The best type of plant-based diet for health and environmental benefits are those higher in whole grains, fruits, vegetables, nuts, legumes, vegetable oils and tea/coffee.
Meanwhile plant-based diets high in fruit juices, sugar-sweetened beverages, refined grains, potatoes and sweets/desserts are associated with an increased risk of chronic disease and are less environmentally friendly, according to the study authors.
“The differences between plant-based diets was surprising, because they’re often portrayed as universally healthy and good for the environment, but it's more nuanced than that,” said corresponding author Aviva Musicus. She is a postdoctoral research fellow in the Harvard T.H. Chan School of Public Health's department of nutrition, in Boston.
“To be clear, we’re not asserting that less healthy plant-based diets are worse for the environment than animal-based diets. However, our findings show that plant-based diets can have different health and environmental impacts,” Musicus said in a school news release.
While previous research had documented that different types of plant-based diets have various health effects, little work had been done to determine the different environmental impacts, which can include greenhouse gas emissions, use of high-quality cropland, nitrogen from fertilizer, and irrigation water.
For the study, the researchers used data from the Nurses’ Health Study II to analyze the food intake of more than 65,000 people. The team analyzed the participants' diets both for associations with health outcomes, such as heart disease, and for environmental impacts.
The diets were scored based on whether they were higher in unhealthy refined grains, for example, or healthier whole grains.
The research team found that participants who consumed healthy plant-based diets had lower heart disease risk. Those diets were also related to lower greenhouse gas emissions and use of cropland, irrigation water and nitrogenous fertilizer compared to the unhealthy plant-based diets and to animal-based diets.
These findings also reinforced earlier studies showing that diets higher in animal-based foods, especially red and processed meat, have greater adverse environmental impacts than plant-based diets, the study authors noted.
“Because human health ultimately depends upon planetary health, future U.S. dietary guidelines should include nuanced consideration of environmental sustainability and recognize that not all plant-based diets confer the same health and environmental benefits,” according to study co-author Daniel Wang, an assistant professor in Harvard's department of nutrition.
The findings were published online Nov. 11 in The Lancet Planetary Healthjournal. The study was supported by the U.S. National Institutes of Health.
The U.S. Department of Agriculture has more on eating a vegetarian diet.
SOURCE: Harvard T.H. Chan School of Public Health, news release, Nov. 10, 2022