October 2013 Issue
By Sharon Palmer, RD
Vol. 15 No. 10 P. 24
The landmark Adventist Health Study-2 has revealed new discoveries about vegetarian diets. Today’s Dietitian reports from the International Congress on Vegetarian Nutrition with this study’s results.
Perched on a foothill in San Bernardino, California—about 60 miles east of Los Angeles—the ivory buildings of Loma Linda University shine like a modern-day beacon. Loma Linda, which means “beautiful hill” in Spanish, is the home of the university and its medical center, which made international headlines in the 1980s when a surgeon at the hospital placed a baboon heart in the chest of “Baby Fae,” marking the dawn of infant heart transplants.
Today, Loma Linda is better known for headlines about the community’s longevity. The city was featured in National Geographic as one of the three places in the world with the highest longevity,1 and Dan Buettner lists it as a “blue zone,” a location where people live longer lives, according to his book The Blue Zones: Lessons for Living Longer From People Who’ve Lived the Longest.
The news on Loma Linda residents’ long life span is a product of the university’s research on Seventh-day Adventists. Considering that the university is a Seventh-day Adventist health sciences institution, a large number of people in the city practice this faith.
One of the main characteristics of Seventh-day Adventists is their healthful lifestyle practices, including discouraging cigarette smoking and drinking alcohol as well as avoiding pork, lamb, shellfish, coffee, and tea. In fact, as many as 35% of Adventists are vegetarian, and Loma Linda University is one of the few “meat-free zones” in the country. “The medical center does serve beef and chicken to patients that request it, but the cafeterias for students, employees, and patients’ families serve no meat,” says Georgia Hodgkin, EdD, RD, FADA, a professor in and the associate chair of the university’s School of Allied Health Professions.
Nutrition Scientists Take Notice
Due to these lifestyle characteristics, the Seventh-day Adventist population has been the subject of interest among epidemiologists for more than 50 years. Their observed lower risk of heart disease, cancers, high blood pressure, and arthritis drew speculation that their lifestyle—particularly related to their diet—may significantly affect health outcomes. The absence of certain lifestyle factors among Adventists, such as smoking and drinking, make other dietary factors easier to observe in research. In addition, the wide range of diets among this group, from strict vegetarian to a typical American diet, allows for researchers to investigate how various dietary patterns influence health outcomes.
In essence, Adventists are a researcher’s dream. Scientists can study the effects of different dietary patterns independent of factors such as smoking and alcohol intake, and the studies performed on this population were some of the first to demonstrate a relationship between diet and disease risk reduction.2
The first major study of Seventh-day Adventists—The Adventist Mortality Study, a prospective study of almost 23,000 California Adventists—took place in 1958. Since it occurred concurrent to the American Cancer Society study of non-Adventists, comparisons were made between the two cohorts regarding causes of death. The Adventist Health Study-1 (AHS-1), which ran from 1974 to 1988, looked at which components of the Adventist lifestyle were protective against disease. Questionnaires examining risk of developing cancer and cardiovascular disease were mailed to the more than 34,000 California Adventists who took part in the study.2
Enter Adventist Health Study-2
With the success of the AHS-1, researchers at the Loma Linda University School of Public Health were eager to forge ahead to see what more could be learned from this unique group. Thus, the landmark Adventist Health Study-2 (AHS-2) was born, which started in 2002 and included about 96,000 Adventist participants in the United States and Canada, making it one of the most comprehensive diet studies ever. It’s also one of the largest studies of blacks and offers hope that researchers can better understand why this population has a higher risk of conditions such as cancers and heart disease.3
The overarching goal of AHS-2 is to investigate the effects of soy, calcium, dairy foods, and omega-3 linolenic acid on the risks of diseases such as heart disease and cancers of the colorectum, breast, and prostate.3
The AHS-2 study subjects from more than 4,000 US and Canadian Seventh-day Adventist churches completed a 50-page questionnaire about diet, such as the frequency that specific foods were consumed, and lifestyle, such as the presence of certain health conditions. Then, every two years, the subjects complete hospitalization history forms, which gathers information about all hospitalizations.3,4
While other studies have compared Adventist cohorts with non-Adventist ones, the AHS-2 is comparing groups of people within the same cohort, which helps highlight the effects of different dietary patterns and food consumption within the population. The researchers categorized dietary patterns along a spectrum: vegans who eat no animal products; lacto-ovo vegetarians who eat no meat but do eat eggs and/or dairy foods; pesco-vegetarians who eat fish but no other meats; semivegetarians who eat meats aside from fish occasionally but less than weekly; and nonvegetarians who eat meats aside from fish at least once per week.4
Several studies based on initial data from the AHS-2 already have made headlines, with more news likely in the coming years. “We have about 10 others in progress,” says Karen Jaceldo-Siegl, DrPH, MS, an assistant professor in Loma Linda University’s School of Public Health and Medicine, who is part of the research team investigating the AHS-2. “AHS-2 is getting much attention globally in the scientific community as well as the general population. Besides AHS-2, the only other cohort with large numbers of vegetarians is the European Prospective Investigation into Cancer and Nutrition-Oxford cohort.”
