Animal Charity Evaluators’ Better for Animals: Evidence-Based Insights for Effective Animal Advocacy resource is an ongoing project in which we distill key research on different animal advocacy interventions to help us evaluate their impact in different contexts. We have made this research publicly available to support informed decision making about how to help the most animals. You may read more about the methodology in our recent announcement.
This is a living document and we want to make it as helpful, accessible, and up-to-date as possible, so please feel free to reach out with feedback! To keep up to date with ACE’s research and the work of the amazing organizations that we support, be sure to sign up for our mailing list.
To help make this information more accessible to a wide range of audiences, we are spotlighting one intervention each month through a series of social media and blog posts. This month—for the second edition—we are focusing on the evidence around veg*n pledges.
Intervention Spotlight #1: Veg*n Pledges
What is this intervention?
This category refers to running vegan or vegetarian (veg*n) pledges to promote individual dietary change. Veg*n pledges are commitments from individuals to eliminate or reduce their animal product consumption for a specific period of time. Organizations typically campaign to achieve signups to their pledge program, and then keep in touch with participants over the course of their commitment, with varying levels of support and information provided. A prominent example is Veganuary. Veg*n pledges likely have other outcomes too, such as increased public awareness of veg*nism and promoting plant-based foods through corporate partnerships.
Summary: What is our overall assessment of this intervention? How confident are we in this assessment?
Even though Veganuary follow-up surveys report very high success rates, there are several findings that make us uncertain about the effectiveness of veg*n pledges:
Studies that randomly assign participants to pledge conditions are rare, and those that exist generally find that pledges are effective mostly in the short term (i.e., for the duration of the pledge). However, there are considerable uncertainties when generalizing these experimental findings to real-world campaigns.
Veganuary’s own conclusions rely on retrospective self-reports of Veganuary participants who responded to the follow-up survey, which may skew toward the most engaged among the overall pool of participants.1 Measuring dietary choices through self report is also often unreliable due to factors such as memory recall errors and social desirability bias, where individuals consciously or unconsciously misreport their animal product consumption, especially when primed to consider the ethical consequences of their food choices.2
It seems likely that many people who self select into participating in veg*n pledges already reduce their meat consumption or intend to do so. Therefore, it is possible that they would have further reduced their consumption anyway, without the intervention. However, it is also possible that pledges kickstart or otherwise facilitate this process.
Well-known challenges such as Veganuary can leverage their popularity to build corporate partnerships and encourage retailers to increase their plant-based options. This can lead to increased plant-based sales driven by changes to the food environment (e.g., prominent product placement) and active promotion of plant-based options (e.g., through price reductions), but has not been robustly shown to decrease animal product sales.
Based on the available evidence, we tentatively think that veg*n pledges appear to be a less promising intervention among those we assessed, at least for creating new, sustained diet change in the general population. This is a broad, preliminary assessment and we expect the effectiveness of any intervention to vary significantly depending on the context and the approach taken:
We believe this intervention is likely stronger when:
The ask is stricter: Two studies suggest vegetarian or vegan pledges outperform flexitarian or reduction pledges.
Participants have higher starting motivation and are already reducing animal products before the pledge.
There is social support during the pledge, e.g., encouraging participants to involve friends and family.
The participants have access to readily available veg*n alternatives and ongoing support throughout the pledge period.
Conversely, the intervention is likely weaker when:
The ask is looser (for example, a generic reduction or flexitarian pledge).
Participants have low initial motivation, limited access to acceptable alternatives, or receive little support during the pledge.
Participants shift from cows or pigs to fishes or chickens based on cost or perceived climate benefits (resulting in more animals farmed, an unfortunate phenomenon often termed small animal replacement).3
For corporate and institutional partnerships, we recommend campaigners advocate for interventions with demonstrated success in displacing animal products, such as plant-based defaults or a high proportion of plant-based to animal-based options. Strategic product placement, while effective at increasing plant-based sales, does not seem to reduce animal product purchases.4
Our confidence in this assessment is low-to-moderate due to the low number of methodologically rigorous studies and the limitations to generalizability of existing studies, and the assessment comes with several caveats. Pledges can be implemented at a low cost, have a strong logic model, and show some promise in studies using self-report and purchasing data. Therefore, we think further research is warranted, and could certainly change our mind.
Research should look into the potential of pledge campaigns in other countries (as most existing data comes from the U.K.) and into conditions that could make pledges more effective in the longer term (e.g., types of asks, increased support, and different populations).
Veg*n pledges require significant commitment and behavioral changes from individuals, so it is not surprising that those with higher starting motivation fare better at them. Pledges may therefore be a tactic particularly well suited to support individuals who are already motivated to change. Experimental studies of motivated individuals would be valuable to isolate the unique impact of the pledge.
