Meat-Free Day Reduces Greenhouse Gas Emissions but Poses Challenges for Customer Retention and Adherence to Dietary Guidelines

Abstract

Reducing meat consumption is crucial for achieving global environmental and nutritional targets. Meat-Free Day (MFD) is a widely adopted strategy to address this challenge by encouraging plant-based diets through the removal of animal-based meals. We assessed the environmental, behavioral, and nutritional impacts of MFD by implementing 67 MFDs over 18 months (once a week on a randomly chosen day) across 12 cafeterias on a large university campus, analyzing over 400,000 food purchases. MFD reduced on-campus food-related greenhouse gas (GHG) emissions on treated days by 52.9% and contributed to improved fiber (+26.9%) and cholesterol (-4.5%) consumption without altering caloric intake. These nutritional benefits were, however, accompanied by a 27.6% decrease in protein intake and a 34.2% increase in sugar consumption. Moreover, the increase in plant-based meals did not carry over to subsequent days, as evidenced by a 3.5% rebound in animal-based meal consumption on days immediately following treated days. MFD also led to a 16.8% drop in on-campus meal sales on treated days.Monte Carlo simulations suggest that if 8.7% of diners were to eat burgers off-campus on treated days, MFD's GHG savings would be fully negated. As our analysis identifies on-campus customer retention as the main challenge to MFD effectiveness, we recommend combining MFD with customer retention interventions to ensure environmental and nutritional benefits.

Figures (7)

• Figure 1: Analysis setups to estimate the effect of Meat-Free Day (MFD).(a) on-MFD Analysis: This setup examines the direct impact of MFD on three key outcomes: greenhouse gas (GHG) emissions (RQ1), sales patterns (RQ2), and nutrient intake (RQ3). Each MFD (randomly assigned to a weekday in week $t+1$) is matched with a corresponding non-MFD from the preceding week $t$, occurring on the same weekday. This comparison quantifies the immediate effect $\Delta$ on these outcomes. (b) beyond-MFD Analysis: This setup investigates potential rebound effects by analyzing consumer behavior on the day following an MFD. A non-MFD in week $t+1$ that occurs immediately after week $t+1$'s MFD is matched with a non-MFD from week $t$ that occurs on the same weekday, but at least two days after week $t$'s MFD. This comparison assesses whether MFD triggers compensatory behaviors that could counteract its intended effects.
• Figure 2: Impact of Meat-Free Days (MFD) on greenhouse gas (GHG) emissions and on-campus meal sales.(a) GHG emissions: Average monthly GHG emissions on MFDs (blue) compared to matched non-MFDs (orange). We observe a consistent and significant reduction in GHG emissions throughout the study period, with an overall decrease of 5,053 kgCO$_2$e/day ($p<0.001$), corresponding to a relative reduction of 52.9%. (b) Sales: Average monthly on-campus meal sales on MFDs (blue) compared to non-MFDs (orange). Meal sales significantly decreased by an average of 16.8% ($p<0.001$) on MFDs, suggesting increased off-campus dining and potential offsetting of on-campus emission savings.
• Figure 3: Impact of off-campus dining on GHG emission savings. Results from Monte Carlo simulations accounting for variability in the proportion of fast-food customers (x-axis). The x-axis represents the expected proportion of fast-food customers, computed as the mean $\alpha / (\alpha + \beta)$ of a Beta distribution where $\alpha$ and $\beta$ represent the assumed number of fast-food and non-fast-food customers, respectively. The y-axis shows the percentage offset in GHG due to off-campus dining. In the best-case scenario, where no off-campus customers visit fast-food restaurants, the offset effect reaches 58.7%. The average offset is not statistically different from the break-even point (red line) at 40% (95% CI [82.2%, 106.1%]). On average, the break-even point is reached at 50.2% fast-food proportion, beyond which the offset exceeds the emissions savings from MFD.
• Figure 4: Impact of Meat-Free Day (MFD) on caloric and macronutrient intake. Average intake of calories and macronutrients on MFDs and non-MFDs (x-axis) compared to recommended guidelines (gray boxes). Calories are measured in kcal and scaled by a factor of 100, whereas carbohydrates are scaled by a factor of 10 to align with the visualization of error bars for other macronutrients. This figure shows the diverse impact of MFD on nutrition: while it preserves caloric intake and it improves fiber and cholesterol consumption, there are risk due to lower protein and higher carbohydrate intake.
• Figure 5: Changes in sales of unhealthy food items on Meat-Free Days (MFDs). Percentage daily changes in sales for vending machine items, energy and sugary drinks, pastries and snacks, and desserts on MFDs relative to non-MFDs. No significant differences were observed for vending machine items, energy and sugary drinks, or pastries and snacks. However, dessert sales increased by 15.9% ($p<0.001$), corresponding to an additional 27 desserts sold compared to a baseline of 167 desserts on non-MFDs. This increase suggests a potential compensatory behavior driven by the perception that vegetarian meals are less nutritionally adequate.