Rethinking sustainable eating: vegetarian diets reduce greenhouse gas emissions

A paper has just been published in The American Journal of Clinical Nutrition that strikes a chord close to my heart.  Researchers have combed the literature studying the relationship between diet and greenhouse gas emissions, and have determined that vegetarian diets reduce emissions and are much more sustainable compared to meat-based ones.  There has been much discussion about this already among environmentalists indicating that, if most of the world ate a largely vegetarian diet, greenhouse gas emissions would decrease due to the lessened methane emissions from cow flatulence (yes, it’s true!) and the reduced dependence on fossil fuels used to transport meat.  This seems to be the first study to synthesize the various findings out there and present a cohesive picture.

Being a vegetarian, these findings resonate with how I see the world, but I think it’s important to emphasize that the study finds that just lessening meat consumption, not ridding of it entirely, can significantly decrease emissions.  I’ve never wanted to proselytize my way of life, mainly because I don’t think it works, and I think just aiming to reduce meat consumption is a much more tenable goal for most of the population.  So with that in mind, let’s get into the details…

Figure courtesy of

Figure courtesy of

Have you ever considered whether you eat a sustainable diet?  I have often considered whether I live a sustainable lifestyle – limiting car use, walking when I can, buying local, etc. – but a sustainable diet actually encompasses a quite detailed set of requirements.  According to this article, a sustainable diet has been defined as ‘ protective and respectful of biodiversity and ecosystems, culturally acceptable, accessible, economically fair and affordable; nutritionally adequate, safe and healthy; while optimizing natural and human resources’ – can you say your diet meets all those standards?  I just finished eating a box of donuts, so I know I have work to to do.  But I think it’s an important concept to keep in mind as we move toward a more climate and impact-conscious society.  Seems like a good goal to work towards.

This paper in particular focused on the environmental element of sustainability – namely, the efficiency of energy use and environmental protection related to vegetarian- versus meat-based diets.  Efficiency is the amount of energy used to gain some amount of energy in food, and environmental protection quantifies the amount of damage (or lack thereof) to the environment as a result of acquiring either veggies or meat.  This could be global warming, forest destruction, reduced biodiversity, etc. caused by the veggie-growing or meat-producing industries.

Figure courtesy of [1]

Figure courtesy of [1]

Pictures usually make a point much better than words, and this graph really hits home the main point of the article regarding efficiency.  The graphics represent all the various methods of gathering food, from basic agriculture and hunting/gathering on the left to mainstream, megafarm cow- and chicken-raising on the right.  The y-axis gives a ratio of energy in divided by energy out.  Therefore, anything above one is technically unsustainable because you’re getting less energy in food than what you put in with labor, chemicals, solar energy, etc.!   Notice that most of our modern methods of animal raising are far above one.   Free range beef and low-intensity eggs, favorites of the modern organic and local movement, are just below one, which is promising, but nothing compares to the original hunting/gathering and agriculture of old.  This is a profound graph to me – so much said with such simple data.  Modern society has become worse, in a sense, at getting food energy out of input energy.  So much for the benefits of technology, it seems.

Figure courtesy of

Figure courtesy of

How can this be?  The original methods of food production relied mainly on solar energy to grow crops – the input energy was the sun and the human labor of a farmer or two.  Not much energy required, one farmer working a field of a variety crops, and plenty of food on the table at the end of the day (maybe a bit too idyllic, but that’s the general idea).  Now, after discovery of fossil fuels, we input a great amount of energy in terms of chemicals, irrigation systems, etc. to produce huge quantities of one type of food per farm, the so-called monoculture.  Data from the article, originally reported by  the Center for Sustainable Systems, indicates that 40% of the energy input to modern farms is used for chemical fertilizers and pesticides.  The majority of the other 60% goes to transport, storing, and serving.  Only 20% goes to on-farm production!  In addition, most of this additional energy relies on fossil fuels, a finite energy source, making modern industrial food production unsustainable.

So what do we do about it?  The answer this paper provides is to focus on vegetables.   As they describe, we lose energy every time we move up the trophic chain to more complex types of food (animals being higher up than vegetables).  So we feed grains to cows, so we can later eat the cows, but if we just ate the grains, we would be nourished and use up less energy.  That’s the gist.   Here’s what the paper found in a nutshell regarding the ratio of mass input to mass output of food for various types of meat:

Figure courtesy of [1]

Figure courtesy of [1]

We need 13 kg of grain to get just one kg of beef to eat, and the fossil fuel to protein energy ratio is even worse (right column).  This table alone sums up the environmental argument for the vegetarian diet (along with the graph above).  These data do also indicate that eating chicken or turkeys will be a much more sustainable option.   Much of this energy loss comes from the fact that, according to the article, producing animal protein requires 6-17 times greater land use than for other, soy-based proteins.

Figure courtesy of [1]

Figure courtesy of [1]

But we still need our protein, right?  The authors have an answer there, as well.  This plot above graphs all protein sources as a function of amount of protein in the food source (x-axis), and the efficiency with which is was produced (y-axis).  All the meat-based proteins definitely do well in protein content, as they are far to the right along the x-axis, but very poor in efficiency, as we discussed, being low on the y-axis.  On the other hand, soy-based proteins, peas,oats, and others do as well as a protein source per kg and are much more efficiently produce (upper right).

So there are options out there!  Try making a black bean burger!  It definitely does require an adventure in cooking and getting used to new tastes, flavors, textures, etc., though.  And I would imagine that is the main obstacle preventing most people from transitioning to vegetarian diets.  We all want to protect the environment, but at what cost?  Eating is a comfort, a social pastime, a stress reliever, and meats have probably become comfort foods of a sort.  We can throw all this data at people, but it is the emotional ties to food that keep us strapped to our habits.  This makes me think I should start posting good vegetarian recipes on this site…

Figure courtesy of [1]

Figure courtesy of [1]

I’ll leave you with one last bit of evidence for why moving towards the vegetarian spectrum of eating is a service to your planet.  Here, the authors have calculated the CO2 emissions per capita in the UK based on average, vegetarian, and vegan diets.  The main takeaway is that vegetarian and vegan diets reduce greenhouse gas emissions by over 20%.

So for those looking for a noble pursuit, becoming vegetarian truly does assist with this global goal of limiting greenhouse gases.  It is a way as an individual to use his or her daily lifestyle to contribute to this global cause.  Even reducing meat intake by having a ‘vegetarian night’ or two will help in the long run.  It is this way of thinking that best combats those who think a dietary revolution is unrealistic.  Everything appears unrealistic when we are far from the reality of it, but small steps slowly take us closer, until we forgotten from where we’ve  started and we believe the new normal is how it’s always been.



Sabate, J., & Soret, S. (2014). Sustainability of plant-based diets: back to the future American Journal of Clinical Nutrition, 100 (Supplement_1), 476-482 DOI: 10.3945/ajcn.113.071522

This entry was posted in Article Reviews, Climate Change, Energy, Energy and Society. Bookmark the permalink.

6 Responses to Rethinking sustainable eating: vegetarian diets reduce greenhouse gas emissions

  1. julien says:

    What’s on the x-axis on the second picture you show? Protein content ? Energy content ? Time?

    • jptrinastic says:

      Thanks for reading! The article doesn’t have the x-axis labeled, but you can take it to be time. Initial agircultural methods and basic hunting/gathering are shown on the left, and more industrialized methods are introduced as we move right. I agree, not the most clear!

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