Wednesday, July 17, 2024

Vegan Diets have less than half the Environmental Impact of High-Meat Diets

A scientific study has found that vegan diets have a much lower environmental impact than meat-based diets, especially those containing at least 100 grams of meat per day.

The researchers, mostly based at the University of Oxford, linked dietary data from 55,504 volunteers living in the UK with a comprehensive database of the environmental impacts of different foods based on data from more than 38,000 farms spread across 119 countries. Volunteers completed a 130-item dietary questionnaire and their reported food intakes were used to estimate five measures of the environmental impact of their diet: greenhouse gas emissions, land use, water use, eutrophication potential (a measure of water pollution), and the impact on biodiversity (a measure of the variety and variability of life on Earth). Greenhouse gas emissions were estimated separately for carbon dioxide [CO2], methane [CH4] and nitrous oxide [N2O], and combined as carbon-dioxide equivalents [CO2e] according to their 100-year global warming potential.

The volunteers were divided into six diet groups: vegans (who did not eat any meat, fish, dairy products or eggs), vegetarians (who did not eat meat or fish but did eat dairy products and/or eggs), fish-eaters (who did not eat meat but did eat fish), and low, medium or high meat-eaters according to whether they ate less than 50, 50-99 or at least 100 grams of meat per day. (For example, 50 grams of meat might be two slices of ham, whereas 100 grams might be a small steak.) Environmental impacts for each volunteer’s diet were calculated and standardised to a 2000 kcal/day diet and by age and gender to allow for differences in characteristics between the diet groups (for example, of the six diet groups the vegans had the lowest average age and food energy intake, and the lowest percentage of women volunteers). This process was repeated across 1000 simulations to allow for variations in the estimated impacts of each food according to different methods of production (for example, beef from grass-fed cattle in the UK has a different impact to beef from intensively reared cattle in Brazil), and the results were aggregated to calculate median environmental impacts by diet group, together with 95% uncertainty intervals. (The median is the midpoint or 50 percentile of a set of values, while the 95% uncertainty interval stretches from the 2.5 percentile to the 97.5 percentile, excluding only the lowest and the highest 2.5% of values.) Graphs were used to show proportional environmental impacts by diet group relative to high meat-eaters, together with their 95% uncertainty intervals.

All five measures of dietary environmental impact, and each of the separate estimates of greenhouse gas emissions, showed a clear gradient of impact from vegans (lowest impact), through vegetarians (next lowest impact), fish eaters, low and medium meat-eaters to high meat-eaters (highest impact). (The sole exception was for water use, for which fish-eaters and low meat-eaters had the same median impact.) For example, median dietary CO2 emissions ranged from 2.16 kg/day for vegans to 7.28 kg/day for high meat-eaters. Emissions of all three greenhouse gases for vegan diets were, on average, less than one-third of those for high meat-eaters, as shown in the graph below (the black squares represent the median impact relative to high meat-eaters, with the horizontal lines showing the 95% uncertainty intervals).

On average, the environmental impact of vegan diets was just one-quarter (25%) that of high meat-eaters for each of combined greenhouse gas emissions (CO2e) and land use, and less than half as much for water use (46%), eutrophication potential (27%), and biodiversity (34%), as shown in the graph below. In every case, the 95% uncertainty interval for vegans is well below one, indicating a high level of confidence that the differences in environmental impact between vegan diets and high meat-eater diets are genuine.

Smaller differences in impact were seen for vegetarians compared with high meat-eaters, and even low meat diets had about half the impact of high meat-diets for each of combined greenhouse gas emissions, land use and water pollution. As lead researcher, Prof Peter Scarborough pointed out: “Our dietary choices have a big impact on the planet. Cutting down the amount of meat and dairy in your diet can make a big difference to your dietary footprint.” However, as this study has shown, vegan diets lead the way when it comes to reducing the environmental impact of your diet.

Sources and links:

Paul Appleby is a Fellow of the UK Vegetarian Society and a former trustee of the Society and the UK Vegan Society.  He was secretary of Oxford Vegetarians (the forerunner of OxVeg) for 25 years from 1983 to 2008.  Until he retired in 2020, Paul was a Senior Statistician at the Cancer Epidemiology Unit, University of Oxford, working mainly on long-term studies of the health of vegetarians and vegans, including the EPIC-Oxford study.


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