Impact of Diets on the Environment

[Dean Pomerleau]

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 [1] 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 [1]:

 

 

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 [2] (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

 

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[1] 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

 

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[2] 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.

[Sthira]

This is very disappointing. For much of my life I've been a vegan and vegetarian for environmental and ethical reasons. So wow. This isn't so great to hear.

[Dean Pomerleau]

I hear you Sthira.

 

Note: this study does not claim to suggest that it is impossible to eat an environmentally-friendly & healthy vegan/vegetarian diet, but that one has to choose one's foods wisely, and focus on getting the bulk of one's calories from categories like legumes, nuts/oils, whole grains, and soy products, which have the lowest environmental impact.

 

Unfortunately, at least some of us (including me) focus on eating a lot of fruits and vegetables for health reasons, which are not so great for the environment from the perspective of water and energy usage.

 

--Dean

[LizC]

Surely eating so much LESS has got to count for something, right?

[Dean Pomerleau]

Liz,

 

Surely eating so much LESS has got to count for something, right?

 

The main results of the study actually took into account a shift to eating fewer calories - about 200 calories fewer calories on average relative to what people consume today (est. ~2400kcal/day). But it was still an average of ~2200 per day, which is likely higher than most CR practitioners eat - or at least assimilate... The shift to the healthier recommended foods (more fruit, vegetables, dairy and seafood) swamped the effects of eating 200 fewer calories per day, so that the environmental impact of eating fewer, but better calories was greater than the estimated baseline diet. 

 

--Dean

[Sthira]

I guess y'all've seen this story copied by Al?

 

http://www.cbc.ca/news/technology/headlines-suggesting-vegetarian-diets-are-environmentally-unsound-are-misleading-author-1.3375218

 

Headlines suggesting vegetarian diets are environmentally unsound are misleading: author

Not all vegetables are created equal, says co-author of attention-grabbing study

 

By Khalil Akhtar, CBC News Posted: Dec 21, 2015 10:31 PM ET Last Updated: Dec 22, 2015 3:12 PM ET

 

A newly-published study says some vegetables can have a large environmental impact. But the study's co-author notes not all vegetables are created equal.

 

A newly-published study says some vegetables can have a large environmental impact. But the study's co-author notes not all vegetables are created equal. (CBC)

 

It's a message that's been repeated by animal rights groups like PETA, environmental organizations like the David Suzuki Foundation, and even the United Nations — the most environmentally-friendly diet choice you can make is eating less meat, if not an entirely vegetarian diet.

 

Which is why a newly-published study raised a lot of eyebrows, and generated headlines proclaiming that vegetarian diets might actually be harmful to the environment.

 

As it turns out, though, those headlines weren't quite capturing the real story.

 

The common argument has been that diets lower in meat can reduce greenhouse gas emissions and, if enough of us do it, we could put a dent in the meat industry and reduce climate change.

 

CBC Radio's the Current recently hosted a panel that made that argument.

 

Water-guzzling beef

 

"Meat is having a really major impact on our environment," according to panelist Laura Wellesley. She's the co-author of a report from the British think-tank Chatham House, called Changing Climate, Changing Diets: Pathways to Lower Meat Consumption.

 

'Simple rules like "go vegetarian and you'll reduce your footprint" can certainly be true, but are not always true.'- Paul Fischbeck, study co-author

 

"A large share of the emissions — about two-thirds of the emissions — come from the livestock themselves, so their digestive processes and also their manure," she told the Current.

 

"And around a further sixth comes from the production of crops for animal feed. And of course, you have carbon dioxide emissions as well from the transportation of animal products, heating and cooling of buildings, use of machinery, etcetera."

 

Beef, she said, is particularly notorious for being environmentally unfriendly. According to a report from the London-based Institution of Mechanical Engineers, it takes more than 15,000 litres of water to produce a kilogram of beef, thanks in part to the water-heavy alfalfa and forage used to raise cows.

 

Lettuce vs. bacon

 

Hence the surprise when Carnegie Mellon University researchers published a study with a seemingly contrarian conclusion.

 

The university even put out a news release with an attention-grabbing headline that said "Eating Lettuce Is More Than Three Times Worse in Greenhouse Gas Emissions Than Eating Bacon."

 

Lettuce 'happens to have a relatively large impact on the environment,' says Carnegie Mellon University's Paul Fischbeck. (Getty Images)

 

Paul Fischbeck is a professor of engineering and public policy at Carnegie Mellon, and was one of the study's authors. And he says the headline is accurate — but not the entire story.

 

"Lettuce is a relatively fragile vegetable. It requires lots of water to grow," he said.

