Keto, paleo, vegetarian, pescatarian, vegan… in the last few years, approaches to eating that favour or eliminate the consumption of one or more foods have become commonplace. But how do they stack up in terms of their carbon footprint?
Researchers from Tulane University in New Orleans set out to provide a comprehensive answer to this question. They looked at data collected in a national survey by the US Centers for Disease Control and Prevention, consisting of the nutritional scores of more than 16,000 diets.
Average daily greenhouse-gas emissions in kilogrammes of carbon-dioxide equivalents per 1,000 kcal (kg CO2-eq/1,000 kcal) were calculated for each diet studied.
“Diet quality” was determined using various healthy eating indices, and once these diets were assessed, the researchers established a ranking from the most to the least polluting.
The keto diet, which is based around consuming fats in large quantities and carbohydrates in small quantities, generates nearly 3kg of carbon dioxide for every 1,000 calories consumed. This diet was, therefore, found to be the least environmentally friendly.
It was followed by the paleo diet, which gives pride of place to proteins and plants but which bans certain foods such as cereals and dairy products. In terms of impact on the planet, its score is estimated at 2.6kg CO2-eq per 1,000 kcal.
The omnivore diet – adopted by 86% of the participants in the survey – is estimated to generate 2.23kg CO2-eq per 1,000 kcal.
Unsurprisingly, the vegan diet was found to be the least polluting of all: 0.7kg of carbon dioxide per 1,000 calories consumed, less than a quarter of the impact of the ketogenic diet.
Finally, the vegetarian diet was found to generate 1.16 kg CO2-eq per 1,000 kcal.
“Our results highlight the nuances when evaluating the nutritional quality of diets and their carbon footprint,” the researchers concluded.
“On average, pescatarian diets may be the healthiest, but plant-based diets have lower carbon footprints than other popular diets, including keto and paleo.”