Study Finds Plant-Forward Diets Reduce Carbon Footprints and Improve Diet Quality

A 2021 United Nations-backed study found that 34% of greenhouse gas emissions come from the food system, with beef being responsible for 8-10 times more emissions than chicken production and over 20 times more emissions than nut and legume production.^[0] In an effort to measure the carbon footprints of U.S. diets and compare them to other common diets, researchers at Tulane University recently published a study in The American Journal of Clinical Nutrition.^[1]

The study, “Popular diets as selected by adults in the United States show wide variation in carbon footprints and diet quality,” compiled diet quality scores using data from more than 16,000 adult diets collected by the Centers for Disease Control and Prevention’s National Health and Nutrition Examination Survey.^[2] Points were assigned to each individual diet based on the federal Healthy Eating Index, and the average score for those consuming each type of diet was computed.^[3]

On the lower end of the scale, the analysis revealed that the keto diet, which prioritizes high amounts of fats and low amounts of carbs, and the paleo diet, which eschews beans and grains in favor of meats, nuts, and vegetables, scored among the lowest on overall nutrition quality and were among the highest on carbon emissions (with 3kg and 2.6kg of CO2 for every 1,000 calories consumed, respectively).^[4]

The vegan diet was found to be the least impactful to the environment, generating only 0.7kg of CO2 per 1,000 calories consumed, followed by vegetarian and pescatarian diets. Vegetarian and vegan diets had the second highest nutritional quality scores, with the former scoring the highest.

It was interesting to note that the nutritional quality of pescatarian diets was the highest, surpassing both vegetarian and vegan diets. Furthermore, omnivores who followed a Mediterranean diet — which calls for a colorful mix of vegetables, fruits, whole grains, healthy fats, and lean protein — were ranked higher on nutritional quality and had smaller carbon footprints compared to others in the group. The same was true for the DASH diet, a heart-healthy plan that limits red meat consumption.^[5]

Of note, when those who follow omnivorous diets select the plant-based Mediterranean or the fatty meat-restricting DASH diet, both the carbon footprints and nutrition scores improve.

0. “Keto vs vegan: Study of popular diets finds over fourfold difference in carbon footprints” Anti Aging News, 3 Mar. 2023, https://www.worldhealth.net/news/keto-vs-vegan-study-popular-diets-finds-over-fourfold-difference-carbon-footprints/

1. “Study estimates the carbon footprint and diet quality of popular U.S. diets” News-Medical.Net, 3 Mar. 2023, https://www.news-medical.net/news/20230302/Study-estimates-the-carbon-footprint-and-diet-quality-of-popular-US-diets.aspx

2. “From Vegan to Keto, Which of 6 Popular Diets Has the Highest Carbon Footprint?” Treehugger, 3 Mar. 2023, https://www.treehugger.com/vegan-to-keto-diet-highest-carbon-footprint-7182330

3. “These trendy diets are the least healthy way to lose weight” coastalbreezenews.com, 2 Mar. 2023, https://www.coastalbreezenews.com/news/national/these-trendy-diets-are-the-least-healthy-way-to-lose-weight/article_bcbda154-9886-5ec4-a1d4-f372484df04a.html

4. “Study reveals the environmental impacts of various diets” Earth.com, 1 Mar. 2023, https://www.earth.com/news/study-reveals-the-environmental-impacts-of-various-diets/

5. “How the keto diet compares to greener eating, in two charts” Insider, 3 Mar. 2023, https://www.insider.com/how-the-keto-diet-compares-to-greener-eating-two-charts-2023-3