A Review of Environmental Life Cycle Assessments of Diets: Plant-Based Solutions Are Truly Sustainable, even in the Form of Fast Foods

Round 1

Reviewer 1 Report

29-Jun-2021

Reviewer(s)' Comments to Author:

These are specific comments that have to be addressed:

 

Manuscript Sustainability -1289853 with title " A Review of Environmental Life Cycle Assessments of Diets: Are plant-based solutions truly sustainable, even in the form of fast foods? " provides an interesting research to develop Environmental Life Cycle Assessments of the three main diet types, omnivore, vegetarian, and vegan, and then assesses the environmental impacts of adding two commercial brands of plant-based burgers to vegetarian and vegan diets.

 

I have the following comments:

ABSTRACT

Please clarify the purpose of the research.

Please revise your methods.

 

RESULTS and DISCUSSION:

There are too many Flow chart. Perhaps consider linking them or showing them more clearly or showing them in Appendix. 

 

CONCLUSION

Please write conclusion more clearly. Revise your findings and originality of the research and should provide a clear scientific justification for the research. The most important findings (results) should be more emphasized. 

Author Response

We thank the reviewer very much for these constructive and extremely helpful comments. 

Response to Reviewer 1 Comments:

Point 1: ABSTRACT: Please clarify the purpose of the research.

Response 1:

We have revised the abstract to state clearly the objective of this paper. See lines 7-9 of the revised manuscript.

 

Point 2: ABSTRACT: Please revise your methods.

Response 2:

We have added a method section, which includes the material formerly presented as supporting information. The new section follows the MDPI guidelines and provides the information to check the PRISMA criteria. The new methods section is in lines 72-126 of the revised manuscript.

 

Point 3: RESULTS and DISCUSSION: There are too many Flow chart. Perhaps consider linking them or showing them more clearly or showing them in Appendix. 

Response 3:

The paper presents three flow charts, one for a beef patty and two for each of the plant-based alternatives considered. We explored options for merging them but we could not found a solution that would allow us to communicate the information included in the analysis.

 

Point 4: CONCLUSION

Please write conclusion more clearly. Revise your findings and originality of the research and should provide a clear scientific justification for the research. The most important findings (results) should be more emphasized

Response 4:

We have modified the beginning of the conclusions section to emphasize the findings of the paper. See lines 681-683 in the revised manuscript.

Reviewer 2 Report

Please see attached file.

Comments for author File: Comments.pdf

Author Response

We thank the reviewer very much for these constructive and extremely helpful comments. 

Response to Reviewer 2 Comments:

This study uses existing literature to assess environmental life cycle analysis of three different diets, two plant-based, and an omnivorous diet. They conclude that industrial processing of plant-based meat alternatives has lower environmental footprints relative to a regular, 80/20 burger. The issues examined are timely and relevant, and I enjoyed reading the article. Below are comments the authors would hopefully find helpful.

Response:

Thanks so much for all of your comments. They were constructive and extremely helpful. We have tried our best to follow your suggestions and think the paper has significantly improved as a result.

 

Main Points

Point 1: In the introduction, include a sentence that explains why it is less efficient to feed grains to livestock than humans. How is efficiency being measured? (Re: lines 37 to 39, page 1).

Response 1:

We have included a sentence that explains that feeding grains to livestock is less efficient than feeding them to humans because only 4-20% grains protein becomes edible animal protein. (See lines 47-48 in the revised manuscript).

 

Point 2: Beneath Table 1, you explain the asterisk to be the estimated impact of vegetarian and vegan diets reported by the two literature reviews….. What are the two literature reviews?

Response 2:

We have added a sentence to the asterisk in the caption to clarify that the two reviews are those from Hallstrom et al., 2015 and Alexandriwicz et al., 2016.

 

Point 3: In relation to the above, what does the double asterisk mean (See Peters et al. 2016)?

Response 3:

We have modified Table 1’s caption with a note for the double asterisk: ** It studied two reference diets based on actual consumption and eight modeled “healthy diets”.

