Quantifying The Small Body Problem: A Meta-Analysis Of Animal Product Reduction Interventions
Background
The farmed animal protection movement deploys diverse strategies, including interventions designed to encourage individuals to reduce, or entirely eliminate, their consumption of animal products. As animal advocates and organizations launch and refine these campaigns, it becomes crucial to strategize around unintended consequences.
Substitution of one animal product for another can be an undesirable outcome for animal product reduction interventions, and poses a particular problem when a smaller-bodied animal product is substituted in place of a larger one. When people reduce their consumption of large-bodied animal products (e.g., pork, beef) but compensate by consuming more small-bodied animal products (e.g., chicken, fish) rather than plant based substitutes, animal suffering is heavily compounded. How so? This substitution impacts many more animal lives, given the number of individual animals needed to fill the same demand. For example, nearly 200 chickens are required to produce the same amount of meat gained from slaughtering a single cow. This phenomenon is known in the farmed animal advocacy space as “the small body problem” and has even received attention in popular media.
Concerningly, two of the most prevalent appeals used to get people to reduce their animal product consumption — environmental appeals and health appeals — focus heavily on reducing red meat consumption and may explicitly favor the uptake of other animal products, such as fish or chicken. In light of the small body problem, this presents a major animal welfare concern. However, it remains unclear how prevalent the issue of substitution is and how concerned animal advocates ought to be about it when implementing reduction/elimination interventions. If meat reduction efforts risk unintentionally pushing people toward more small-bodied animal consumption, and thus costing more animal lives, animal advocates must be mindful of (1) the factors that lead to small-body substitution and (2) the best practices for guiding consumers toward plant proteins instead.
To address current ambiguity regarding the small body problem, Faunalytics and Bryant Research conducted a meta-analysis to evaluate evidence of a substitution effect in interventions designed to reduce or eliminate animal products from participant diets. That is, we investigated whether consumption of specific animal products ever increases in response to an intervention, even if overall animal product consumption decreases. Although we looked for evidence of increases across all edible animal products (EAPs), we were most interested in small-bodied animal products (e.g., fish and chicken). We also used the available evidence to analyze the intervention characteristics that were associated with substitution effects, allowing us to provide recommendations to advocates.
Key Findings
- More research is vital. The meta-analyses undertaken in this report had statistical limitations, as there simply were not enough studies at our disposal to run the most robust and informative tests. Moreover, the studies currently at hand are highly variable, making it difficult to draw strong conclusions. We highly encourage advocates to conduct more studies on possible substitution effects that can be incorporated into meta-analyses such as the ones we report here.
- Overall, we found no evidence of the small-body substitution problem in response to animal product reduction interventions. On the whole, people do not appear to increase their consumption of small-bodied animals (e.g., chickens, fishes) when exposed to animal product reduction interventions. However, this comes with the caveat that studies were highly variable, meaning that some interventions did actually result in greater small-bodied animal consumption, even when the overall result — with all studies considered — was null.
- Overall, people did not decrease their consumption of animal products (neither large- nor small-bodied) when exposed to animal product reduction interventions. This may be alarming to advocates, as it implies that current advocacy strategies are ineffective. However, this is slightly reductive. Findings indicate that positive and negative results across the studies are canceling one another out, producing an overall null result. With this in mind, specific intervention types that do show success should be prioritized (see the fourth Key Finding). Moreover, new, innovative approaches ought to be considered.
- Despite no overall effect, some individual interventions did result in reduced animal product consumption. Choice architecture in particular was associated with reduced consumption of small-bodied animals. We recommend advocates incorporate choice architecture into their efforts whenever possible to maximize impact.
Recommendations
When carrying out interventions that aim to reduce and/or eliminate the consumption or purchase of animal products, we make the following recommendations.
