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There has been a lot of popular press coverage with headlines like Why It's Bad To Go Vegan: Lettuce Three Times Worse Than Bacon In Creating Greenhouse Emissions focusing on a new study  from researchers at my alma mater (Carnegie Mellon University), investigating the environmental impact of different foods and diets. Their results, if true (and after reading the full text, they seems pretty rigorous and convincing), are surprising and somewhat troubling, particularly for smug vegans (like me ) and others who consume a healthy diet low in meats, but high in fruits, vegetables, seafood and some dairy. From the CMU press release that accompanies the paper: [E]ating the recommended “healthier” foods — a mix of fruits, vegetables, dairy and seafood — increased the environmental impact in all three categories: Energy use went up by 38 percent, water use by 10 percent and GHG )greenhouse gas) emissions by 6 percent. "Eating lettuce is over three times worse in greenhouse gas emissions than eating bacon," said Paul Fischbeck, [CMU] professor of social and decisions sciences and engineering and public policy. "Lots of common vegetables require more resources per calorie than you would think. Eggplant, celery and cucumbers look particularly bad when compared to pork or chicken." “What is good for us health-wise isn’t always what’s best for the environment." Here is the most interesting and important graph from the full text of : It shows the energy use, "blue water" footprint (surface and groundwater required to produce the food) and greenhouse gas emissions for various food categories when compared on a per calorie basis. One thing that is strange it that the authors didn't break out legumes as a category, which I think would come out looking good. While meats and seafood were worst for greenhouse gas emissions, fruits in particular, along with vegetables and seafood require the highest amount of energy to produce and transport per calorie. While other studies have also found that meat production is a large contributor to greenhouse gas emissions, they've generally also found that the water footprint of meats was high as well, contra to what this current study found. And meats are worse for water usage than some categories of vegetarian foods, like grains fats/oils and sugar. But it would appear the combination of higher energy density in meats, coupled with the fact that farm animals are typically fed low-impact foods (like grains) in a highly optimized factory farm setting, couple to make their water footprint relatively modest, especially compared with fruits, which require a lot of water to produce and provide relatively few calories. The same analysis seems to be true for energy usage - i.e. high for fruits and vegetables because of low calorie density, and high energy cost for production and transportation. Here is the popular press discussion of the study titled A Study Did NOT Actually Find That Vegetarianism Hurts The Planet that I found most insightful and balanced by a reporter who actually interviewed the researchers. [T]he researchers behind this new study say that’s a total mischaracterization of what they found [referring to the idea that meat eating good, vegetarianism bad] . Rather, in terms of environmental impact, it turns out that not all foods in a particular food group are created equal, Michelle Tom and Paul Fischbeck of Carnegie Mellon University told The Huffington Post. “You can’t lump all vegetables together and say they’re good,” Fischbeck said. “You can’t lump all meat together and say it’s bad.” But sadly, what I think it is reasonably safe to conclude from this study is that a diet that is healthiest for people, and that many of us CR practitioners eat (i.e. heavy in all kinds of fruits and vegetables, with some nuts, seeds, whole grains, legumes, perhaps with modest amounts of seafood and dairy, but little meat), isn't necessarily the healthiest diet for the planet. Even more sadly, the foods groups that have the lowest impact on the environment are added sugars, grains and refined oils - foods that many of us try hard to avoid. Perhaps we can atone for our environmental sins by growing some of our own fruits/vegetables, and by composting, that latter of which this new study  (accompanying press release) in the journal Compost Science & Utilization (who knew...) found to be quite beneficial for reducing greenhouse gas emissions when compared to throwing food scraps in the trash, which produces a lot more methane when the scraps decay in a landfill. --Dean ---------  Environment Systems and Decisions pp 1-12 First online: 24 November 2015 Energy use, blue water footprint, and greenhouse gas emissions for current food consumption patterns and dietary recommendations in the US Michelle S. Tom , Paul S. Fischbeck, Chris T. Hendrickson Full text via sci-hub.io: http://link.springer.com.sci-hub.io/article/10.1007%2Fs10669-015-9577-y Abstract This article measures the changes in energy use, blue water footprint, and greenhouse gas (GHG) emissions associated with shifting from current US food consumption patterns to three dietary scenarios, which are based, in part, on the 2010 USDA Dietary Guidelines (US Department of Agriculture and US Department of Health and Human Services in Dietary Guidelines for Americans, 2010, 7th edn, US Government Printing Office, Washington, 2010). Amidst the current overweight and obesity epidemic in the USA, the Dietary Guidelines provide food and beverage recommendations that are intended to help individuals achieve and maintain healthy weight. The three dietary scenarios we examine include (1) reducing Caloric intake levels to achieve “normal” weight without shifting food mix, (2) switching current food mix to USDA recommended food patterns, without reducing Caloric intake, and (3) reducing Caloric intake levels and shifting current food mix to USDA recommended food patterns, which support healthy weight. This study finds that shifting from the current US diet to dietary Scenario 1 decreases energy use, blue water footprint, and GHG emissions by around 9 %, while shifting to dietary Scenario 2 increases energy use by 43 %, blue water footprint by 16 %, and GHG emissions by 11 %. Shifting to dietary Scenario 3, which accounts for both reduced Caloric intake and a shift to the USDA recommended food mix, increases energy use by 38 %, blue water footprint by 10 %, and GHG emissions by 6 %. These perhaps counterintuitive results are primarily due to USDA recommendations for greater Caloric intake of fruits, vegetables, dairy, and fish/seafood, which have relatively high resource use and emissions per Calorie. Keywords Energy use Blue water footprint GHG emissions Food consumption Diet ----------  Compost Science & Utilization Volume 24, Issue 1, 2016 DOI:10.1080/1065657X.2015.1026005 pages 11-19 Greenhouse gas accounting for landfill diversion of food scraps and yard waste Sally Brown ABSTRACT Diverting organics from landfills to compost piles is generally recognized as a means to reduce greenhouse gas emissions. This article provides a detailed review of the Climate Action Reserve (CAR) and the U.S. EPA Waste Reduction Model (WARM) protocols on landfill diversion and composting for food scraps and yard waste. The primary benefits associated with diversion are methane avoidance. The equations used to quantify methane avoidance include first-order decay rate constants for different feedstocks to predict how quickly organics will decay. The total methane generation potential of the different feedstocks is also included. The equations include estimates of gas collection efficiencies in landfills. The decay rate constants have been determined from laboratory incubations and may not be representative of decomposition within a landfill. Estimates of gas capture efficiency have been improved and more closely reflect actual landfill conditions. Gas capture efficiency will vary based on landfill cover material, portion of the landfill where measurements take place, and whether the gas collection system is operational. Emissions during composting are included in these calculations. Only the WARM model includes a consideration of benefits for compost use. Nevertheless, significant benefits are recognized for landfill diversion of food scraps. The WARM model suggests that landfilling yard waste is superior to composting.