 

"It's not very dense. And so you get a truckload of lettuce, it doesn't weigh very much, but you still have to drive that truck. It has to get to the market relatively quickly, it has to get home, there's a lot of food loss along the way. And so if you look at the farm-to-fork analysis, lettuce happens to have a relatively large impact on the environment."

 

Not all vegetables created equal

 

But that's not the only point that Fischbeck and his co-authors make in their study, which points out that not all vegetables are created equal.

 

Fischbeck said he doesn't doubt that beans, nuts, and seeds are highly efficient and sustainable foods. But lettuce, for example, is not — nor are water-rich foods like eggplant, cucumber, and celery.

 

To explain, Fischbeck's study compares calories. If you were to replace, say, 100 calories of bacon — about two pieces — with 100 calories of cucumber, you'd need to eat more than six cups of the vegetable to get the same number of calories as you would through the bacon.

 

processed meat

 

A slice of bacon provides about 50 calories. You'd need to eat more than three cups of sliced cucumbers for the same calorie intake. (Jennifer Quesnel/CBC)

 

That's why on paper, replacing bacon calorie-for-calorie with vegetables like lettuce or cucumbers would be highly inefficient — simply because it would lead to the production and shipping of massive volumes of produce.

 

"Simple rules like 'go vegetarian and you'll reduce your footprint' can certainly be true, but are not always true," Fischbeck said.

 

"Is it better to have a simple message that may in fact be less accurate, or to have a more nuanced message that is in fact more accurate? This is a classic problem when it comes to communication of information to the public."

 

And on the subject of nuance, Fischbeck says the news coverage of his study didn't have a lot. Some of the headlines on stories about the research might have lead to the belief that a bacon-rich diet could save the planet.

 

It won't, so don't try, according to Fischbeck, who says such headlines make for grabby journalism, but bad communication.

 

 

Environment Systems and Decisions pp 1-12 First online: 24 November 2015

Michelle S. Tom1, Paul S. Fischbeck, Chris T. Hendrickson

Energy use, blue water footprint, and greenhouse gas emissions for current food consumption patterns and dietary recommendations in the US

http://link.springer.com.sci-hub.io/article/10.1007/s10669-015-9577-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.

[Michael R]

The headline isn't justified, as already pointed out: they just compared Standard American Diet to reducing Calorie intake within SAD, switching over to a diet consistent with the Guidelines, or switching to a diet consistent with the Guidelines and reducing Calories. None of this has anything to do with going vegetarian: the headlines come from the fact that the Guidelines do suggest eating less meat, selectively, than SAD, and more vegetables (which, for what I have to assume is a quirk of etymological association, people wrongly specifically associate with vegetarianism, as when a vegetarian tries to make things easy for an omnivorous host by just filling up on side dishes, instead of bringing a pack of tofu burgers to throw alongside the beef ones on the barbie).

 

To make a true comparison of the environmental impacts of omnivorous vs. vegetarian diets, you have to do the latter kind of switching: not an apples-to-apples basis, but a steak-to-tofu basis, exchanging meat products for vegetal products that serve teh same functions in the diet.

 

That said, as the authors of this study do point out in the article and some of the press pieces, it really will matter which animal and vegetal sources you pick to make the switch: there's a very surprising difference in, eg. lettuce vs. spinach (see this infographic from the Wasington Post). Advocates of vegetarianism often make the reverse error of these press pieces, and pretend that vegetarian and meat-based diets are effectively all unprocessed, and directly compare meat with either grains or soybeans, and ignore not only vegetables but the processed meat substitutes that are a likely real-world substitute for meat rather than soybeans and rice.

 

I haven't seen a study that doees this in detail. WaPo mentions "six other studies, all cited by the federal committee providing expert advice to Dietary Guidelines for Americans, indicated that diets including less meat are better for the environment. To take but one example, Cornell University researchers reported in the American Journal of Clinical Nutrition in 2003 [this is clearly (1) below] that “meat-based food system requires more energy, land, and water resources than the lactoovovegetarian diet.” But (1) is exactly the kind of unsustainable "eat more of the side dishes" approach I mocked above:  "In the lactoovovegetarian diet, the meat and fish calories were replaced by proportionately increasing most other foods consumed in Table 1 in the vegetarian diet except sugar and sweeteners, fats, and vegetable oils."