For Advocates
- When possible, implement choice architecture. Choice architecture strategies (e.g., menu alterations that elevate plant-based options, pairwise displays of meat alternatives at supermarkets, etc.) were associated with a significant reduction of small-bodied animal product consumption/purchase. While evidence is currently limited, we consider choice architecture a safe bet for advocates wishing to avoid triggering the small body problem. Existing evidence suggests that choice architecture steers clear of the small body problem while also moving the needle in a favorable direction, nudging people to lessen their consumption of small-bodied animals. Resources for further reading:
For Researchers
- Replicate past work. Currently, we do not have enough studies to contribute to a deeply informative meta-analysis. We are attempting to converge studies that use entirely different mediums and appeals, that are implemented over entirely different timeframes, and that measure entirely different outcome variables. This diversity at first appears to be a benefit, allowing us to distill findings across the full spectrum of reduction/elimination interventions — from leaflets to university courses to eco-labels on cafeteria offerings. However, in doing so, we limit our ability to adequately distinguish between interventions. Splitting up the data to only compare like with like does not solve the problem either. For example, if we opted to only look at “health appeal” interventions, we would be left with a mere six interventions to analyze. Or if we wished to investigate interventions whose medium is a university class session, module, or course, we would only have three interventions at our disposal.
For a robust meta-analysis that is able to capture both the forest and the trees, more studies are needed — and not just more studies, but more studies that resemble one another. To assess whether eco-labels on food products trigger an uptick in chicken or fish consumption (i.e., small body replacement), we simply need more eco-label studies. To assess whether health is an effective appeal — which does not backfire by increasing small-bodied animal consumption — we need more studies using a health appeal. So on and so forth. In essence, we need more replication studies, studies at least similar enough in concept and execution that we are comparing Honeycrisp and Golden Delicious rather than apples and oranges. For more on this, please see our Conclusions. - Make use of this report’s accompanying resources. This recommendation is two-fold. First, we highly encourage researchers to use our open-sourced data to expand investigations into the small body problem. Researchers can download our datasets, include additional studies as they are published, and use our R script to run analyses. As the number of relevant studies grows, robust and nuanced analyses of the small body problem become possible. The investigations within this report are merely the first foray.
We believe our data complements existing meat reduction intervention databases (e.g., these by Rethink Priorities and LIME), as ours specifies granular details per study, including but not limited to the body size/species of the animal products consumed. However, we would like to note that LIME’s features in particular are still expanding. LIME currently allows users to conduct their own meta-analyses directly in the platform, based on various outcome and intervention characteristics that can be toggled on and off. All types of meat are currently aggregated, meaning that, at the time of writing, this tool cannot be used to investigate the small body problem. However, this tool is still in beta, with new features being actively added. We highly encourage researchers to explore the site.
Second, we encourage researchers to use our materials in other contexts, wherever they find relevant. Our datasets offer detailed information across a litany of studies, from quantitative data points (e.g., means and sample sizes) to qualitative characteristics (e.g., each intervention’s medium, timeframe, and appeal). This collated information can be used outside of the small body problem context, and we hope advocates will take full advantage.
Applying These Findings
We understand that reports like this have a lot of information to consider and that acting on research can be challenging. Faunalytics is happy to offer pro bono support to advocates and nonprofit organizations who would like guidance applying these findings to their own work. Please visit our virtual Office Hours or contact us for support.
For an in-depth, accessible overview of this study’s findings in video format, be sure to check out the webinar below.
Behind The Project
Research Team
The project’s lead author was Elise Hankins (Bryant Research). Dr. Allison Troy (Faunalytics) provided primary review and oversight of the work, with Dr. Andie Thompkins (Faunalytics) offering additional support. Dr. Jo Anderson (Faunalytics) provided concept development and theoretical direction.
Acknowledgements
We would like to thank the authors of numerous studies who provided access to their unpublished data and materials, allowing us to include results previously unseen by the public. We would also like to thank Constanza Arévalo for her work on earlier iterations of this project, and Rethink Priorities for their feedback on this study. We are sincerely grateful to the EA Funds’ Animal Welfare Fund for their support of this project.
Research Terminology
At Faunalytics, we strive to make research accessible to everyone. We avoid jargon and technical terminology as much as possible in our reports. If you do encounter an unfamiliar term or phrase, check out the Faunalytics Glossary for user-friendly definitions and examples.
Research Ethics Statement
As with all of Faunalytics’ original research, this study was conducted according to the standards outlined in our Research Ethics and Data Handling Policy.
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Citations:
Hankins, E., Thompkins, A., & Troy, A. (2025). Quantifying The Small Body Problem: A Meta-Analysis Of Animal Product Reduction Interventions. https://faunalytics.org/quantifying-the-small-body-problem/

