Controversy over the new dietary guidelines

Yesterday I filmed a piece on Fox Business about the new dietary recommendations and the call to reduce meat consumption to improve health and the environment (I couldn't get the video to embed, but you can view it here).  I suppose I had at least a couple good points to make because the clip was featured for most of yesterday on the main web page for Fox News.  

One of the hosts mentioned a Cambridge study showing that vegetarians and vegans have substantially lower environmental impacts than meat-eating diets.  A written piece at about the recommendations also mentions the same study.  I'm not sure how representative that cited study is.  My own analysis suggests that vegetarians spend about the same amount on food as do meat eaters.  To the extent prices reflect resource use, that stat would suggest both diets are "using up" similar levels of "stuff."  I've also written on the argument that the grain fed to livestock is "wasted."

But, perhaps more importantly, what evidence is cited in the new report of the dietary guidelines committee?  The papers they cite seem to suggest small improvements in greenhouse gas (GHG) emissions and improved health outcomes (but more on that in a minute) from a move to vegetarian diet.  Here are some selected quotes of the review in Chapter 5 part D where quantitative impacts on environment were mentioned (note: there are many other cited studies, some of which suggest higher impacts).

Peters et al. examined 42 different dietary patterns and land use in New York, with patterns ranging from low-fat, lacto-ovo vegetarian diets to high fat, meat-rich omnivorous diets . . . although meat increased land requirements, diets including meat could feed more people than some higher fat vegetarian-style diets


Aston et al. assessed a pattern that was modeled on a feasible UK population in which the proportion of vegetarians in the survey was doubled, and the remainder adopted a diet pattern consistent with the lowest category of red and processed meat (RPM) consumers. They found . . . the expected reduction in GHG for this diet was ~3 percent of current total carbon dioxide (CO2) emissions for agriculture. De Carvalho et al. also examined a high RPM dietary pattern with diet quality assessed using the Brazilian Healthy Eating Index.They found . . . that excessive meat intake was associated not only with poorer diet quality but also with increased projected GHG emissions (~ 4 percent total CO2 emitted by agriculture).

This one is most interesting references:

a report from Heller and Keoleian suggests that an isocaloric shift from the average U.S. diet (at current U.S. per capita intake of 2,534 kcals/day from Loss-Adjusted Food Availability (LAFA) data) to a pattern that adheres to the 2010 Dietary Guidelines for Americans would result in a 12 percent increase in diet-related GHG emissions. This result was modified, however, by their finding that if Americans consumed the recommended pattern within the recommended calorie intake level of 2,000 kcal/day, there would be a 1 percent decrease in GHG emissions.

My take?  Eating too many calories likely has as much an impact on GHG as eating meat.  Reducing meat consumption would lower GHG emissions, but I would characterize the effects as "small" (3 to 4% of the GHG emissions from agriculture, or likely less than 1% of the total of all GHG emissions), particularly if people move toward pork and poultry, which have far fewer GHG emissions than ruminants like cattle.  Moreover, if we want to improve environmental impacts of livestock production, I think we're likely to get a bigger bang for our buck by improving productivity and researching new ways to reduce impacts than we will be cajoling people to eat less meat (see this paper on the reduction in environmental impact of beef production brought about over the past 40 years due to technological advancement).

What about the health impacts of meat consumption?  It is true that many observational, epidemiological studies show a correlation between red meat eating and adverse health outcomes (interestingly there is a fair amount of overlap on the authors of the dietary studies and the environmental studies on meat eating).  But, this is a pretty weak form of evidence, and much of this work reminds of the kinds of regression analyses done in the 1980s and 90s in economics before the so-called "credibility revolution." 

There have been many, many books written on the topic of whether meat eating is good or bad for you, and I won't try to adjudicate them all here.  However, I will point you to this really interesting exchange (see the comments section) on Marion Nestle's website where she mentions the new guidelines and takes a swipe at Nina Teicholz's book, Big Fat Surprise.  Nina responds, as do her critics.