 

Point 4: I am struggling to see the relevance in the discussion of the Fair comparison section, 2.1. Is it to suggest that you used protein and caloric content as standards in your work? It doesn’t look like it.. 

Response 4:

We have modified the structure of sections 2 and 3. In the revised manuscript, section 2 now describes the review protocol and comparability of results of the reviewed papers (Lines 73-126), while section 3 and 4 present all the findings (lines 127-558). We have significantly shortened the text of what previously was section 2.1 in the original manuscript and have included it as part of the methods, where its relevance becomes clear.

Also, we have deleted the confusing statements about protein content and have clarified that all the modeled diets have comparable caloric content and nutritional values (see lines 104-126 in the revised manuscript).

 

Point 5: Under sub-section 2.2, is there a standard baseline for omnivorous diets (eg, 2000kcal/person/day)? From your explanation though, it appears different studies used different standards, and if that is the case, how did you compute relative changes across different studies? A discussion of that in the text would be helpful.

Response 5:

10 of the 15 studies had a baseline of 2000kcal/person/day, another four studies had higher baselines for caloric intake, and one did not use caloric intake as a functional unit. Nevertheless, within each study, the different diet types were assessed using the same functional unit. This allowed calculating, for each study, percentage reductions from vegetarian and vegan diets relative to omnivorous diets. We have clarified this in the methods section, in lines 104-117 of the revised manuscript.

 

Point 6: Is representing footprints with different colors the norm in the literature? If not, limit this to the descriptions for the graphs and use only what they represent in the text. For example, blue water use represented vegetarian diets at one point, and at other times represents the volume of surface and groundwater used to produce a crop. The lack of consistency can be confusing.

Response 6:

We agree that choosing blue and green to represent vegetarian and vegan diets in the figures causes confusion because of the early references to the classifications of water use into blue and green. To avoid confusion, we have edited Figure 1, changing the colors to represent the impact reductions from vegetarian and vegan to purple, and orange. See revised manuscript, line 220.

 

Point 7: The “Collective Results” on page 13 is perhaps the most salient insofar as your study goals are concerned. As such, it would be important to expand and discuss this better, well before the discussion on “Findings” for Beyond and Impossible burgers.

Response 7:

We have expanded the section of Collective results discussing the impacts reductions as a percentage of the beef’s impact estimate and presenting conservative estimates of impact reductions. Our discussion now makes a stronger case of how the introduction of vegan and vegetarian burgers cannot reduce the environmental benefits of these diets. To aid the discussion we have expanded Table 3 presenting two e ranges of impacts reductions, one relative to the best estimate of beef impacts and the other a conservative estimate of reductions, using the lower bound of beef’s impacts estimates. See revised manuscript, lines 510-535. In addition to this, we have added a subsection with a discussion on the environmental benefits of partial replacement of beef in an omnivorous diet, with plan-based burgers (lines 536-558). To aid readers’ comprehension of these impact reductions, we have presented them in the context of more relatable quantities such us, GHG emissions by cars, area deforested, or per-capita water consumption.

 

Point 8: Measured on a functional unit bases, plant-based diets/meat options are unambiguously better for the environment. However, this overlooks the role of an expanding plant-based industry increasing cases of deforestation and habitat destruction. While this doesn’t take away from the merits of your work, it should at least be discussed.

Response 8:

We have added a few sentences on soybean production, deforestation, and soy-based foods. We focus on soybean because according to Sabine Henders et al. 2015 (Environ. Res. Lett. 10 125012) four commodities (beef, soybeans, palm oil, and wood products) account for 40% of deforestation in seven countries with high deforestation rates (Argentina, Bolivia, Brazil, Paraguay, Indonesia, Malaysia, and Papua New Guinea). See lines 568-576 in the revised manuscript.

 

 

Minor Points

Point 9: Page 2 line 63: the searching protocol that led, not lead.

