Q&A: What Tulane professor Diego Rose has learned about climate change and the American diet

Diego Rose was studying food security in New Orleans when he was invited to a three-day workshop on “ecosystem services” — the various things that nature does for humans, such as when trees absorb water and release oxygen. “I didn’t even know what ecosystem services were,” he says. Pink, professor of food and nutrition policy at Tulane University. “I had never given much thought to these things.”

The workshop changed the direction of Rose’s career. She associated with Martin Heller at the University of Michigan and began studying how Americans can make their diets more climate-friendly. She uses national data to look at what Americans eat and the environmental impacts of certain foods. most of it recent researchpublished in the American Journal of Clinical Nutrition in 2022, found that swapping one serving of beef for chicken each day would reduce a person’s dietary carbon footprint by 48%.

These questions and answers contain excerpts from two interviews, condensed and edited for clarity.

His research focuses on individual people and real diets. Where do you get data like that from?

We are working with national data from the National Health Survey and Nutrition Screening. They ask people to remember everything they ate in the last 24 hours. It’s just a snapshot: It’s a random day in the dietary life of a sample of Americans. And they have repeated it throughout the year and for several years.

So there’s pepperoni pizzas and lasagna and all sorts of other things that people eat, and those “as consumed” foods are pretty complex. If you think of a pepperoni pizza, there are tomatoes, wheat, dairy, pork, spices, and all sorts of other things. But environmental impact studies, called ‘life cycle assessments’, are all based on commodities. They are not based on food as consumed.

In our data, we have 6,000 different foods that people eat, and there are maybe 200 to 300 staples that people look to for life cycle assessment studies. So, there is this disconnect; how do you combine those two? It’s complicated.

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So how did you do it?

In the pizza example (and this was a key turning point) we found a dataset that had recipes that translated a pizza into staples.

This had been done by the Environmental Protection Agency. They were particularly interested in being able to translate what Americans ate into staples because they were regulating the use of pesticides. Therefore, they wanted to be able to estimate how much pesticide exposure people would have through diet. The only way to do that would be to be able to translate those foods as they are consumed into staple recipes.

One of the first articles coming out of this line of research was in 2018, and the team found that about 20% of Americans’ diets account for about 45% of environmental impacts [that come from food]. What are those people eating?

We started looking at those diets, breaking them down one by one, and that’s where we learned that some Americans eat a really weird combination of foods. But out of a complete set of foods, there would be one that would stand out as having a really big impact. And it was almost, not always, but many times, beef. That’s when we started looking at it systematically.

It is surprising that beef has such a large environmental impact.

The first graphic what I put together was the greenhouse gas emissions per kilogram of food. I made this chart and thought, ‘Wow, this is really dramatic.’ There’s all these numbers that are down here and then the meat goes like, up here. It’s like you have to redesign the vertical axis to fit; it’s just another magnitude of difference.

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Greenhouse gas emissions for the production of selected foods.  Courtesy of Diego Rosa
Greenhouse gas emissions for the production of selected foods. Courtesy of Diego Rosa

Why does beef have such a high carbon footprint?

All animal products have more impact than plant products because you have to grow the food and include all the impacts of those crops to feed the animals. But on top of that, with ruminant animals, there’s methane from the burp. They’re able to digest grasses, which is great if you think about it, but on the other hand, bacterial fermentation in the gut produces methane, which has 30 times the impact of carbon dioxide. So it really puts beef in a different ballpark.

You more recent research analyzes the environmental impact of changing one food for another. Tell me about your findings.

The one we started with was, What happens if you replace chicken with beef? And we’re only doing it once a day. What we find with that single substitution: reduced the carbon footprint of that person’s diet by 48%. Not your overall carbon footprint, we don’t look at your gas or heat usage or anything like that, just your dietary carbon footprint. That is quite significant.

The idea of ​​exchanging an item seems very manageable. Why did you frame the study that way?

There are some wonderful diets out there, but they are complicated. Like the Mediterranean diet: OK, what does that mean and what does it include? What is not included? So we thought instead of having this complex dietary pattern, if you could just say I’m going to have a chicken burger instead of a beef burger, it’s easier.

It’s an easy thing to recommend because you don’t have to become a vegetarian to have a big impact. If you’ve been eating a lot of beef and you can reduce the amount you’re eating, that would have a big impact.

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The study also found that swapping out a serving of beef would reduce the impact of someone’s water use by 30%. The food system has so many environmental impacts. Why did you focus on greenhouse gases and water use?

There are many different impacts of agriculture. There is only so much data that is out there. And because of that, we’ve chosen to look at what we think are the two most important things. I mean, climate-wise, we have to get greenhouse gas emissions in order. That for me is the number one priority. That said, when you have hot weather, you’re going to have more droughts. And if you have more droughts, you obviously need to use less water for food production or use it more intelligently. The deeper you dig into these things, the more nuanced they are.

It seems that the way beef is raised would make a big difference in its environmental impacts. Why don’t your studies take that into account?

Even if you were to look at beef raised with less impact, and all beef was raised that way, we would still need to cut our consumption in half to be sustainable. It’s just a high-impact food.

The US beef industry is very efficient. Efficient feedlots are terrible for animal welfare (antibiotic use and all the other problems they cause), but they raise a lot of beef without as much impact per pound of beef. The greenhouse gas emissions from those feedlots are actually lower than from the regenerative farmer in Montana who raises Bessie in the most loving way. There may be other benefits, of course, like less fertilizer, less pesticide, Bessie is happier until she dies. But unfortunately, we can’t eat as much beef as we do, even if we’re just eating lovingly raised Bessies.