Plant-based diet has the lowest greenhouse gas emissions, according to study

A recent study comparing the environmental impact and quality of several dietary patterns found that a plant-based diet had the lowest greenhouse gas emissions, albeit its quality was similar to that of other diets.

Researchers said that more studies are needed to better understand how specific food choices impact diet quality, greenhouse gas emissions, and more.

Major policy agendas have called for increasing investments in research addressing how diet patterns affect several domains of sustainability, Zach Conrad, PhD, MPH, an Assistant Professor at William and Mary, and colleagues wrote in the American Journal of Clinical Nutrition.

“The four domains of sustainability are nutrition and health, environment, economics and society,” they wrote. “Globally, food systems account for 25-35% of greenhouse gas emissions, and suboptimal diets are the leading modifiable risk factor for mortality, accounting for nine to 11 million deaths annually. Although the affordability of nutritious diets has improved, these are still financially out of reach for much of the global population, and threats to equity and inclusion are worsening.”

To meet the United Nations Sustainable Development Goals for 2030 – including better management of agricultural systems and natural resources, improved health, safe and nutritious food, safe working environments and more – food systems must be transformed for greater sustainability, the researchers added.

So, Conrad and colleagues conducted a study to compare the cost, quality and greenhouse gas emissions related to several diet patterns: plant-based, low grain, low fat, restricted carbohydrate and time-restricted diets.

To do so, they merged dietary data from more than 4,000 adults who took the 2013-2016 National Health and Nutrition Examination Survey with data on food prices and greenhouse gas emissions from multiple databases. They additionally used the Healthy Eating Index-2015 to measure diet quality.

Conrad and colleagues found that most diet patterns were linked to sustainability trade-offs, the nature of which could inform discussions on nutrition policy in the USA.

“These findings directly address key policy priorities in the National Strategy on Hunger, Nutrition, and Health to identify healthy and affordable diet patterns, which may be incorporated into public health campaigns such as the Dietary Guidelines for Americans and resources for resources for general nutrition counseling,” they wrote.

Specifically, the researchers found that the plant-based diet had:

• The lowest greenhouse gas emissions, at 3.5 kg CO2eq (95% CI, 3.3-3.8);
• A low diet cost, at US$11.51 per day (95% CI, 10.67-12.41); and
• A diet quality score of 45.8 (95% CI, 43.3-48.5) out of a maximum score of 100, which was similar to most other patterns.

“The diet quality of the plant-based diet pattern was similar to all other diet patterns except the time-restricted diet pattern,” the researchers noted.

The restricted carbohydrate diet pattern had:

• Moderate to high greenhouse gas emissions: 5.7kg CO2eq (95% CI, 5.4-5.9);
• The highest diet cost: US$18.46 (95% CI, 17.8-19.13); and
• Intermediate diet quality: 46.8 (95% CI: 45.7, 47.9).

The time-restricted diet pattern had:

• Greenhouse gas emissions similar to most other diet patterns: 4.6 kg CO2eq (95% CI, 4.2-5);
• Low to moderate diet cost: US$12.34 (95% CI, 11.38-13.4); and
• Among the lowest diet quality: 42.6 (95% CI, 40.8-44.6).

The low-fat diet pattern had:
• Intermediate greenhouse gas emissions: 4.4 kg CO2eq (95% CI, 4.1-4.6 kg);
• Intermediate diet cost: US$14.53 (95% CI, 13.73-15.38); and
• The highest diet quality: 52 (95% CI, 50.8-53.1).

For the low grain diet pattern, the researchers wrote that all sustainability impacts were intermediate.

“These findings are timely, given the rising popularity of these diet patterns and the urgent need to inform major policy discussions at the nexus of nutrition, environment and affordability,” Conrad and colleagues wrote.