In a study published online ahead of print in JAMA Internal Medicine,​ Michael J. Orlich, M.D. and colleagues at Loma Linda University in California, examined death rates in a group of 73,308 people in the US and Canada from the Adventist Health Study-2*, a cohort​ of 96,000 Seventh-day Adventists recruited between 2002 and 2007 and followed for an average of just under six years.

The study participants were divided into five groups: non vegetarian, semi-vegetarian, pesco-vegetarian (includes seafood, but no meat), lacto-ovo-vegetarian (includes dairy and eggs) and vegan (no animal products).

These results demonstrate an overall association of vegetarian dietary patterns with lower mortality​

There were 2,570 deaths among the study participants during an average follow-up time of almost six years and an overall mortality rate of six deaths per 1,000 person years.

The adjusted hazard ratio (HR) for all-cause mortality in all vegetarians combined vs. non vegetarians was 0.88 (12% lower), with the HR for males following a vegan diet at 0.72 (28% lower than non-vegetarians).

Vegans, lacto-ovo–vegetarians, and pesco-vegetarians all had significantly lower mortality rates compared with non vegetarians.

Looking at specific causes of death, the data also showed a significant reduction in cardiovascular disease mortality and IHD death in vegetarian vs. non vegetarian males. In women, however, there were no significant reductions in these specific categories of mortality. ​

“These results demonstrate an overall association of vegetarian dietary patterns with lower mortality compared with the non-vegetarian dietary pattern”, ​said the authors.

“They also demonstrate some associations with lower mortality of the pesco-vegetarian, vegan and lacto-ovo-vegetarian diets specifically compared with the non-vegetarian​ diet."

Why are the health outcomes of vegetarians better?​

The findings correlate with a growing body of epidemiological evidence showing that vegetarians typically have lower blood pressure, lower LDL cholesterol, a lower BMI, and lower fasting blood glucose (resulting in a lower incidence of type 2 diabetes).

But precisely why vegetarians typically have better health outcomes remains the subject of intense debate, with some researchers suggesting that vegetarians’ lower calorie intake - and lower BMI - is the critical factor from which many of the other health benefits stem; but others claiming that higher levels of fiber and health-promoting phytochemicals, coupled with lower levels of saturated fat may be responsible.

Others claim that vegetarians are healthier because they are typically better educated, more health-conscious, more likely to exercise and less likely to smoke and drink - although in the case of the AHS-2 cohort, most participants met the above profile regardless of whether they were vegetarian.

The challenge when trying to describe vegetarianism as a dietary pattern, is that there are so many different variations on the vegetarian diet​

But are all vegetarian diets the same?

Clearly not, said the authors, noting that “British vegetarians and US Adventist vegetarians eat somewhat differently”​, based on a comparison between the diets of US/Canadian vegetarians in the AHS-2 cohort and British vegetarians in the EPIC Oxford (European Prospective Investigation into Cancer and Nutrition) cohort.

For instance, the vegetarians in the AHS-2 cohort consumed significantly more fiber and vitamin C than those of the EPIC Oxford cohort - who did not enjoy an all-cause mortality advantage over their meat-eating counterparts.

Speaking to FoodNavigator-USA at the recent International Congress on Vegetarian Nutrition at Loma Linda University, Gary Fraser, PhD, one of the authors of the new study, said:

“The challenge when trying to describe vegetarianism as a dietary pattern, is that there are so many different variations on the vegetarian diet… before you even get to the difference between a vegetarian in the UK or the US versus a vegetarian in India or Africa.”​

The absence of one food -eg. meat - cannot adequately define a dietary pattern​

And then within all of these subgroups, he says, “you have the ​[ultra-healthy] vegetarians who get their protein from grains and legumes and eat a lot of vegetables, nuts and fruits; and you have the ​[far less healthy] ‘pudding and cake’ vegetarians​” (who are more likely to get their protein from a Margarita pizza and Mac & cheese instead of quinoa and lentils).

Many vegetarians - particularly the British variety, it appears - eat a bit too much pizza and cake, and not enough fruits, vegetables, beans and pulses

“However, you do generally see that vegetarians eat more fiber, less saturated fat and fewer calories.”​

"The problem is, the absence of one food -eg. meat - cannot adequately define a dietary pattern, which makes it hard to compare vegetarian research results, so it would be helpful to define and publish a recommended vegetarian diet."​

Vegetarian diets have more favorable chronic disease outcomes. This is one of the most consistent findings of nutritional epidemiology​

In a presentation at the same event urging nutrition researchers to focus on food and overall dietary patterns rather than the health benefits of isolated nutrients, David Jacobs, PhD, Mayo professor in epidemiology at the University of Minnesota, said: “In general, plant-centered and vegetarian diets have more favorable chronic disease outcomes.​

“This is one of the most consistent findings of nutritional epidemiology.”​

Meat is not the enemy ​

But meat is not the enemy, he said: “It seems that the presence of more phytochemical-rich plant foods rather than the complete absence of animal foods what makes a vegetarian diet so successful.”​

And his advice to delegates?

“We may double Michael Pollan’s seven word dictum to 14 words: Eat food. Mostly plants. Not too much. In colorful variety. Maximize nutrients per bite.”​

*The Adventist Health Study-2 cohort consists of 96,000 Seventh-day Adventists from the US and Canada. Comprehensive dietary information was gathered at study baseline (2002-2007), and then subjects were followed for mortality and cancer incidence. Sub-studies gathered blood and other bio-specimens from 2,700 subjects.

Source​: JAMA Internal Medicine​​

Published online ahead of print, June 3, 2013. 173(11):1-8. doi:10.1001/jamainternmed.2013.6473

‘Vegetarian Dietary Patterns and Mortality in Adventist Health Study 2’ ​

Authors​: Michael J. Orlich MD, Pramil N Singh DrPH, Joan Sabaté MD, DrPH, Karen Jaceldo-Siegl DrPH, Jing Fan MS, Synnove Knutsen MD, PhD, W. Lawrence Beeson DrPH, Gary E. Fraser MBchB, PhD