Gary Fraser, PhD, MPH, led the AHS-2 research team and spoke on the study’s findings—both published and unpublished—at the International Congress on Vegetarian Nutrition, held at Loma Linda University in February. “For many years, researchers were convinced that kinds of vegetarian diets were responsible for only moderate differences in results, but there was inadequate research on vegetarian diets,” he explained. However, the AHS-2 revealed a range of benefits along the spectrum of vegetarian diets.
Food Intake Patterns
“We saw huge differences in food intake among the dietary patterns,” Fraser said at the conference, noting findings on several key nutrients in the dietary patterns, including the following:
• Soy protein and plant protein intake was much greater in vegans than in nonvegetarians.
• While the omega-3 fatty acids EPA and DHA were much lower among vegans and vegetarians, the plant omega-3 fatty acid alpha-linolenic acid was higher in this group (about 2 g/day), and higher levels of EPA and DHA were found in adipose tissue.
• Saturated fat intake was very low in vegans.
• Beta-carotene and vitamin C intake was much higher in vegans.
• Vegans and vegetarians take supplements much less than nonvegetarians.
• Vitamin B12 intake in vegans is low, but they often supplement this nutrient.
• Total iron intake is good for vegans, but it has the potential to be slightly low because typically they’re not supplementing this nutrient.
• Total calcium intake is considerably low in vegans but not in vegetarians.
One of the most intriguing discoveries of the AHS-2 so far was the linear relationship observed among the dietary patterns and many health outcomes. The following are a few highlights Fraser presented at the international congress:
• BMI: The data showed a progressive weight increase from a vegan diet toward a nonvegetarian diet. “The most striking features of the data are the great range of BMIs: The average for vegans was 23.6; lacto-ovo vegetarians, 25.7; pesco-vegetarians, 26.3; semivegetarians, 27.3; and nonvegetarians, 28.8,” he noted.
• Cardiovascular disease (CVD) risk factors: The same trend was observed for cardiovascular disease markers, such as levels of cholesterol, diabetes, high blood pressure, and metabolic syndrome, with the vegan dietary pattern demonstrating the lowest risk compared with the nonvegetarian pattern. “Regarding prevalence of hypertension, we saw large differences in the spectrum of diets between vegans through nonvegetarians. In total, the findings show a great deal of evidence for many CVD risk factors, showing that a vegetarian diet—in particular a vegan diet—is beneficial,” Fraser said.According to a study investigating data from the AHS-2 published in Diabetes Care, a vegetarian dietary pattern was associated with significantly lower averages for all metabolic risk factors, except HDL cholesterol, and a lower risk of having metabolic syndrome compared with a nonvegetarian dietary pattern.5
• Type 2 diabetes: In the case of type 2 diabetes, the prevalence in vegans and lacto-ovo vegetarians was one-half that of nonvegetarians. “We saw fewer self-reported incidences of diabetes in vegans and vegetarians than nonvegetarians, and in fasting blood glucose the same trend in data prevails,” Fraser said. These data were published in Diabetes Care, noting that the prevalence of type 2 diabetes increased from 2.9% in vegans to 7.6% in nonvegetarians; the prevalence was intermediate in lacto-ovo vegetarians (3.2%), pesco-vegetarians (4.8%), or semivegetarians (6.1%).6
• Inflammation and immune function: Fraser reported a similar trend for C-reactive protein, a measure of inflammation: “We saw a progression from vegan, lacto-ovo vegetarian, pescatarian, and nonvegetarian, with an accompanying rise in inflammation. In insulin, we saw the same pattern.”
However, he reported that there was an interesting finding with other markers of immune function, showing that insulinlike growth factor 1 and 3 weren’t different between vegans and nonvegetarians, which indicated “there’s work to be done here,” according to Fraser.
