Not all diets they are equal, as regards the nutritional value and the impact on the planet of what you decide to eat. And the two types of evaluation do not always coincide. Sometimes, what we think is good for health has a non-negligible environmental impact and it would therefore be appropriate to be aware of it. Conversely, many people who, without having consulted a doctor or nutritionist, thinking of losing weight or improving their health decide to opt for a diet that specifically gives more or less space to a certain type of nutrient such as proteins, carbohydrates or plant foods, they are not at all concerned with the environmental consequences of the choice, even if perhaps they are worried about the climate crisis and think it is right to act on an individual level as well. Given that, according to the latest WHO estimates, more than a third of greenhouse gas emissions derive directly from food production and that the values vary greatly from one food to another (beef ’emits’ 8-10 times more than that of chicken and 20 times compared to plant foods), it would be appropriate to increase everyone’s level of awareness on both fronts, to help make choices that, as far as possible, keep the two instances together.
It can be useful a study just published onAmerican Journal of Clinical Nutrition, by researchers at Tulane University in New Orleans, who scanned the eating habits of over 16,000 participants in the large US population study NHANES, dividing them into six main groups: vegans, vegetarians, pescetarians, omnivores, followers of the paleo diet or the ketogenic diet. They then assigned a CO value to each of the categories2 emitted for every thousand calories and the result was very clear: there is an enormous difference between diets with a smaller footprint and those associated with more emissions: the former ’emit’ a quarter of the latter.
Indeed, the ketogenic diet, very popular and based on animal proteins, fats and very few sugars, ‘produces’ 3 kg of CO2 every 1,000 calories, and the Paleolithic one, which also allows dried fruit and vegetables, but avoiding legumes and cereals, ’emits’ 2.6 and is slightly better. Neither of them can compete with the vegan one, whose emissions are 0.7 kg/1,000 calories, which is less than a quarter of the ketogenic one. The vegetarian diet follows, with 1.16 kg/1,000, and the pescetarian diet, with 1.66 kg/1,000, which confirm themselves as an alternative. The omnivorous diet is instead associated with 2.23 kg of CO2 every 1,000 calories, but its impact can vary a lot, depending on your habits.
In addition to the environmental classification, the researchers assigned a score to the six regimes according to an international index which defines their nutritional value and in that context the result only partially coincided with the environmental one. The maximum score was obtained by the pescetarians, with 58 points, followed by vegetarians (51.8) and vegans (51.6), while paleo and keto placed themselves at a distance, with 45 and 43 respectively, and omnivores a half, with 48.
The definition of these rankings, the authors then explained, it is not so relevant in itself, but it can help people understand whether, even if they do not give up entire categories of food such as meat, but only by introducing some changes in their habits, the quality can be significantly improved of the diet and, at the same time, decrease the impact on emissions associated with food. In other words, it is a question of meeting the needs and habits of that 86% of the participants who declare themselves omnivorous, proposing them goals that are not only achievable, but also such that they can be maintained and further improved over time. From this point of view, they concluded, a good compromise is, for example, a Mediterranean diet with lots of fish.
If instead there were drastic changesthe effect would be striking: if a third of omnivores switched to a strictly vegetarian diet, it would be like eliminating 340 million km traveled by vehicles with fuel engines and also health (especially for vegetarians who do not exclude important categories such as milk and derivatives) would undoubtedly benefit from it.
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Agnes Codignola – March 13, 2023