By Reed Mangels, PhD, RD

Global Warming and Diet

Dietary choices have significant effects on greenhouse gas emissions. Since livestock production accounts for as much as half of lifestyle-related greenhouse gas emissions, use of meat or dairy products significantly affects an individual's carbon footprint. This effect is illustrated in two recent studies, one from the U.S. and one from the UK, which compared the estimated greenhouse gas emissions due to vegetarian and nonvegetarian diets.

Researchers from Loma Linda University determined annual greenhouse gas emissions resulting from food choices of people eating what they termed vegetarian diets (meat less than once a month), semivegetarian diets (meat less than once a week), and nonvegetarian diets1. Food choices used in this analysis were based on actual food consumption from the Adventist Health Study 2. Compared to nonvegetarian diets, semivegetarian diets reduced greenhouse gas emissions by 22% on average and vegetarian diets reduced greenhouse gas emissions by 29%, also on average. Since this study was of Seventh-day Adventists, even the nonvegetarians ate much less meat than the average American. If we were to compare a vegetarian diet (with no meat) to a typical American diet, it is likely that there would be an even greater reduction in greenhouse gas emissions.

The study from the UK compared the diets of more than 2000 vegans, close to 16,000 vegetarians, 8000 fish-eaters, and almost 30,000 meat-eaters2. Estimated greenhouse gas emissions due to dietary choices were more than twice as high for meat-eaters compared to vegans. When adjustments were made so that calories for each diet group were the same, an average 2000-calorie high-meat diet (more than 3.5 ounces of meat per day) resulted in 2.5 times more greenhouse gas emissions compared to an average 2000-calorie vegan diet. Moving from a high-meat diet (and 3.5 ounces of meat isn't really that much meat) to a vegan diet would reduce an individual's carbon footprint by 1560 kg of carbon dioxide equivalents per year. This is a greater reduction than would be seen if a family switched from driving an SUV to a Prius.

Taken together, these studies show how important dietary choices are in alleviating climate change.

1 Soret S, Mejia A, Batech M, Jaceldo-Siegl K, Harwatt H, Sabate J. 2014. Climate change mitigation and health effects of varied dietary patterns in real-life settings throughout North America. Am J Clin Nutr. 100 (suppl):490S-5S.

2 Scarborough P, Appleby PN, Mizdrak A, et al. 2014.Dietary greenhouse gas emissions of meat-eaters, fish-eaters, vegetarians and vegans in the UK. Climatic Change. 125:179-192.

Attitudes and Beliefs in Indian and Western Vegetarians: Similarities and Differences

Surveys suggest that western vegetarians tend to be concerned with animal suffering and are aware of the environmental impact of dietary choices. In India, 20-40% of the population follow vegetarian diets, often due to religious motivations. Are western and Indian vegetarians similar to each other in terms of attitudes and beliefs? To investigate this question, researchers asked Euro-American and Indian vegetarians and omnivores to complete several surveys about their food choices and their attitudes and opinions. Euro-American vegetarians were more likely to be concerned about animal welfare and the impact of their diet on the environment than nonvegetarians. There was no difference between attitudes of Indian vegetarians and nonvegetarians; both groups were less likely to have concerns about animals or the diet-environment connection than western vegetarians. A second larger study asked subjects to agree or disagree with statements such as, ''Killing and eating animals makes it easier for us to be aggressive and violent" and ''Eating meat is spiritually polluting.'' Indian and western vegetarians were more likely to agree with these statements than were nonvegetarians; the difference between vegetarians and nonvegetarians was especially strong in Indian participants. Indian vegetarians considered themselves to be more religious than did Indian nonvegetarians. Western vegetarians less strongly endorsed the values of authority (showing respect for authority and respecting the traditions of society) than did western nonvegetarians; the converse was seen in Indian vegetarians. Indian vegetarians were more likely to endorse the values of authority and tradition than nonvegetarians. Generally, vegetarians more strongly identified treating others fairly and caring for others as important values than did nonvegetarians, regardless of cultural group. These results suggest that there are both differences and similarities between western and Indian vegetarians.

Ruby MB, Heine SJ, Kamble S, Cheng TK, Waddar M. 2013. Compassion and contamination. Cultural differences in vegetarianism. Appetite. 71:340-348.

Vegetarian Wanna-bes

Some people who self-identify as "vegetarian" actually eat meat, either occasionally or frequently. Others never eat meat. Are there differences between these groups which, for convenience, we'll identify as "wanna-be vegetarians" and "true vegetarians"? More than 200 participants who identified as being "vegetarian" were recruited for a study. Vegans were not included in this study because the study researcher felt that their inclusion would complicate the interpretation of the results. Participants were asked if they readily or reluctantly consumed animal products including meat, poultry, or fish. If they refused to eat any of these products, they were classified as true vegetarians. If they readily or reluctantly ate at least one of these products, they were wanna-be vegetarians. About 28% of the self-identified vegetarians would eat some meat or fish. Study subjects were asked if their main motivation was health related or due to ethical reasons. True vegetarians were more likely to be motivated by ethics. True vegetarians were more likely to find meat disgusting, offensive, and repulsive. There was no significant difference in beliefs that humans and animals are similar between true vegetarians and wanna-be vegetarians. The study author suggests that either wanna-be vegetarians rationalize their choice to eat meat/poultry/fish by saying that animal products are delicious and satisfying or that their lack of disgust with meat, along with ingrained habits, allows them to eat meat even though their attitudes towards animals are similar to those of true vegetarians.

Rothgerber H. 2014. A comparison of attitudes toward meat and animals among strict and semi-vegetarians. Appetite. 72:98-105.

Vegetarian Pregnancy

A study from Denmark examined more than 81,000 mother-child pairs. The mothers were asked if they were vegetarian when they were pregnant and if they used multivitamins, folic acid, or iron supplements. About 1% of women self-identified as being "vegetarian," although in this study this could mean eating some fish or chicken. "Vegetarian" subjects were also classified further as those who ate fish or chicken, lacto-ovo vegetarians, and vegans. Most women, including vegetarians, took supplements during pregnancy. More than 95% of vegans took multivitamins when they were pregnant. There were no differences between the groups of "vegetarians" or between "vegetarians" and nonvegetarians in the children's development. Children of "vegetarians" actually tended to walk earlier than did children whose mothers were not vegetarians.

Larsen PS, Andersen AN, Uldall P, Bech HB, et al. 2014. Maternal vegetarianism and neurodevelopment of children enrolled in The Danish National Birth Cohort. Acta Paediatr. [Epub ahead of print]


Creatine is a nitrogen-containing compound that can be made by the human body. It is also found in meat and fish. Generally, vegetarians have a lower intake of creatine than nonvegetarians. Most of the creatine in our body is found in our muscles. A small amount is found in our brain, where it seems to play an important role in brain function. Researchers from Brazil investigated the amount of creatine in the brains of vegetarians to see if their lower dietary intake affected the concentration of creatine in their brains. The vegetarian group included lacto-ovo, ovo, and vegan vegetarians. An MRI was used to assess brain creatine concentration. There was no significant difference in brain creatine concentration between vegetarians and nonvegetarians. This suggests that vegetarians are able to make enough creatine to maintain brain creatine concentrations that are similar to those of nonvegetarians.

Yazigi Solis M, de Salles Painelli V, Giannini Artioli G, et al. 2014. Brain creatine depletion in vegetarians? A cross-sectional 1H-magnetic resonance spectroscopy (1H-MRS) study. Br J Nutr. 111, 1272-1274.