Carnegie Mellon University
November 02, 2015

Weighing Environmental Impacts of Obesity in US Population

Weighing Environmental Impacts of Obesity in US Population

Michelle TomMichelle Tom

In the United States, over two-thirds of the adult population is overweight or obese. As individuals, we all know that this excess weight is bad for our health and our futures. But is it also bad for the planet as a whole? In what ways does our weight impact the mark our society leaves on an already delicate environment?

Over the past three years, CEE PhD student Michelle Tom, with guidance from advisors Chris Hendrickson and Paul Fischbeck, has been studying the food supply chain and the transportation sector to answer these questions.

From growing, processing and transporting food, to food sales and service, and, finally, to household storage and use, feeding a nation unavoidably takes a toll on our resources in the form of energy use, water withdrawals and greenhouse gas (GHG) emissions.

So could eating healthier not only benefit us, but also the environment? The answer, Tom found, is complicated.

On the one hand, her results show that eating fewer calories, as recommended by the 2010 USDA dietary guidelines, could reduce energy use, water withdrawals and GHG emissions from within the food supply chain by around 9%.

Yet, following guidelines on calories and on the USDA recommended mix of fruit, vegetables, dairy, seafood, and other food groups leads to a different result. In this case, by eating healthier as a nation, we would likely increase our environmental impact across all three categories measured in her research.

How so? “There’s a complex relationship between diet and the environment,” explained Tom. Largely though, you can blame the fruits and vegetables.

While the USDA recommends eating more fruits and vegetables, produce typically requires not only the greatest energy use per calorie to get to our tables, but also relatively high GHG emissions and water withdrawals to grow, irrigate and harvest. So, while cantaloupe, for example, might be better for our waistlines, potato chips are better for the environment.

“What is good for us health-wise isn’t always what’s best for the environment,” she said. “That’s important for public health officials to know and for them to be cognizant of these tradeoffs as they develop or continue to develop these dietary guidelines in the future.”

In addition to studying the impact of our diet on the environment, Tom has also studied the effects of increased weight on fuel use, greenhouse gas emissions, and fuel costs in transportation in the US.
In this area, the results are a bit clearer. “In the transportation sector, what’s good for public health is also good for the environment,” she said.

According to their research, from 1970 to 2010, over 205 billion additional liters of fuel was consumed in light-duty vehicles, transit systems and passenger aircraft to support extra weight of the American population, resulting in 503 million metric tonnes of CO2-eq and $103 billion of extra fuel cost.

Thus, even while fuel efficiency technology and policies have improved, additional passenger weight could be offsetting these gains toward a more sustainable future. In fact, their research predicts that if our population’s weight continues increasing at the same pace over the next 50 years, total excess fuel use could result in an extra 1.1 billion metric tonnes of CO2-eq and $200 billion of additional fuel costs.

What these findings mean for future guidelines and policy is yet to be seen, but, for dietary guidelines in particular, Tom sees a need for “cooperative efforts between policy makers, health officials and consumers.” For now, she believes drawing attention to these issues is a good starting point.

“Being aware of the relationship between excess population weight and environmental sustainability is the first step.”

Impact per Calorie bar chart: Indices of average energy use, blue water footprint, and GHG emissions per Calorie of food for each food group. An index score of 100 represents the highest resource use and emissions per Calorie. Scores were developed based on the weighted averages of energy use, blue water footprint, and GHG emissions per Calorie estimates for comparable food types within each food group. Whiskers represent the range of scores based on the minimum intensity values for all food types and the maximum intensity values for all food types.