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Issues Of The Environment: American Dietary Habits Impact On Greenhouse Gas Emissions

Apr 4, 2018

Dr. Martin Heller, research specialist at the University of Michigan Center for Sustainable Systems
Credit University of Michigan Center for Sustainable Systems / umich.edu

The UM Center for Sustainable Systems recently published research findings that 46% of total food-based, greenhouse gas emissions in America come  from the diets of just one-fifth of the population.  In this week’s "Issues of the Environment," 89.1 WEMU’s David Fair talks with lead researcher Martin Heller about the research process and his findings. 


Overview:

  • The UM Center for Sustainable Systems recently published research finding that 46% of the total emissions from food came from the diets of just one-fifth of the population.
  • This research was exhaustive and detailed (see “Methods for Measuring GHG Emissions”).  To estimate the impact of U.S. dietary choices on greenhouse gas emissions, the researchers built a database that assessed the environmental impacts involved in producing more than 300 types of foods.  Then they linked the database to the findings of a nationally representative, one-day dietary recall survey involving more than 16,000 American adults.
  • They found that Americans in the highest-impact quintile consumed more than twice as many calories on a given day—2,984 versus 1,323—than those in the bottom 20 percent.  But even when the findings were adjusted for caloric intake, the highest-impact quintile was still responsible for five times more emissions than the lowest-impact group.
  • Meat accounted for 70 percent of the food-associated greenhouse gas emissions in the highest-impact group but only 27 percent in the lowest-impact group.
  • If has long been known that diets rich in animal proteins, particularly beef and dairy, leave a heftier carbon footprint.  Martin Heller, Research Specialist for the UM Center for Sustainable Systems, suggests that policies and recommendations aimed at reducing GHG emissions attributed to food might focus on marketing foods that are good for the planet and eating fewer excess calories.
  • While is appears that vegetarian or vegan diets would be better for the environment, this may not always be the case.  In fact, Carnegie Mellon published a study finding that “healthier” diets, high in certain vegetables and seafood, actually consumed more energy than diets rich in animal proteins, including pork and chicken.

Abstract from Martin Heller's Research

Human food systems are a key contributor to climate change and other environmental concerns. While the environmental impacts of diets have been evaluated at the aggregate level, few studies, and none for the US, have focused on individual self-selected diets. 

Such work is essential for estimating a distribution of impacts, which, in turn, is key to recommending policies for driving consumer demand towards lower environmental impacts.  

To estimate the impact of US dietary choices on greenhouse gas emissions (GHGE) and energy demand, we built a food impacts database from an exhaustive review of food life cycle assessment (LCA) studies and linked it to over 6000 as-consumed foods and dishes from 1 day dietary recall data on adults (N = 16 800) in the nationally representative 2005–2010 National Health and Nutrition Examination Survey

Food production impacts of US self-selected diets averaged 4.7 kg CO2 eq. person−1 day−1 (95% CI: 4.6–4.8) and 25.2 MJ non-renewable energy demand person−1 day−1 (95% CI: 24.6–25.8).  

As has been observed previously, meats and dairy contribute the most to GHGE and energy demand of US diets; however, beverages also emerge in this study as a notable contributor.  Although linking impacts to diets required the use of many substitutions for foods with no available LCA studies, such proxy substitutions accounted for only 3% of diet-level GHGE. 

Variability across LCA studies introduced a ±19% range on the mean diet GHGE, but much of this variability is expected to be due to differences in food production locations and practices that can not currently be traced to individual dietary choices. 

When ranked by GHGE, diets from the top quintile accounted for 7.9 times the GHGE as those from the bottom quintile of diets.  Our analyses highlight the importance of utilizing individual dietary behaviors rather than just population means when considering diet shift scenarios. 

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— David Fair is the WEMU News Director and host of Morning Edition on WEMU.  You can contact David at 734.487.3363, on twitter @DavidFairWEMU, or email him at dfair@emich.edu