Response 9:

Thanks so much for pointing to this typo. Because we have included a new method section and rephrased the text describing the searching protocol, we are no longer using the word “led”.

 

Point 10: In sub-section 2.1, please define FU (line 96) before you start to use it

Response 10:

Thanks so much for pointing to this. We have defined FU (Functional Unit) the first time this term is mentioned in the paper. See line 119 in the revised manuscript.

 

Point 11:  What decisions informed summarizing 15 research studies, or was it arbitrary?

Response 11:

Section 2 in the revised manuscript now describes the search protocol that led to the 15 research studies reviewed and the objective of this review. See lines 79-90.

 

Point 12: In Table 1, what does “Review” mean for Hallstrom et al’s. (2015) study?

Response 12:

We have replaced the word review, in Table 1, with the sentence “Review of 14 journal articles with 49 diet scenarios”. For consistency, we have also replaced the description of the other review paper, Aleksandrowicz et al. “Review of 63 studies with 210 diet scenarios”. See Table 1 at line 133.

 

Point 13: Page 4 lines 108 to 110. Please rewrite the sentence: It helps to ensure that if diet A……. same sentence: …. Lower environmental impacts THAN diet B, not “that.” The whole sentence needs a rewrite though. 2

Response 13:

We have re-written this sentence in lines 119-122 of the revised manuscript.

 

Point 14: In sub-section 2.2, be explicit in the text that “blue water use” represents a vegetarian diet, and a vegan diet for “green water use.”

Response 14:

We have clarified that we are not making a distinction between blue and green water use, and we have also changed the colors in Figure 1 to avoid confusion. Lines 257-260 in the revised manuscript read “Studies typically measure blue and green water consumption as water use and consider grey water in a separate category, such as pollution or eutrophication potential. For the studies discussed in this review, green and blue water consumption are considered collectively as a metric of total water consumption.”

 

Point 15: Under Water Use, change the font of the first two words to conform with the rest.

Response 15:

We have changed the font size of the first two words to make consistent with the rest. See line 253 in the revised manuscript.

 

Point 16: On page 6 line 179, I believe you mean “Grey,” not Gray

Response 16:

We have replaced “gray” for “grey”. See line 254 in revised manuscript.

 

Point 17: In Figure 2, please consider using more distinct colors to separate legumes from eggs

Response 17:

We have changed the color of eggs to white and the pale pink of legumes to a darker pink. We also changed the color of fruits to yellow and the color of meat to brown to avoid confusion with other shades of green. See line 320.

 

Point 18: Page 8 and line 282 should be “These ingredients” or “The ingredients.”

Response 18:

We have added an apostrophe to clarify that we are referring to the list (of ingredients) so the correct pronoun is “this”. See line 359 in revised manuscript

 

Point 19: In Figure 3, please use more distinguishing colors for blue versus green.

Response 19:

We have edited Figure 3, replacing the blue and green for the more distinguishing colors of purple and pink. For consistency, this change has also been applied to Figure 4 and Figure 5.

 

Point 20: It would be informative to explain what aquatic eutrophication is.

Response 20:

We have added an explanation on line 648-649 of the revised manuscript “….that contribute to eutrophication, which alters the composition and diversity of aquatic plants and disrupts the ecosystem and food web, …”.

 

Point 21: Page 13 line 435: Edit sentence – This paper compared the …. Or This paper review

compared ……

Response 21:

We have edited the sentence so it now says “This paper compared ..”. See line 562 in the revised manuscript.

 

Point 22: Be consistent with your in-text references. Some have the published years, other do not. Others have the years in parenthesis, but not all. See for example pages 3 and 4

Response 22:

We have added the published years to all the in-text references.

 

Reviewer 3 Report

While this article offers interesting results, some revisions are required:

- the first paragraph in the introduction needs to be further explained and justified, and also these two statements: “low meat, vegetarian (no meat), and vegan (no meat, eggs, or dairy) diets have significant environmental benefits in comparison to prevailing dietary trends in wealthy countries” and “new plant-based burgers may be the solution to this conundrum if two conditions are met: a) meat eaters can accept them as a perfect substitute, and b) they indeed are more sustainable”.