There may also be effects of pledge campaigns on other outcomes, such as maintaining contact lists of potential supporters, raising the public profile of veg*nism, or building support for institutional campaigns. Pledges might also be a factor speeding up dietary change for already-motivated individuals or preventing veg*n recidivism. Research specifically into these effects could be valuable.
We encourage researchers to report outcomes by type of animal product reduced or replaced in order to estimate the extent of suffering averted and rule out unintended small-animal replacement effects.
In depth
What does the research say about how effective this intervention is?
Participant surveys and pre-post studies
Retrospective surveys of individuals who participated in veg*n pledges seem to suggest very high success rates in terms of a lasting dietary change; however, methodological and design limitations make it difficult to draw causal conclusions.
The yearly Veganuary six-month follow-up survey reports dramatic results. In 2023, 28% of the 6,967 survey participants reported to have transitioned to veganism in the past six months as a result of their participation, and a further 63% said they removed at least 25% of animal products from their diet, an overall success rate of 91%.5 Results from previous years are consistent. Such surveys suffer obvious limitations, such as non-response bias (response rates are low, and participants who changed their behavior may have disproportionately responded to the survey invite), limitations of retrospective self report (participants may misremember their baseline or post-intervention animal product consumption), and social desirability bias (participants may misrepresent their animal product consumption to satisfy perceived researcher expectations).
Furthermore, individuals who choose to participate in a campaign like Veganuary seem to already show more positive attitudes and behaviors toward animals than the average. One study found that the majority of pledgers in U.K. pledge campaigns were already reducing their animal product consumption at baseline.6 While this potentially limits the counterfactual impact of such pledges, they may still prevent such people from reverting back to eating more animal products. Retaining vegans and vegetarians is challenging,7 and the behavioral commitment and practical and social support associated with veg*n pledges could be significant factors in moving individuals toward the later, more stable phases of behavior change.8 As Björn Ólafsson argues,9 pledges could be the event that kickstarts or speeds up the transition process for someone already motivated to make the change. Direct evidence for the above ideas is currently lacking.
A pre-post study of 40 Veganuary participants showed that participants reported significantly higher levels of meat disgust after the campaign. Most participants lapsed into eating meat during the challenge, but disgust increases were higher the more the participants had managed to reduce their meat intake.10 This suggests that, even if meat is not fully avoided during a veg*n pledge period, the experience of reducing meat consumption could cultivate negative emotional associations with meat, although we don’t know how long these effects last.
Real-world purchasing data
Studies using real-world purchasing data show mixed, but promising, results.
In 2019, a large-scale panel survey estimated that 1.31 million British adults (4.7% of the population and significantly more than official Veganuary signups) gave up animal products in January 2019, with 832 thousand new adopters. Purchasing data of panellists engaging in Veganuary for the first time confirmed a substantial reduction in January 2019, estimated to equate to a reduction of more than 1 million kg of animal products when extrapolated to all 832 thousand first-timers.11 The researchers also found a sustained (though smaller) reduction over the following six months, estimated to equate to over 4 million kg of animal products when extrapolated to all 832 thousand first-time participants.12 This real-world purchasing data suggests that a highly prolific pledge campaign, such as Veganuary, may lead to a substantial reduction in animal product consumption that could last for at least six months, and even apply to people not officially signed up to the campaign. However, the original report was not publicly available, so we were unable to verify the estimates. It is also unclear how much of this effect can be counterfactually attributed to the Veganuary campaign.
Notably, the same researchers also report that this effect did not translate into an overall downward trend in meat, fish, or poultry sales in the U.K. in the 12 weeks leading up to the end of January 2019. In fact, there was even an increase in fish purchases during January.13 (However, it is possible that Veganuary mitigated larger increases in animal product consumption that year.) Our World in Data also reports that the proportion of meat eaters, flexitarians, vegetarians, and vegans in the U.K. has stayed largely constant between 2019 and 2025.14
Some sales data suggests that there may be a trend of decreasing interest in meat-free and dairy-free products in the U.K. during Veganuary, with over a million fewer households buying meat-free products in January 2023 compared to the previous year, and 280 thousand fewer households buying dairy-free products.15
In Germany, reductions in meat purchases in January as compared to December have increased from just over 50% in 2022 to 60% in 2024. Much of that can be attributed to increases in meat purchases in December, but compared to the 2023 average, meat purchases were still 12.5% lower in January 2024.16
Experimental studies
The few experimental studies of veg*n pledges generally show a significant reduction in meat consumption during the pledge period compared to baseline levels, but the change is usually either not sustained17 or significantly reduced18 after the intervention period. The studies that do show a sustained (albeit reduced) change tend to suffer from several methodological limitations, such as lack of a control group19 or empty control condition,20 and a very short follow-up period.21
In perhaps the most rigorous experimental test of the effectiveness of veg*n pledges to date,22 participants in Australia, Germany, and the U.K. were randomly assigned to pledge to go meat-free for 28 days, or to the no-pledge condition. During the pledge period, participants submitted daily surveys and meal photos through their smartphones to reliably track consumption. Meat consumption frequency was also measured before the pledge, immediately after, and one month after the pledge period. Daily meat consumption was reduced in pledgers relative to nonpledgers during the pledge period in all three countries, but there were no significant changes compared to baseline at the one-month follow up.