 

A much better study is (2), focusing on diets using specific single-item switching of animal products to vegan equivalents ("cheese varieties made from cow milk and directly from lupine [sic: they mean lupins!] ... fish protein and vegetable protein ... and processed protein food based on soybeans and meat protein"). It finds:

 

a variety of environmental impacts associated with primary production and processing are a factor 4.4-> 100 to the disadvantage of meat. The comparison of cheese varieties gives differences in specific environmental impacts ranging between a factor 5 and 21. And energy use for fish protein may be up to a factor 14 more than for protein of vegetable origin. Assessment suggests that on average the complete life cycle environmental impact of nonvegetarian meals may be roughly a factor 1.5-2 higher than the effect of vegetarian meals in which meat has been replaced by vegetable protein. Although on average vegetarian diets may well have an environmental advantage, exceptions may also occur. Long-distance air transport, deep-freezing, and some horticultural practices may lead to environmental burdens for vegetarian foods exceeding those for locally produced organic meat.

 

And, again, see the WaPo infographic above.

 

References

1: Pimentel D, Pimentel M. Sustainability of meat-based and plant-based diets and the environment. Am J Clin Nutr. 2003 Sep;78(3 Suppl):660S-663S. Review. PubMed PMID: 12936963.

 

2. Reijnders L, Soret S. Quantification of the environmental impact of different dietary protein choices. Am J Clin Nutr. 2003 Sep;78(3 Suppl):664S-668S. Review. PubMed PMID: 12936964.

 

[Dean Pomerleau]

Thanks Michael!

 

I agree with your (and others') assessment that the headlines (e.g. 'lettuce is worse than bacon for the environment') aren't a fair or complete depiction of what this study found. Nonetheless it was surprising as you suggest how much worse some foods (vegetarian or otherwise) were for the environment than others.

 

That is a great table from the Washington Post article you pointed to. Since you didn't include it as a graphic in your post (presumably since it was in html format and not directly displayable), I've taking the liberty of creating a screen capture of it, since I think its interesting enough that people will want to see it despite perhaps being too lazy to click on it  .

 

As you can see from the chart below, lots of animal products do badly, but so do a lot of fruits and vegetables popular with CR folks. Its nice to see that nuts and sweet potatoes are near the bottom (best). Its strange they didn't analyse more legumes, although the two they did analyse, lima beans and peanuts (yes, peanuts aren't nuts, they're legumes), are near the bottom of the list (i.e. best) suggesting that other legumes are probably also pretty good for the environment relative to other foods. Grain products appear to be the very best my this metric.

 

--Dean

 

[AlPater]

The Impacts of Dietary Change on Greenhouse Gas Emissions, Land Use, Water Use, and Health: A Systematic Review.
Aleksandrowicz L, Green R, Joy EJ, Smith P, Haines A.
PLoS One. 2016 Nov 3;11(11):e0165797. doi: 10.1371/journal.pone.0165797.
PMID: 27812156
Free Article
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0165797
Abstract
Food production is a major driver of greenhouse gas (GHG) emissions, water and land use, and dietary risk factors are contributors to non-communicable diseases. Shifts in dietary patterns can therefore potentially provide benefits for both the environment and health. However, there is uncertainty about the magnitude of these impacts, and the dietary changes necessary to achieve them. We systematically review the evidence on changes in GHG emissions, land use, and water use, from shifting current dietary intakes to environmentally sustainable dietary patterns. We find 14 common sustainable dietary patterns across reviewed studies, with reductions as high as 70-80% of GHG emissions and land use, and 50% of water use (with medians of about 20-30% for these indicators across all studies) possible by adopting sustainable dietary patterns. Reductions in environmental footprints were generally proportional to the magnitude of animal-based food restriction. Dietary shifts also yielded modest benefits in all-cause mortality risk. Our review reveals that environmental and health benefits are possible by shifting current Western diets to a variety of more sustainable dietary patterns.

>>>>>>>>>
"Although the water use scenarios had smaller sample sizes, they showed somewhat similar trends across sustainable diet types, with vegetarian diets having the largest benefit (median -37%), though with the notable exception of the single vegan scenario showing an increase in water use (+107%) (Figs 2–4)."

[Thomas G]

I wonder if this is the kind of study that can make the numbers look very different depending on how you slice them. They are looking at environmental impact on a per calorie basis, but if you sliced the data on a per nutrient basis I bet meat would look like it has much worse environmental impact. Eating 2000 calories of lettuce has more environmental impact than 2000 calories of pork, but is that really all that surprising? If you heap up 2000 calories of pork next to 2000 calories of lettuce, the shear volume of lettuce would be huge in comparison.

 

What if you fed someone as much pork as they wanted until they said they felt satiated and then compared the environmental impact to the amount of lettuce someone eats until they fell satiated? Just in terms of the environment, would it be better to "fill up" on pork or on lettuce?