Scientific Update
A Review of Recent Scientific Papers Related to Vegetarianism
by Reed Mangels, PhD, RD, FADA
The Effects of Our Food Choices on the Earth
By Priscila C. Reis, VRG Intern
Food systems were responsible for 34% of all global greenhouse gas emissions in 2015, as well as for 70% of world freshwater use and for 78% of water pollution. Are some diets a greater burden on the ecosystem than others? To answer that question, researchers from the University of Oxford analyzed diets of subjects from a large study of what 55,504 United Kingdom adults were eating between 1993 and 1999. Study subjects self-identified as vegans, vegetarians, fish eaters, or meat eaters.
The information on what people ate was linked to another database that included life-cycle assessments from 38,000 farms located in 119 countries. Life-cycle assessments analyze the environmental impacts of food products and could include their growth, production, shipping, and other factors. This analysis provided information such as estimates of greenhouse gas emissions, water use, land use, water pollution, eutrophication risk, and biodiversity loss.
All of the environmental indicators showed that the more animal-based food that is consumed, the greater the impact. In comparison to diets high in meat (three or more ounces of meat daily), vegan diets resulted in about 75% lower greenhouse gas emissions. Land use and eutrophication risk were around 70% lower with vegan diets. Vegan diets also had a much lower impact on biodiversity and on water use.
The relation between environmental impacts and animal-origin food consumption is clear and should prompt its reduction. Plant-based diets are much more sustainable and must be supported and encouraged by government policies, such as environmental labeling on foods and taxation of high-carbon foods. Other measures, including financial benefits for sustainable growers and reducing the prices of plant foods, could help to increase consumption of plant foods.
Scarborough P, Clark M, Cobiac L, et al. Vegans, vegetarians, fish-eaters and meat-eaters in the UK show discrepant environmental impacts. Nat Food. 2023; 4:565-574.
Vegan Diet Improves Cardiovascular Health: Results of a Twins Study
Identical twins offer an opportunity to study people who are genetically very similar and raised in similar environments. A recent study featured 22 pairs of twins who were randomly assigned to follow either a healthy vegan diet or a healthy omnivorous diet for eight weeks. Both diets emphasized vegetables, fruits, and whole grains and limited sugar and refined grains. The nonvegan diet included, on average, 6-8 ounces of meat, fish, or poultry; 1 egg; and 1.5 servings of dairy each day. The vegan diet included, on average, 5 servings of legumes, nuts, seeds, or vegan meat.
Participants were told to eat until they were full; weight loss was neither encouraged nor discouraged. For the first four weeks of the study, a meal delivery service was provided to study participants free of charges. For the remaining four weeks, participants prepared their own foods.
At the end of the eight-week study period, the group eating a vegan diet had a significant improvement in LDL-cholesterol, fasting insulin, and weight compared with the omnivore group. These results are especially striking since both groups ate healthier diets than they were eating prior to the study. The fact that the study compared one identical twin to another makes it more likely that changes in health outcomes are mainly due to differences in diets.
Landry MJ, Ward CP, Cunanan KM, et al. Cardiometabolic effects of omnivorous vs. vegan diets in identical twins: A randomized clinical trial. JAMA Netw Open. 2023;6(11):e2344457.
Vegan Diets Associated with Less Air Pollution
Food production, especially animal agriculture, is a major source of emissions of ammonia and methane, both of which contribute to air pollution and its associated health risks, including heart and lung disease. European researchers investigated the theoretical impacts on air quality of changing from a meat-heavy diet to more plant-based diets. They examined "flexitarian" diets, which had low levels of animal products, vegetarian, and vegan diets. A global dietary change to a flexitarian diet would reduce agricultural emissions by 44-48% and to a vegetarian diet would reduce emissions by 69-70%. A global change to vegan diets was the most effective, reducing emissions by 84-86%.
The reduction in emissions would decrease the number of early deaths due to air pollution. A global change to a vegan diet would result in 236,000 fewer deaths per year. In regions with high population density and intensive agriculture, such as Europe and North America, premature deaths due to air pollution could be reduced by approximately 20% per year.
These results suggest that moving towards more plant-based, ideally vegan, diets could be an effective way to reduce air pollution and the health impacts associated with air pollution.
Springmann M, Van Dingenen R, Vandyck T, et al. The global and regional air quality impacts of dietary change. Nat Commun. 2023;14:6227.
Healthier Plant-Based Diet Associated with a Lower Risk of Cognitive Impairment in Older Adults in China
A study of more than 6,600 adults older than 65 years, living in China, followed participants for a median of 10 years. The study determined the amount of "healthy plant foods" and "less healthy plant foods" that study subjects ate at the beginning of the study and after three years of the study, and the change in "plant-based dietary quality" over those three years was calculated. Changes in cognitive impairment were assessed in the last seven years of the study. Mild cognitive impairment is believed to be a precursor for dementia. Those subjects who had a large increase in plant-based dietary quality, meaning they ate more "healthy plant foods," had a significantly lower risk of developing cognitive impairment. Those who had a large increase in their consumption of "unhealthy plant foods" had a significantly higher risk of developing cognitive impairment. Greater increases in meat and fish intake were also associated with a higher risk of cognitive impairment. Although subjects were not necessarily vegetarian, this study points to the potential importance of choosing healthy plant foods such as whole grains, beans, fruits, vegetables, and nuts.
Ding K, Zeng J, Zhang X, et al. Changes in plant-based dietary quality and subsequent risk of cognitive impairment among older Chinese adults: A national community-based cohort study. Am J Clin Nutr. 2023;118:201-208.
Do International Dietary Guidelines Consider Climate Change?
Many countries, including the United States, have food-based dietary guidelines. These guidelines provide advice about what constitutes a healthy diet using commonly eaten foods. Guidelines are often the foundation of nutrition policies to be used by schools, the food industry, and others.
Globally, food systems are responsible for a third of human-induced greenhouse gas emissions. A recent study examined the extent to which dietary changes to benefit the environment are included in dietary guidelines from 92 countries.
About 40% of countries acknowledged the link between environmental sustainability and food choices. The most common advice was to choose local and seasonal foods to reduce emissions due to transportation. While this offers some economic and health benefits, transportation accounts for less than 5% of global food-related emissions. Only about a quarter explicitly called for reducing meat consumption; just one country recommended reducing dairy consumption, while eight encouraged increased dairy consumption.
Overall, most countries did not fare well on a scoring system this study developed to assess the degree to which dietary guidelines included advice about reducing food-related greenhouse gas emissions. The median score was 31 out of 100—failure in any grade book.
Aguirre-Sanchez L, Teschner R, Lalehandani NK, et al. Climate change mitigation potential in dietary guidelines: A global review. Sustain Prod Consum. 2023;40:558-570.
