Dietary Changes in Subset of Population Can Contribute to Climate Goals

By Lisa Rapaport

April 09, 2020

(Reuters Health) - Healthy eating guidelines may only prompt a small subset of the population to change their diets in favor of foods produced with fewer greenhouse gas emissions, but researchers say these shifts might still be good for the planet.

The agricultural sector produces about one quarter of the world's greenhouse gas emissions (GHGE), and meat production, especially beef, is an important contributor to global GHGE, researchers note in The Lancet Planetary Health. The current study aimed to address fundamental gaps in the diet-climate literature: how to identify consumers who are receptive to making dietary changes, and the effect of their potential changes on GHGE, diet healthfulness, and diet costs.

"Previous research indicated that the carbon footprint of diets could be reduced by consuming less meat and more plant-based protein foods, like beans, nuts, and seeds," said Diego Rose, a professor and director of nutrition at the School of Public Health & Tropical Medicine at Tulane University in New Orleans and the study's senior author.

"Such substitutions typically improve the healthiness of the diet and reduce its cost," Rose said by email. "But previous studies mostly evaluated aggregate (country-wide) diets or those generated by computer optimization."

For the current study, dietary data on U.S. individuals from a nationally-representative survey were linked to food-related GHGE. Researchers identified individuals receptive to changing their diets (potential changers) as those who reported trying U.S. dietary guidance and were likely to agree that humans contribute to climate change.

The study sample included 7,188 individuals, of whom 16% were potential changers. These were disproportionately women, highly educated, or had higher income compared with those deemed not likely to change their eating habits.

Researchers assessed GHGE, diet healthfulness measured by the Healthy Eating Index (HEI), and diet costs before and after hypothetical changes replacing either beef or all meats with poultry or plant-protein foods.

Replacing 100% of beef intake with poultry reduced mean dietary GHGE by 1.38 kg CO2-equivalents per person per day, a 35.7% decrease. This replacement also increased mean HEI by 1.7% and reduced mean diet costs by 1.7%.

The largest changes occurred when replacing all beef, pork, or poultry intake with plant-protein foods: GHGE decreased by 49.6%, mean HEI increased by 8.7%, and dietary costs decreased by 10.5%.

Hypothetical replacements in the potential changers alone resulted in whole-population reductions in 1-day dietary GHGE of 1.2% to 6.7%, researchers calculated.

That's because the production of red meat (beef or lamb) is responsible for 10 times the emissions of greenhouse gases as chicken and 20 times that of nuts, seeds, or legumes, Rose said. Cows produce a lot of methane in their digestive systems, which is a potent greenhouse gas.

"All animal products have a higher impact than plants because you have to raise the animals, as well as the crops to feed them," Rose said. "So, when people eat less meat, less meat will get produced, with a lower impact on the environment."

Plant-based diets are healthier because they have more fiber, less saturated fats, and, compared to processed meats, less sodium, Rose added. Such diets promote reduced blood levels of LDL-cholesterol, lower blood pressure, and ultimately reduced rates of cardiovascular disease, Rose said.

One limitation of the study is that potential "changers" already consumed less beef and pork at baseline than other individuals, and researchers didn't know exactly how much beef they consumed. This makes it hard to accurately estimate how much they could reduce their beef consumption or what impact this might have on the climate.

Another limitation is that researchers didn't investigate other dietary changes that might accompany a reduction in beef consumption or determine any secondary effects on production, market supply, beef prices, or eating habits of non-changers.

Food production also has other environmental impacts, particularly on water and land use, that were not examined in the study.

Still, the results should give added encouragement to people who are willing and ready to cut back on red meat and consume more plant-based meals, said Dr. John Potter of the Centre for Public Health Research at Massey University in Wellington, New Zealand.

"The way to go is plant-based," Potter, who wasn't involved in the study, said by email.

"Start with Meatless Mondays, move gradually but determinedly towards a major reduction, take time to adapt, and learn from plant-based cuisines all round the world," Potter advised. "Everyone does not need to be vegan or vegetarian but, as Western societies, we are eating about 10 times more meat than we have ever seen across human history, 10 times more meat than is good for the planet, and 10 times more meat than is good for our health."

SOURCE: The Lancet Planetary Health, online March 20, 2020.