• Cancer: Benefits also were seen for cancer risk, according to Fraser, who reported that “we’re not ready to talk about individual cancers; in about a year we will publish our first paper on specific cancer risk. For overall cancer, we found that all vegetarians had an 8% reduction in risk, and vegans did best of all.
“For gastrointestinal cancers, vegetarians as a group had a 24% reduction and, in particular, lacto-ovo vegetarians did the best,” he continued. “For respiratory system cancers, the vegetarian group looked good with a 23% reduction in risk. In female cancers, vegans did the best in reduced risk.”
Fraser summarized that the vegan diet may decrease the incidence of all cancer combined, especially regarding the risk of female-specific cancers.
• Longevity: According to Fraser, “Death rates do rise across the dietary groups, from vegans to nonvegetarians. We saw that among different types of vegetarians, vegans appear to be doing well, in particular for men. When you take vegetarians together, it appears to show a significant reduction in mortality compared with nonvegetarians—about a 12% reduction. And vegans and pesco-vegetarians may fare somewhat better overall than lacto-ovo vegetarians.”
In fact, the Loma Linda University research team recently published these findings in JAMA Internal Medicine, reporting that a reduction in risk of all-cause mortality in all vegetarians combined vs. nonvegetarians was 12%, with a reduction in risk of 15% in vegans compared with nonvegetarians, 9% in lacto-ovo vegetarians, 19% in pesco-vegetarians, and 8% in semivegetarians. The researchers also reported significant associations with vegetarian diets detected for cardiovascular mortality, noncardiovascular noncancer mortality, renal mortality, and endocrine mortality, and that associations in men were larger and more often significant than were those in women.7
• Sustainability: Joan Sabaté, MD, DrPh, chair of nutrition at Loma Linda University’s School of Public Health, who also spoke at the International Congress on Vegetarian Nutrition, reported that vegetarian diets are more sustainable. According to a life-cycle assessment applied to the AHS-2 data, Sabaté reported that the greenhouse gas emissions for a vegan diet were 41.7% lower compared with a nonvegetarian diet, with a lacto-ovo vegetarian diet being 27.8% lower, a pescatarian diet 23.8% lower, and a semivegetarian diet less than 20% lower.
• Other healthful behaviors: Compared with nonvegetarians, the study found that vegans and vegetarians watched less television, slept more hours per night, consumed more fruits and vegetables, consumed less saturated fat, and typically ate foods with a low glycemic index, such as beans, legumes, and nuts.8
Looking to the Future
More information on the health benefits of vegetarian diets likely is forthcoming from continuing AHS-2 data. According to Loma Linda University, the study could continue for another 15 to 20 years, given adequate funding.
Additional questions will be addressed during the analysis of AHS-2 data, including which foods enhance quality of life, whether soyfoods can help with breast and prostate cancer prevention, whether heredity or lifestyle play a more important role in health than diet, and which foods help prevent cancer, diabetes, heart disease, Alzheimer’s disease, and arthritis.
— Sharon Palmer, RD, is a Los Angeles-based foodie, the author of The Plant-Powered Diet, the editor of the Environmental Nutrition newsletter, and a contributing editor of Today’s Dietitian.
1. Buettner D. The secrets of long life. National Geographic website. http://ngm.nationalgeographic.com/ngm/0511/feature1. May 2011. Accessed May 20, 2013.
2. History of Adventist Health Studies. Loma Linda University School of Public Health website. http://www.llu.edu/public-health/health/history.page. Accessed May 20, 2013.
3. About Adventist Health Study-2. Loma Linda University School of Public Health website. http://www.llu.edu/public-health/health/about.page?. Accessed May 20, 2013.
4. Adventist Health Study-2: early findings. Loma Linda University School of Public Health. http://www.llu.edu/public-health/health/early_findings.page. Accessed May 20, 2013.
5. Rizzo NS, Sabaté J, Jaceldo-Siegl K, Fraser GE. Vegetarian dietary patterns are associated with a lower risk of metabolic syndrome: the Adventist Health Study 2. Diabetes Care. 2011;34(5):1225-1227.
6. Tonstad S, Butler T, Yan R, Fraser GE. Type of vegetarian diet, body weight, and prevalence of type 2 diabetes. Diabetes Care. 2009;32(5):791-796.
7. Orlich MJ, Singh PN, Sabaté J, et al. Vegetarian dietary patterns and mortality in Adventist Health Study 2. JAMA Intern Med. 2013;173(13):1230-1238.
8. Lifestyle, diet and disease. Loma Linda University School of Public Health website. http://www.llu.edu/public-health/health/lifestyle_disease.page. Accessed May 20, 2013.