This paper has been widely reported – and also misinterpreted. It has been publicised as a study which suggests that healthier diets (which seems to be conflated with one containing lower levels of meat and dairy) do not necessarily lead to reduced GHG emissions; however, a closer reading of the conclusions reveals otherwise.
As far as I can see high and low quality nutritional diets differ hardly at all in their meat and dairy content. Dairy consumption among women consuming higher quality diets tends to be higher (slightly lower for men), pork, poultry and eggs more or less the same, and for ruminant meat, intakes are very slightly lower among high quality consuming men and very slightly higher in the case of women.
Higher quality diets tend to be be richer in fruit and vegetables which substitute for the sweets and carbohydrates eaten by those with poor diets. Lower quality diets contain more sweets and carbohydrates relative to fruits and vegetables and therefore their GHG emissions tend to be lower. This is hardly surprising – carbohydrates per calorie are bound to have a lower GHG footprint. This is, after all, why wheat and maize are grown as biofuels and not broccoli and apples. To emphasise – the issues are with vegetables substituting for refined carbohydrates and not with their substituting for animal products.
It is no surprise that you can have a healthy unsustainable diet – and indeed a healthy unsustainable vegan diet - eg. think airfreighted fruits and vegetables, large quantities of toand freshly pressed, chilled exotic juices. It is also possible to have an healthy sustainable diet containing some (although not large quantities ) of meat and dairy foods – it’s about the balance and what is consumed in place of / in addition to animal products.
Background: Healthy diets are supposed to be more environmentally friendly because they rely mainly on plant-based foods, which have lower greenhouse gas emissions (GHGEs) per unit weight than do animal-based foods.
Objectives: The objectives were to estimate the GHGEs associated with the consumption of self-selected diets in France and to analyze their relation with the nutritional quality of diets.
Design: For each adult in the national dietary Individual and National Survey on Food Consumption (n = 1918), the GHGEs of his or her diet were estimated based on the GHGEs of 391 foods. Highest nutritional- quality diets were defined as those having simultaneously 1) an energy density below the median, 2) a mean adequacy ratio (MAR) above the median, and 3) a mean excess ratio (MER, percentage of maximum recommended values for nutrients for which intake should be limited) below the median.
Results: MAR was positively correlated and MER was negatively correlated with diet-related GHGEs. High-nutritional-quality diets contained more plant-based foods, notably fruit and vegetables, and fewer sweets and salted snacks than did low-quality diets. After adjustment for age, sex, and energy intake, the consumption of sweets and salted snacks was negatively correlated with diet-related GHGEs, whereas the consumption of animal products and of fruit and vegetables was positively associated with them. After adjustment for energy intake, high-nutritional-quality diets had significantly higher GHGEs (+9% and +22% for men and women, respectively) than did low nutritional-quality diets.
Conclusion: Despite containing large amounts of plant-based foods, self-selected diets of the highest nutritional quality are currently not those with the lowest diet-related GHGEs
You can download the paper here (journal access needed).
Vieux F, Soler L-G, Touazi D and Darmon N (2013). High nutritional quality is not associated with low greenhouse gas emissions in self-selected diets of French adults, Am J Clin Nutr; 97: 569–83