Sustainability of Healthy and Unhealthy Diets22 June 2013
Healthier diets are not necessarily more sustainable than unhealthy diets according to a French study.
However, the conclusions have been challenged by the Food Climate Research Network, which claims the results have been misinterpreted.
The conclusions of the report says that 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 GHG emissions.
The report, High nutritional quality is not associated with low greenhouse gas emissions in self-selected diets of French adults, by F. Vieux, L-G Soler, D. Touazi and N Darmon, says that 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.
The study went on to estimate the GHGEs associated with the consumption of self-selected diets in France and to analyse their relation with the nutritional quality of diets.
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.
The study says the mean adequacy ratio was positively correlated and mean excess ration was negatively correlated with diet-related GHGEs.
It found that 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.
However, the Food Climate Research Network said that 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 lower in the case of women, the FCRN said.
It added that higher quality diets tend to 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,” the FCRN said.
“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 freshly pressed, chilled exotic juices. It is also possible to have a 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.”