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Green Eats

Carbon footprint study reveals 1 'recommended' diet is bad for Earth

"Human food systems are a key contributor to climate change."

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Research suggests switching to a plant-based diet is one way a person can help reduce the impacts of climate change.

However, the U.S. dietary guidelines — nutritional advice published every five years by the Department of Agriculture and the Department of Health and Human Services — recommend "core elements" of a healthy diet that include dairy and various proteins.

Therein lies the BBQ rub. According to a study published Monday in Nutrition Journal, these guidelines may be helpful for the body — but they're not great for the planet.

According to the study, the carbon footprint of the recommended U.S. dietary guidelines is higher than that of any of the six other countries analyzed, including both lower-income countries like India and higher-income countries like Germany.

Diego Rose, a co-author on the study and Director of Nutrition at Tulane University's School of Public Health & Tropical Medicine, tells Inverse the study suggests the U.S. government needs to rethink its approach to diet.

"Human food systems are a key contributor to climate change, so it's irresponsible for governments to produce dietary guidance without considering their impact on the environment," Rose says.

A plant-based curry. Plant-based diets contribute significantly less to greenhouse gases. Getty

What kind of diet is best for the environment?

By and large, plant-based diets are much better for the environment than animal-based ones.

For example, CarbonBrief analyzed data comparing plant-based "Impossible" meat and "Beyond Burgers" to beef burgers. The carbon footprint for the plant-based burgers was 20 times smaller than the beef burgers.

Recently, researchers have suggested adapting the Mediterranean diet — a favorite for its health benefits — to be more "green" by cutting out red meat and increasing plant intake.

This study dives into this question, finding what's best for the environment doesn't always align with what governments say is best as a diet.

Which food has the largest environmental impact?

According to the study, the livestock industry accounts for around 14.5 percent of total global manmade greenhouse gases.

Red meat, like beef, has a particularly devastating impact, emitting up to 60 kilograms of carbon dioxide per kilogram of meat consumed.

How does your diet affect climate change?

Food systems account for up to a whopping 29 percent of global, human-produced greenhouse gas emissions, according to Rose and his colleagues.

(For more information on how diets impact climate change, you can read the EAT-Lancet's report, which focuses on how best to feed a global population through sustainable diets.)

A chart showing consumption patterns by country.

This study produced four findings pertaining to the U.S. carbon footprint:

  • U.S dietary recommendations were linked to the highest carbon footprint at 3.83kg CO2-eq/d.
  • The U.S guidelines were 4 times the carbon footprint of India (0.86 kg CO2-eq/d).
  • U.S/ recommendations were higher than other developed countries — 19 percent and 47 percent higher than those of the Netherlands and Germany, respectively.
  • The carbon footprint of the standard U.S. guidelines was more than twice as much as the U.S. vegetarian guidelines.

The high carbon footprint in the U.S. can largely be attributed to the higher amounts of protein — especially animal-based protein — and dairy in the recommended guidelines. Dairy and animal meat both contribute significantly to greenhouse gases.

For example, the U.S. dietary guidelines recommend more than twice as much protein as India and six times as much dairy as Oman.

How they did it — While prior research has focused on the environmental impact of a single country's dietary guidelines, researchers in this study wanted to compare the impacts across countries.

They chose seven countries with a variety of dietary habits: Germany, India, the Netherlands, Oman, Thailand, Uruguay, and the United States.

They acquired the countries' specific dietary guidelines, using supplementary data from the UN Food and Agriculture Organization to calculate the consumption of specific food groups within each country.

The researchers then calculated the greenhouse gas emissions from each dietary guideline, assuming a 2000-calorie diet.

Red meat on a tray. The study highlights how greater animal protein in US dietary guidelines contributes to greenhouse gas emissions.Getty

Digging into the details — The research isn't without its limitations, however.

For example, greenhouse gas is the only factor considered in this study, but other sustainability issues — such as land use — don't receive consideration.

Through their study, the researchers also addressed another dilemma that had been puzzling sustainability experts and nutritionists.: In prior research, nearly every country reduced its carbon footprint when diets shifted toward the recommended national guidelines — except for the U.S.

By breaking down the unsustainable elements of the standard (non-vegetarian) U.S. dietary guidelines, the research team in this study effectively resolved that puzzle.

