food intake is clear.
· Buy less and waste less. Estimates are that12-25 percent of food purchased is wasted in the home. More carefulfood purchasing can be a large source of energy savings.
· Eat fewer grain products. More than 35 percentof the energy in the average American diet comes from the grainsfood group. Further, many grain products have added fats and oils,and/or added sugar, which are another 20 percent of energy in thediet. In sum, 55 percent of energy and 60 percent of calories arefrom grains, sugars, and fats. Because of its large share of thecurrent American diet, this can be a place to reduce.
In addition, analyses by others using the same data suggestthat:
· Buying local has only a small impact on energy and emissions,because most food energy is from production, nottransportation.
· Driving to the store to purchase food uses more energy per yearthan does transporting food to the store.
· There are large waste losses in the food supply chain, andreduction of this waste throughout the industry can lower theenergy content of food significantly.
· Energy use in the food industry has risen as Americans cook less.We continue to shift our purchases to prepared foods. An example iswashed and bagged lettuce.
BEA (2011), Benchmark Input-Output Tables for 2002. www.bea.gov/industry/io_benchmark.htm.
Eschel and Martin (2006), "Diet, Energy and Global Warming,"Earth Interactions, 2006, http://pge.uchicago.edu/workshop/documents/martin1.pdf.
FAO (2010), Global Food Losses and Food Waste, downloaded from:www.fao.org/fileadmin/user_upload/ags/publications/GFL_web.pdf.
Hendrickson et al. (2006), "Environmental Life Cycle Assessmentof Goods and Services, An Input-Output Approach". Resources forthe Future, 262 pages.
Jones and Kammen (2011), "Quantifying Carbon Footprint ReductionOpportunities for U.S. Households and Communities,"Environmental Science & Technology, downloaded from:http://pubs.acs.org/doi/abs/10.1021/es102221h.
Parfitt et al. (2010), "Food Waste within Food Supply Chains:Quantification and Potential for Change to 2050," PhilosophicalTransactions of the Royal Society, B, downloaded from:http://rstb.royalsocietypublishing.org/content/365/1554/3065.abstract
Weber and Mathews (2008), "Food-Miles and Relative Impact ofFood Choices in the U.S.," Environmental Science andTechnology. Downloaded from: psufoodscience.typepad.com/psu_food_science/files/es702969f.pdf.
USDA (2010), "Energy Use in the U.S. Food System," EconomicResearch Service, downloaded from: www.ers.usda.gov/Publications/err94/err94.pdf.
USDA (2011a). See "Average Daily per Capita Calories from theU.S. Food Availability, Adjusted for Spoilage and Other Waste,"www.ers.usda.gov/data/foodconsumption/spreadsheets/foodloss/Calories.xls.
USDA (2011b), "Loss-Adjusted Availability, by Servings."www.ers.usda.gov/Data/FoodConsumption/FoodGuideSpreadsheets.htm#servings.
USDA (2011c), "Consumer-Level Food Loss Estimates and Their Usein the ERS Loss-Adjusted Food Availability Data," Economic ResearchService, downloaded from: www.ers.usda.gov/Publications/TB1927/.
USDA (2011d), "U.S. Agriculture and Forestry Greenhouse GasInventory: 1990-2008; Chapter 2: Livestock and Grazed LandEmissions"; www.usda.gov/oce/climate_change/AFGG_Inventory/2_LivestockandGrazing.pdf.
World Watch Institute (2011), Livestock and Climate Change;
 14 percent (USDA, 2010)
 For consumer interest, other metrics may be displayed on theweb tool, but as each can be translated into units of energy orCO2e, the discussion here will focus only on these two.
 See USDA (2011a) and (2011b).
 This discussion is available at www.ers.usda.gov/data/foodconsumption/FoodGuideDoc.htm.
 The EIO-LCA model is available in an interactive form fromCarnegie Mellon University, at www.eiolca.net/cgi-bin/dft/use.pl. The producer priceversion of the model was used. Data on the energy use and CO2eemissions by food sub-industry were obtained, per $100 million ineconomic activity. The total 2002 economic activity by foodsub-industry was obtained from the EIO-LCA model documentation,www.eiolca.net/docs/full-document-2002-042310.pdf.Energy use was then normalized to millions of BTUs per capita,using 2002 population estimates of 287.8 million residents (U.S.Census, http://www.census.gov/popest/data/historical/2000s/vintage_2002/index.html).
 The data are available at eiolca.net, USDA (2010) and BEA(2011), respectively.
 For an introduction to the model, see www.eiolca.net.
. The industry sales data was downloaded from: http://factfinder.census.gov/servlet/IBQTable?_bm=y&-geo_id=&-ds_name=EC0231I1&-_lang=en.
 There is a large literature on the two methods used by theUSDA to determine what Americans eat (a food consumption survey andthe production data used in this work), and much discussion abouttheir strengths and weaknesses. Our intent here is to simplypresent an easy-to-understand reference point.
 Center for Sustainable Systems, University of Michigan.2010. "Carbon Footprints Factsheet". Pub. No. CSS09-05.
 Center for Disease Control, 2010 data: www.cdc.gov/obesity/data/trends.html.