- the authors should better articulate the identification of the research gap.

- since the authors claim that they present a paper which is based on a review of published studies, they should add an independent section to explain the method used. A proper method section would include the supporting information (it should be moved from the annex to the text) with an expansion and justification of its rationale. The authors should follow the publishing standards and guidelines of MDPI which reveal that PRISMA covers systematic reviews and meta-analyses.

- the authors should revise the structure and flow between sections and sub sections 2 and 3, and describe the structure of the paper in the introduction.

Author Response

We thank the reviewer very much for these constructive and extremely helpful comments. 

Response to Reviewer 3 Comments:

While this article offers interesting results, some revisions are required:

Response:

We thank the reviewer very much for these constructive and extremely helpful comments.

 

Point 1: the first paragraph in the introduction needs to be further explained and justified, and also these two statements: “low meat, vegetarian (no meat), and vegan (no meat, eggs, or dairy) diets have significant environmental benefits in comparison to prevailing dietary trends in wealthy countries” and “new plant-based burgers may be the solution to this conundrum if two conditions are met: a) meat eaters can accept them as a perfect substitute, and b) they indeed are more sustainable”.

Response 1:

We have clarified the first sentence by replacing “prevailing dietary trends” with “more carnivorous dietary trends”. See line 43 in revised manuscript.

We have also clarified the second sentence by replacing “meat eaters can accept them as a perfect substitute” with “consumers can accept them as a meat substitute”.

 

Point 2: the authors should better articulate the identification of the research gap.

Response 2:

We have modified the last paragraph of the introduction to clarify the intention of this review. The new paragraph reads: “This paper investigates the second condition, asking whether less-healthy plant-based diets, those that abstain entirely from animal products but include high shares of industrially processed meat-substitutes, have the lowest environmental footprint. How are the environmental impacts of a vegan diet affected, in terms of land use, water use and green-house emissions, when highly processed plant-based meat substitutes are included? This paper reviews published LCA studies to shed light on this question and summarize the consensus on the sustainability of vegetarian and vegan diets.” See lines 62-70. We have also modified the abstract. See lines 7-9 of the revised manuscript.

 

Point 3: since the authors claim that they present a paper which is based on a review of published studies, they should add an independent section to explain the method used. A proper method section would include the supporting information (it should be moved from the annex to the text) with an expansion and justification of its rationale. The authors should follow the publishing standards and guidelines of MDPI which reveal that PRISMA covers systematic reviews and meta-analyses.

Response 3:

We have added a method section, which includes the material formerly presented as supporting information. The new section follows the MDPI guidelines and provides the information to check the PRISMA criteria. The new methods section is in lines 73-126 of the revised manuscript.

 

Point 4: the authors should revise the structure and flow between sections and sub sections 2 and 3, and describe the structure of the paper in the introduction.

Response 4:

We have added a description of the structure of the paper (lines 70-72) and have modified the structure of sections 2 and 3. In the revised manuscript, section 2 now describes the review protocol and comparability of results of the reviewed papers (Lines 72-126) while sections 3 and 4 present all the findings (lines 127-559)

Round 2

Reviewer 2 Report

The authors have responded to all substantive comments in this round of review and I do not have further comments.

Author Response

We thank the reviewer very much for all the valuable comments submitted during the first review. We are glad we have addressed those comments to satisfaction.

Reviewer 3 Report

While the authors have revised some of the previous recommendations, some revisions would improve the paper:

- the statements added at the end of the abstract should be removed. The implications and conclusion of the research should be explained.

- in the method, please summarize how you followed the PRISMA protocol in a graphic format and justify the different steps (for example, the use of databases) with previous research.

- the authors should revise some section titles because section 4, 4.3 and 5.1 are all titled as the findings.

Author Response

Please see attached file.

Author Response File: Author Response.pdf