Does consuming lettuce produce three times more emissions than bacon?

By January 23, 2025 Environment

We came across a post on X that claims that consuming lettuce produces three times more greenhouse gases (GHG) than bacon. This claim references a study by Carnegie Mellon University, which claims that the production of fruits and vegetables in the United States utilises more resources per calorie than the production of red meat.

Food production has been linked to about a third of all human-induced GHG emissions and livestock alone accounts for about 12 per cent of all human-induced GHG emissions. This has led to the widely accepted view that switching to a diet less reliant on red meat could reduce GHG emissions significantly. However, the claim that lettuce produces three times more emissions than bacon contradicts this understanding.

Additionally, in Singapore, food security is a key concern due to the country’s heavy reliance on imports. With over 90 per cent of food brought in from overseas, the environmental impact of different foods is shaped not only by production methods but also by transportation and supply chain emissions. Understanding the true carbon footprint of dietary choices is crucial as Singapore works towards sustainability goals, including its “30 by 30″ initiative to produce 30 per cent of the country’s food supply locally by 2030.

Hence, we took a closer look at the claim and study cited.

Research by Carnegie Mellon University

The 2015 study titled “Energy use, blue water footprint, and greenhouse gas emissions for current food consumption patterns and dietary recommendations in the US” was conducted by researchers from Carnegie Mellon University, a private research university in Pennsylvania, United States.

The study aimed to assess the environmental impact of adopting the 2010 US Department of Agriculture (USDA) Dietary Guidelines, which highlights balancing caloric intake to manage a healthy weight and increasing the consumption of nutrient-rich foods such as fruits and vegetables.

Using life cycle assessment studies – which evaluates a product’s environmental impact from production to disposal – the researchers assessed energy use, freshwater consumption, and GHG emissions associated with dietary changes. They compared three scenarios: (1) reducing overall food intake, (2) adopting a USDA-recommended diet without reducing calories, and (3) combining a healthier diet with lower caloric intake.

According to the researchers, to ensure a fair comparison across food types, they measured environmental impact per calorie consumed, rather than per kilogram or serving size. This approach allowed them to estimate the true impact of dietary changes, since different foods vary significantly in calorie density.

Their findings revealed that while reducing caloric intake alone decreased environmental impact, shifting to the USDA-recommended diet—even with calorie reduction—led to increased energy use, water consumption, and emissions. Specifically, adopting the USDA diet without calorie reduction resulted in 43% more energy use, 16% higher water consumption, and an 11% rise in GHG emissions, while the combined approach still led to notable increases in resource use.

Reflecting on their findings, the researchers highlighted the challenge of balancing public health goals with environmental sustainability, suggesting that future dietary recommendations should integrate both nutritional and ecological considerations.

These results suggest that while reducing caloric intake alone can lessen environmental impacts, shifting to the USDA-recommended food patterns—particularly with higher consumption of fruits, vegetables, and seafood—may lead to increased resource use and emissions due to their relatively high environmental costs per calorie.

Room for misinterpretation?

The key point of contention lies in how the study calculates environmental impact per calorie rather than per kilogram, per serving, or per nutrient profile. This means that foods with low calorie density, like lettuce, may appear to have a higher environmental impact per calorie than high-calorie foods like bacon.

However, this does not mean that bacon is inherently better for the environment than lettuce. In reality, people consume vastly different quantities of these foods. For instance, Tech Insider postulates that a person would need to eat more than 14 cups of lettuce to match the calories in a single slice of bacon. This makes per-calorie comparisons misleading when applied to individual food items.

Image via: Tech Insider

Additionally, these misleading claims often overlook the broader life cycle impact of livestock production, including feed production, land use, methane emissions, and deforestation, all of which make animal products like bacon far more resource-intensive than vegetable products like lettuce.

 

Is bacon better for the environment than lettuce?

The study’s methodology, based on per-calorie impact, is useful for understanding dietary shifts but does not mean that individual high-calorie foods like bacon are better for the environment than low-calorie foods like lettuce.

A more accurate way to compare environmental impacts would be to measure it per kilogram of food produced or per serving rather than per calorie and to assess people’s diets as a whole.

According to a 2019 study by the Agency for Science, Technology and Research (A*Star) and financial advisory firm Deloitte, pork is the largest contributor to food-related greenhouse gas emissions per capita in Singapore, accounting for roughly 28 per cent of the nation’s total food emissions. This is primarily due to Singapore’s higher per capita consumption of pork compared to other red meats and the need to import it.

The study also found that if Singapore’s 30 by 30 target is met, per capita greenhouse gas emissions could decrease by 3 per cent compared to current projections without intervention. This reduction would result from decreased reliance on food imports and the potential use of cleaner energy in local production.

However, overall emissions may still rise due to population growth, highlighting the need for additional measures to reduce the environmental impact of food consumption. One such approach is shifting towards a diet with less traditional meat and more plant-based alternatives, fruits, and vegetables, which could significantly lower food-related greenhouse gas emissions, as plant-based foods generally have a smaller environmental footprint than animal products.

Hence, we rate the claim that lettuce causes three times more emissions than bacon as false and misleading. Certain commentators and social media users have amplified this misrepresentation to discredit plant-based diets and downplay the environmental impact of excessive meat consumption.

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