On Friday, May 8, the public comment period closed for the new 2015 Dietary Guidelines issued by the U.S. Department of Agriculture (USDA) and the Department of Health and Human Services (HHS). In a nutshell, the new dietary guidelines are to eat a diet richer in plant-based foods and leaner in animal-based products. One of the considerations used by the USDA/HHA in their Scientific Report used to rationalize these new dietary guidelines was that such diets are

“associated with more favorable environmental outcomes (lower greenhouse gas emissions and more favorable land, water, and energy use) than are current U.S. dietary patterns.” [emphasis added]

Throughout the Scientific Report whenever greenhouse gases are mentioned, a negative connotation is attached and food choices are praised if they lead to reduced emissions.

This is misleading on two fronts. First, the dominant greenhouse gas emitted by human activities is carbon dioxide which is a plant fertilizer whose increasing atmospheric concentrations have led to more productive plants, increasing total crop yields by some 10-15 percent to date. The USDA/HHS is at odds with itself in casting a positive light on actions that are geared towards lessening a beneficial outcome for plants, while at the same time espousing a more plant-based diet.

And second, the impact that food choices have on greenhouse gas emissions is vanishingly small—especially when cast in terms of climate change. And yet it is in this context that the discussion of GHGs is included in the Scientific Report. The USDA/HHS elevates the import of GHG emissions as a consideration in dietary choice far and above the level of its actual impact.

In our Comment to the USDA/HHS, we attempted to set them straight on these issues.

Our full Comment is available here, but for those looking for a synopsis, here is the abstract:

There are really only two reasons to discuss greenhouse gas emissions (primarily carbon dioxide) in the context of dietary guidelines in the U.S., and yet the USDA and HHS did neither in their Scientific Report of the 2015 Dietary Guidelines Advisory Committee (DGAC).

The first reason would be to discuss how the rising atmospheric concentration of CO₂—a result primarily of the burning of fossil fuels to produce energy—is a growing benefit to plant life. This is an appropriate discussion in a dietary context as atmospheric CO₂ is a fertilizer that promotes healthier, more productive plants, including crops used directly as food for humans or indirectly as animal feed. It has been estimated that from the atmospheric CO₂ enrichment to date, total crop production as increased by 10-15 percent. This is a positive and beneficial outcome and one that most certainly should be included in any discussion of the role of greenhouse gases emissions in diet and nutrition—but is inexplicably lacking from such discussion in the DGAC report.

The second reason to discuss greenhouse gas emissions in a diet and nutrition report would be to dispel the notion that through your choice of food you can “do something” about climate change.  In this context, it would be appropriate to provide a quantitative example of how the dietary changes recommended by the DGAC would potentially impact projections of the future course of the climate. Again, the DGAC failed to do this.  We help fill this oversight with straightforward calculation of averted global warming that assumes all Americans cut meat out of their diet and become vegetarians—an action that, according to the studies cited by the DGAC, would have the maximum possible impact on reducing greenhouse gas emissions and thus mitigating future climate change.  Even assuming such an unlikely occurrence, the amount of global warming that would be averted works out to 0.01°C (one hundredth of a degree) by the end of the 21^st century.  Such an inconsequential outcome has no tangible implications.  This should be expressed by the DGAC and mention of making dietary changes in the name of climate change must be summarily deleted.

We recommend that if the DGAC insists on including a discussion of greenhouse gas emissions (and thus climate change) in it 2015 Dietary Guidelines, that the current discussion be supplemented, or preferably replaced, with a more accurate and applicable one—one that indicates that carbon dioxide has widespread and near-universal positive benefits on the supply of food we eat, and that attempting to limit future climate change through dietary choice is misguided and unproductive.  These changes must be made prior to the issuance of the final guidelines. 

We can only guess on what sort of impact our Comment will have, but we can at least say we tried.