However, these general population samples may not represent typical voluntary Veganuary participants, who likely have higher intrinsic motivation. Since this motivation might be crucial for sustained change, it is difficult to generalize the experimental findings to real-world campaigns.
Meta-analyses and systematic reviews
We are not aware of any meta-analyses or systematic reviews on veg*n pledges.
Meta-analytic research from research on environment-friendly behaviors suggests that behavior change commitments have moderate effects on behavior during the intervention period as well as after (although with varying follow-up time points), but only a very small advantage over other types of behavioral change interventions, such as persuasive communication.23 It’s unlikely that these results can be generalized directly to animal product consumption, given people’s unique attachment to meat consumption.24
Other effects of pledge campaigns
Veg*n pledges can also be used for purposes that go beyond individual dietary change, such as promoting institutional campaigns. The evidence base for these tactics is again limited to Veganuary specifically, and is generally sparse, but suggests that Veganuary campaigns could be a useful advocacy tool for institutional plant-based outreach. Such promotions seem to be associated primarily with an increase in sales of plant-based products (rather than reduced sales of animal products), and there is a lack of evidence for sustained effects. It is also unclear to what extent the Veganuary brand itself contributes to these outcomes, as opposed to the influence of the modified food environment (e.g., prominent product placement or active promotions). However, the popularity of Veganuary likely contributes to successfully building these corporate partnerships in the first place.
Veganuary partners with businesses each year to increase the availability of plant-based products. In 2024, this collaboration led to hundreds of new vegan menu items and products across the U.S., U.K., Germany, Mexico, Argentina, and many other countries. In the U.S. alone, over 400 businesses were successfully engaged and launched 300 new menu items and promotions.25 Evidence suggests that increasing the proportion of plant-based relative to animal-based meals or products may positively affect plant-based sales. However, the proportion of plant-based to animal-based meals or products likely needs to be very high, and there is less clarity on the extent to which animal products are actually replaced.26
One study of U.K. supermarkets showed that using the Veganuary brand to promote plant-based products increased plant-based sales, but did not affect meat sales.27 The intervention involved increasing the availability, visibility, accessibility, and affordability of plant-based products, interventions that have been shown to, with varying success, have the potential to increase plant-based sales.28 The added value of the Veganuary branding and the campaign to coincide with Veganuary is unknown.
Similarly, a study evaluating a Veganuary promotion event in U.K. supermarkets found that, during the Veganuary promotion, sales increased for the specific plant-based foods that were on promotion (which involved prominent positioning and price reductions), but the overall sales of plant-based foods did not. The authors did not report on changes in meat sales. Effects were not sustained after the intervention period.29
Researchers also examined the impact of Veganuary promotion campaigns that increased the availability and salience (e.g., promotion, labelling) of plant-based products in U.K. workplace cafeterias. The results showed a significant increase in the proportion of vegan and vegetarian meals sold during and after the campaigns (with effects noticeable up to a year later), which suggests a corresponding decrease in the proportion of animal product purchases.30
It is certainly plausible that the Veganuary brand plays a role in the above effects, e.g., through motivating companies and institutions to take part in the first place, given how hugely popular the campaign is. Sign ups have been increasing year on year since 2015 (from 12,800 to 1.8 million in 2024),31 and more than ¾ of Brits report being aware of the campaign.32 Indeed, an expert we consulted confirmed that companies are keen to reach the Veganuary audience as potential consumers seeking plant-based alternatives.
Veganuary has likely also had a cultural impact by popularizing the concept of veganism, but we are not aware of any direct supportive evidence.
Cost effectiveness
Veg*n pledge campaigns often rely on low-cost outreach methods such as social media and email marketing and therefore seem to have the potential to be a cost effective intervention. Yet, there are significant differences between existing cost-effectiveness analyses, indicating high uncertainty.
A 2020 analysis estimates that Challenge 22, a 22-day vegan pledge, leads to a reduction by 3-40 portions of meat per $ spent over 7 months.33 However, the analysis is based on an observational survey of participants in Challenge 22,34 which shares some of the same limitations as the Veganuary follow-up survey, and we think the cost-effectiveness analysis does not sufficiently take into account the counterfactual impact, i.e., how much participants would have reduced their meat consumption without participating in Challenge 22.
