SCIENTIFIC UPDATE

By Reed Mangels, PhD, RD

Vegetarian Diets and Blood Pressure

Close to one-third of adults in the U.S. have high blood pressure. Although high blood pressure usually doesn't make people feel sick, it increases their risk for heart disease and stroke, two of the most common causes of death. Researchers at Loma Linda University recently reported the results of a study examining blood pressure in white Seventh-day Adventists. In this small study, 504 people were categorized as “vegan” (10 percent of the group; ate meat, fish, dairy less than once a month), ‘lacto-ovo vegetarianÂ’ (36 percent of subjects; ate meat and fish less than once a month), “partial vegetarian” (14 percent; ate meat and fish less than once a week), and “non-vegetarian” (40 percent). Subjects had their blood pressure measured and were asked about use of medications to treat high blood pressure. The average blood pressure of the entire group was relatively low; approximately a quarter of all study subjects were taking medicine to treat high blood pressure. Looking only at subjects who were not taking blood pressure medicine, subjects classified as “vegans” or “lacto-ovo vegetarians” had the lowest blood pressure. This was partly, but not entirely, due to differences in Body Mass Index (BMI) since overweight people tend to have higher blood pressure than people who weigh less. Subjects classified as vegans or lacto-ovo vegetarians had a much lower risk of having hypertension (excessively high blood pressure) compared to non-vegetarians. Protective factors in a vegetarian diet may include higher intakes of potassium (a mineral found in fruits, vegetables, whole grains, and other plant-based foods) and fiber.

Pettersen BJ, Anousheh R, Fan J, et al. 2012. Vegetarian diets and blood pressure among white subjects: results from the Adventist Health Study-2 (AHS-2). Public Health Nutr 10:1-8.

Red Meat and Mortality

A recently published study used data from two very large studies, the Health Professionals Follow-Up Study (more than 37,000 men studied) and the Nurses' Health Study (close to 84,000 women) to assess the association between red meat intake and mortality. Subjects did not have heart disease or cancer at the start of the study. They were observed for up to 28 years, and records were kept on food consumption, development of diseases, and deaths. The more red meat (including both processed and unprocessed meat) subjects ate, the greater their risk was of dying due to heart disease or cancer. A one-serving-per-day increase in total red meat consumption was associated with a 16 percent higher risk of dying of heart disease and a 10 percent higher risk of dying of cancer. If only processed meat (hot dogs, bacon, bologna, etc.) was examined, a one-serving-per-day increase was associated with a 21 percent higher risk of dying of heart disease and a 16 percent higher risk of dying of cancer. The researchers estimated that, if red meat consumption had been limited to less than half a serving per day, 8.6 percent (men) and 12.2 percent (women) of deaths from heart disease during the follow-up period would not have occurred.

In an editorial accompanying this report, Dean Ornish, MD, recommends eating plant-based foods and concludes, “In addition to their health benefits, the food choices we make each day affect other important areas as well. What is personally sustainable is globally sustainable. What is good for you is good for our planet.”

Pan A, Sun Q, Bernstein AM, et al. 2012. Red meat consumption and mortality: results from 2 prospective cohort studies. Arch Intern Med 172:555-63.

Ornish D. 2012. Holy Cow! What's good for you is good for our planet: comment on “Red Meat Consumption and Mortality.” Arch Intern Med 172(7):563-64.

Vegetarians, On Average, Have Earlier Age at Menopause

Menopause, the cessation of menstrual periods, occurs, on average, between the ages of 48 and 52 in American and European women. Older age at menopause is associated with a higher risk of breast cancer. A large study, from the United Kingdom, of more than 50,000 women recently reported on factors that can affect the age at which women reach natural menopause. The average age at menopause was 50.7 years. Women who weighed more, had a higher Body Mass Index (BMI) at age 40, who gained more weight between ages 20 and 40, who had more children, or who regularly drank alcohol tended to have a later age at menopause. Women who reported that they followed a vegetarian diet or who smoked were younger at menopause. Vegetarian women's average age at menopause was 50.1 years, compared to 50.7 years for non-vegetarians. The earlier age at menopause was seen in both women who became vegetarian before they were 20 years old and in women who became vegetarian between the ages of 20 and 40 years. These results were similar to other studies that have shown earlier natural menopause in vegetarians as well as a later menopause in women who ate larger amounts of meat. The earlier average age of menopause seen in vegetarians may provide some health benefits, including a lower risk of breast cancer.

Morris DH, Jones ME, Schoemaker MJ, et al. 2012. Body mass index, exercise, and other lifestyle factors in relation to age at natural menopause: analyses from the breakthrough generations study. Am J Epidemiol 175:998-1005.

Motivations of Current and Former Animal Product Limiters Are Different

Some people make a gradual change to a vegetarian or vegan diet, while some change overnight. Some people stay vegetarian for many years, and others do not. The Vegetarian Resource Group has examined the motivations of people who remain vegetarian or vegan. (See www.vrg.org/research/retention_survey_2009.php for more information.) Researchers from Western Washington University recently compared motivations of current and former animal product limiters. Current animal product limiters were categorized as vegans (118), lacto-ovo vegetarians (48), fish-eaters (22), and others (8). Most had been limiting animal products for more than six years. Former animal product limiters were categorized as now eating meat once or twice weekly (more than half), eating meat regularly (15), or eating meat if there were no other choices (5).

Current limiters tended to be younger than former limiters and were more motivated by ethical food choices and by health. Their eating pattern tended to be more of a part of their self-identity compared to former limiters. Vegans were more likely to be motivated by ethical and environmental factors than were lacto-ovo vegetarians or fish-eaters. Health motivations were similar among all three groups. Former animal product limiters cited factors such as difficulty with preparing foods, boredom, and cravings for meat as the main reasons for returning to meat-eating. They were more likely to have made the initial change to a vegetarian or near-vegetarian diet abruptly and not to have had support from a vegetarian or vegan group.

These results suggest that motivations and factors such as self-identity and involvement with a vegetarian or vegan group can make it more likely that people will stay vegetarian or vegan.

Haverstock K, Forgays DK. 2012. To eat or not to eat. A comparison of current and former animal product limiters. Appetite 58:1030-36.

Vegetarian Diet May Improve State of Mind

Some researchers believe that the type of dietary fat that people eat can affect their moods. Non-vegetarian diets are often high in arachidonic acid. High intakes of this fatty acid have been shown to lead to changes in the brain that can have a negative effect on mood. Fatty acids found in fish (DHA and EPA) are supposed to have a positive effect on mood. Despite this, one study has found that vegetarians report having a better frame of mind than non-vegetarians, even though the non-vegetarians had higher intakes of DHA and EPA.

To examine this further, researchers divided 39 non-vegetarians into three groups. One group ate their usual diet (meat or poultry at least once daily), one group ate fish three to four times a week but avoided meat, and one group ate a vegetarian diet (no meat, fish, or poultry) for two weeks. Subjects completed questionnaires about their mental state at the beginning of the study and after two weeks of their assigned diet. Over the two-week study period, subjects eating a vegetarian diet had lower levels of stress and tension than the other two groups. This is a small, preliminary study, but it suggests that dietary changes can have positive effects on mood.

Beezhold BL, Johnston CS. 2012. Restriction of meat, fish, and poultry in omnivores improves mood: a pilot randomized controlled trial. Nutr J 11:9.