Dietary health and global warming: these are two major societal issues finding a lot of media time lately. Diabetes is on the rise, with a third of the US population projected to have diabetes by 2050. After a low-fat diet fad for several decades, sugars and carbohydrates are now the enemy. Different vegetables are touted each week as the newest cancer fighter and Cheerios still advertises as being good for heart health. If the media is an indication, we as a people eat up, if you will, all the food information we can get to try to keep eating better.
And then there’s global warming. Greenhouse gas emissions (GHG) leading to 2-6 degrees Celsius increases in global mean temperature by the end of the century, sea level rises, coastal habitats threatened – we’ve heard the predictions plenty. Skeptics abound and the media grabs at the opportunity for every kind of point-counterpoint you can imagine.
These two issues seem separate, but a new research study in the Journal of Industrial Ecology indicates that they’re linked. Unfortunately, the results suggest that the nation following USDA dietary recommendations would lead to a net increase in greenhouse gas emission. Another piece of evidence of how interconnected the world truly is, and how our individual actions do make a difference once summed over the global population.
Food production is already a major factor in total greenhouse gas emissions. Direct emissions from agriculture plus fertilizer and fuel lead to 17-32% of all emissions! But diet can also matter, since what we eat determines what food is grown, and we’ve already seen that meat-based diets are more CO2-intensive. Also, although cars and utilities usually account for most greenhouse gas emissions per household, diet changes may be the most economically feasible for reducing personal emissions.To see how diet affects emissions, Heller and Keoleian tracked the USDA’s Loss Adjusted Food Availability (LAFA) data, which basically tracks what food vanishes into the US food market as we all buy and eat it, after adjusting for losses that occur along the way (e.g., waste, nonedible portions, etc.). They then combined this series with their own meta-analysis of the literature on the CO2 footprint for each food type. Thus, they had a CO2 value for each food type, which they could then use to determine the total CO2 footprint for a given type of diet.
So what are we currently eating and what’s recommended? This concise graph lays it all out:This shows the relative percentage increase or decrease that would need to be made from the average US diet to meet standard USDA recommendations (for either a 2000 or 2534 calorie diet). So, for example, we need to increase fruit intake by 150% – that’s 3x as many servings as the average American is eating (this is a bit disheartening…). And we need to eat less meat, poultry, eggs, nuts, soy, oils, and fat (that’s the SoFAS category).
Here’s the surprising pattern – below is the graph showing how GHG emissions would change if we adjusted to dietary recommendations:Notice that emissions go up if we follow the recommendations for the 2534 calorie diet (cumulative change at very bottom)! This is a 12% increase – fairly sizable. Following the 2000 calorie diet, GHG emissions reduce by about 2%. This seems to go against the previous evidence that eating a more vegetarian diet would reduce emissions. Indeed, this graph shows that following dietary recommendations would lead to less GHG emissions from meat and poultry products, but apparently this is more than made up for by eating more fruits and vegetables and, in particular, more dairy (see the large increase from current consumption in black to the guidelines).
So the main reason for these results appears to be that the calories lost from eating less meat are made up for by eating more dairy, which requires cows, which leads to much more greenhouse gas emissions. This is crucial information for the USDA – environmental impacts of recommended diets need to be taken into consideration. I think there should be a way to get the calories and nutrients from an equivalent source other than dairy, and then we could see a considerable decrease in GHG emissions from a less meat-based diets. But this is cool research – I always like to see results that indicate we need to be more aware about how even our most routine of actions – shopping and eating – affect the world around us.
Heller, M., & Keoleian, G. (2014). Greenhouse Gas Emission Estimates of U.S. Dietary Choices and Food Loss Journal of Industrial Ecology DOI: 10.1111/jiec.12174