A 2025 analysis in the Effective Altruism Forum estimates that the cost effectiveness of Veganuary in 2024 was 1.2% of that of cage-free corporate campaigns in terms of suffering averted relative to cost, based on the 25 million people who, according to Veganuary estimates, have taken part in Veganuary in 2024 (not limited to official sign-ups)35 as well as Veganuary’s corporate engagement activities in that year. Note that Wendy Matthews, the international head of partnerships and expansion at Veganuary, thinks this underestimates the impact of Veganuary, which she thinks goes beyond people who report having participated in the campaign.36
Another cost-effectiveness analysis of Veganuary yielded estimates ranging from 0.009 to 1.23 times the same estimate for cage-free campaigns.37
Note that, given capacity, we have not personally reviewed any of the assumptions or model inputs for these analyses. We plan to do so for future iterations of this review.
Strength of evidence
Many of the cited studies share general limitations, such as self-report of animal product consumption which may introduce biases or inaccuracies in reporting, limited sample diversity (predominantly female, left-leaning, university-educated, and from the U.K., U.S., and Europe), a lack of pre-registration or open data, and research designs that don’t allow for causal inference.
Much of the research focuses specifically on Veganuary, and it is unclear to what extent effects of Veganuary apply to other pledge campaigns given Veganuary’s outsized popularity, which may create a unique support system and social context that could amplify its positive outcomes.
Some results suggesting the strongest effects come from non-peer reviewed sources and were often commissioned by Veganuary themselves, and we would like to see more independent research following a pre-registered research and analysis plan.
Most studies discussed do not differentiate meat reduction or replacement by type of meat. Some types of meat (such as fish and poultry) are associated with much more animal suffering relative to volume than others (such as beef or pork).38 If participants selectively reduce consumption of beef or pork while maintaining or even increasing their intake of fish or chicken, then studies reporting overall meat reduction without this crucial differentiation could significantly misrepresent the actual impact on animal welfare.
Under what conditions is this intervention more or less effective?
Effects of the ask: The strongest support exists for the effect of the specific ask: Two studies suggest that a stricter ask (vegetarian or vegan) seems to be more effective than a flexitarian or reduction ask.39
Participant effects:
Participants with a stronger starting motivation40 and those who already reduce their animal product consumption prior to the pledge41 tend to show greater reductions.
The evidence is more speculative when it comes to the reasons why people adhere to vs. abandon a commitment. Some studies indirectly suggest that pledges may be more successful when alternatives to non-vegan foods are more readily available,42 and when there is more support provided during the pledge period.43
Social support: Pledges may be more effective when they involve social support. Specifically, a study into the Veggie Challenge found that both those participating individually and those encouraged to involve their friends and family reduced their animal product consumption by 16-17% relative to a control group, but only the social encouragement group showed a lasting reduction three months after the pledge period.44
Small animal replacement: There may be a risk of small animal replacement, whereby participants replace the consumption of lower-suffering animals (such as cows or pigs) with higher-suffering animals (such as fishes or chickens), which may be perceived as less harmful and better for the climate, and is also often cheaper.45
Our priorities for improving this evidence review
For future versions of this evidence review, we would like to explore in more detail how veg*n pledges could serve as tactics to generate momentum for other campaigns or to gain more supporters or donors, e.g., by talking to advocates and topic experts.
We would also like to explore other outcomes of veg*n pledges that could benefit animals in the longer term, such as improving public perceptions of veg*nism or raising awareness of plant-based alternatives.
We plan on reviewing the studies that report reduction separately for different types of animal products to gauge whether pledges are overall more likely to reduce some types of animal products than others, with a specific focus on the amount of suffering involved in their production.
We would like to critically assess the cost-effectiveness analyses and their assumptions in more depth.
We plan to solicit internal impact data from organizations using veg*n pledges.
We would like to thank Björn Ólafsson and Prashanth Vishwanath for their helpful feedback as peer reviewers.
However, participants who felt particularly negatively about the challenge may also be disproportionately likely to respond.
See, e.g., Rothgerber, 2019
See our evidence review on Corporate and Institutional Veg*n Outreach
See also Bryant et al. (2022)
Note that the measurement excluded processed foods and out-of-home consumption.
Kantar, as reported by Veganuary (2020)
YouGov, as reported by Our World in Data (2025)
Lindemann-Matthies et al. (2023)
Dakin et al. (2021); Lindemann-Matthies et al. (2023)
See our evidence review on Corporate and Institutional Veg*n Outreach
See our evidence review on Corporate and Institutional Veg*n Outreach
Dakin et al. (2021); Grassian (2020)
Piazza et al. (2022); Veganuary (2023)
Lindemann-Matthies et al. (2023); Grassian (2020)
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