Why it matters — The numbers don't lie.

The study states that food systems contribute up to 29 percent of manmade greenhouse gases worldwide, and agricultural livestock accounts for 14.5 percent of global greenhouse gases.

That number is expected to rise as the global population grows to an estimated 9.8 billion people by 2050, especially as urbanizing countries consume more meat and less plant-based products. The study authors write:

"The dual burden of recent global dietary change on health and the environment presents a global challenge."

Therefore, the study suggests it will be paramount for "governments to promote diets that are both nutritious and sustainable and incorporate these recommendations" into specific policies. Some countries, like the Netherlands, are already doing this.

This is especially pertinent in the U.S., considering its outsized impact on greenhouse gas emissions. The U.S. ranks second only to China in terms of its carbon dioxide emissions.

A figure from the study showing the impact of greenhouse gas emissions by each country's dietary guidelines.

What's next — For his part, Rose has one specific request for countries, specifically, the U.S: change your guidelines to incorporate sustainability.

"I'd like to see environmental impacts included in the development of dietary guidelines," Rose tells Inverse. "Given the pressing nature of the problem, it's time to consider this issue in [the] development of the next set of dietary guidelines."

Unfortunately, a lot of politicking goes into these guidelines, and incorporating sustainability was a challenge during the previous administration, which routinely downplayed the effects of the climate crisis.

"Our current guidelines [2020-2025] do not include mention sustainability, and it was intentionally excluded from the previous version by the government, despite significant discussion of it by the expert committee," says Rose.

Rose mentions that the U.S dietary guidelines get revised every five years, through a joint process between the US Departments of Agriculture and Health and Human Services, which seek out expert opinions. As it turns out, the set of guidelines are being developed very soon, according to Rose.

The study mentions three specific ways that countries can change their guidelines to reduce their carbon footprint

  • Reduce the daily recommended amount of dairy and protein
  • Incorporate a plant subgroup (e.g., legumes) within the protein category
  • Encourage consumption of plant-based substitutes (such as soy milk)

"There is plenty of opportunities to include sustainability in this process," says Rose.

Abstract:
Background: Do the environmental impacts inherent in national food-based dietary guidelines (FBDG) vary around the world, and, if so, how? Most previous studies that consider this question focus on a single country or compare countries’ guidelines without controlling for differences in country-level consumption patterns. To address this gap, we model the carbon footprint of the dietary guidelines from seven different countries, examine the key contributors to this, and control for consumption differences between countries.
Methods: In this purposive sample, we obtained FBDG from national sources for Germany, India, the Netherlands, Oman, Thailand, Uruguay, and the United States. These were used to structure recommended diets using 6 food groups: protein foods, dairy, grains, fruits, vegetables, and oils/fats. To determine specific quantities of individual foods within these groups, we used data on food supplies available for human consumption for each country from the UN Food and Agriculture Organization’s food balance sheets. The greenhouse gas emissions (GHGE) used to produce the foods in these consumption patterns were linked from our own database, constructed from an exhaustive review of the life cycle assessment literature. All guidelines were scaled to a 2000-kcal diet.
Results: Daily recommended amounts of dairy foods ranged from a low of 118 ml/d for Oman to a high of 710 ml/d for the US. The GHGE associated with these two recommendations were 0.17 and 1.10 kg CO2-eq/d, respectively. The GHGE associated with the protein food recommendations ranged from 0.03 kg CO2-eq/d in India to 1.84 kg CO2-eq/d in the US, for recommended amounts of 75 g/d and 156 g/d, respectively. Overall, US recommendations had the highest carbon footprint at 3.83kg CO2-eq/d, 4.5 times that of the recommended diet for India, which had the smallest footprint. After controlling for country-level consumption patterns by applying the US consumption pattern to all countries, US recommendations were still the highest, 19% and 47% higher than those of the Netherlands and Germany, respectively.
Conclusions: Despite our common human biology, FBDG vary tremendously from one country to the next, as do the associated carbon footprints of these guidelines. Understanding the carbon footprints of different recommendations can assist in future decision-making to incorporate environmental sustainability in dietary guidance.
Keywords: Food-based dietary guidelines, Global warming, Greenhouse gas emissions, Carbon footprint, dataFIELD, FAO food balance sheet