I’ve been a vegetarian my entire adult life, so I’m always pleased when a new study comes out, as one did earlier this week, suggesting that vegetarians tend to live longer. After all, who doesn’t want to have their dietary (or other lifestyle choices) validated by science?
But, despite the fact that I would personally welcome a study that proved vegetarianism superior to carnivorism, that proof just doesn’t exist. Not even in the headline-catching findings of this latest study, published Monday in the journal JAMA Internal Medicine.
What the new study found is more evidence of an association between following a vegetarian diet and a longer life. That’s not the same as finding evidence of a cause-and-effect.
Still, the study has a lot of strengths. It was large, for example, and its participants were more diverse than many past studies on vegetarianism in terms of race, socioeconomic status and geography. In addition, its pool of participants had an overall low use of tobacco and alcohol, which made it less likely that those lifestyle factors confounded the results.
So, it’s a study worth taking a look at.
Five dietary groups
For the study, researchers at Loma Linda University followed 73,308 members (mean age: 58) of the Seventh-day Adventist Church for almost six years. The church’s teachings encourage a vegetarian diet and discourage the use of tobacco, caffeine and alcohol. Many, but not all, of its members follow those tenets. In this study, for example, 52 percent of the participants were vegetarians of some kind.
At the beginning of the study, the participants filled out a detailed questionnaire about their eating habits. Based on their answers, they were then placed in one of five dietary categories: nonvegetarian (a diet that includes poultry and red meat), semi-vegetarian (poultry and red meat, but no more than once a week), pesco-vegetarian (no poultry and red meat, but includes seafood), lacto-ovo-vegetarian (no poultry, red meat or seafood, but includes dairy products and eggs) and vegan (no animal products of any kind).
By the end of the study, 2,570 of the participants had died. The Loma Linda researchers compared those death records to the dietary choices on the questionnaires and found that a vegetarian diet (broadly defined by the researchers as everybody except the nonvegetarians) was associated with a 12 percent lower risk of death.
The benefit was greatest among pesco-vegetarians (a 19 percent lower risk of death) and vegans (a 15 percent lower risk). Among lacto-ovo-vegetarians, the reduced risk of death was 9 percent, which was just slightly better than that of the semi-vegetarians (8 percent).
The Loma Linda researchers came to those percentages after adjusting for a variety of confounding factors, including body mass index (BMI), smoking, exercise habits, calorie intake and educational level.
Protecting the heart
A closer look at the study’s data provided some additional interesting findings. Most striking was the discovery that vegetarianism was strongly associated with a healthier heart. Those in the vegetarian groups were 19 percent less likely than their meat-eating peers to die from heart disease.
The study found no added protection against cancer, however.
In addition, the study found that men were much more likely than women to benefit from forgoing meat. Being a vegetarian was associated with an 18 percent drop in the overall death rate (and a whopping 29 percent drop in heart-disease-related deaths) among the study's male participants, but with only a 7 percent drop among its female ones.
“It is possible,” write the Loma Linda researchers, “that within dietary groups the diets of men and women differ in important ways.”
Dietary goals
As already noted, this study’s results don’t prove that eliminating meat from one’s diet is a recipe for a longer, healthier life. (Among the study’s many limitations is the fact that the participants filled out only one questionnaire about their dietary choices. Those choices may have changed significantly over the course of the six years.)
Still, as Dr. Robert Baron, a general internist from the University of California, San Francisco, points out in an editorial that accompanies the study, we have enough good evidence to know what our overall dietary goals should be:
Although nutrition authorities may disagree about the optimal balance of macronutrients in an ideal diet, and the amount of meat and other specific foods that should be ingested, virtually all agree that diets should limit added sugars and sugary drinks, refined grains, and large amounts of saturated and trans fats. Similarly, virtually all diet recommendations include eating substantial amounts of fruits and vegetables. Most authorities will also agree that diets should include whole grains, legumes, and nuts.
Achieving these goals trumps the more narrow goals of whether to include moderate amounts of dairy, eggs, fish, or even meat.
Unfortunately, both the study and the editorial are behind a paywall at the JAMA Internal Medicine website.