Log on to Twitter and you might read: "A vegetarian diet is associated with poorer health, a higher need for health care, and poorer quality of life." Here we have junk science going viral! And its fanning the flames between meat-eating and vegetarian advocates. But it shouldn't.
You can't really blame the person pushing out this tweet too much, however, because her source is a study published in a PLOS One research paper. It highlights some of the pitfalls associated with paying too much attention to isolated studies that rely on questionable methodology and overblown claims.
This study is another example of how junk science adversely impacts public policy debates, which is why I recently developed A Consumer's Guide to Chemical Risk: Deciphering the “Science” Behind Chemical Scares.” As this study on vegetarian diets shows, it's not just chemical policy that's negatively impacted by bad science. Personal choice, should rule the day when it comes to dietary choices, but because government is so involved -- setting guidelines and telling us what we should and shouldn't eat -- food politics are unavoidable. Accordingly, meat-eaters might use this dumb study to push their agenda, but the facts do not really support them.
This study placed all vegetarians into one category, but there is no such thing as a single vegetarian diet. For example, some vegetarian diets might include mostly processed food and french fries, while others consist of nuts, beans grains, and fresh vegetables. It makes no sense to lump these diets into one category. Yet there are no more details in this study about what the vegetarian participants' diets included and when the participants began them. Nor does the study include any empirical medical data; just reports from individuals about their perceived health profile.
Apparently, assessing the value of any particular diet was not really the point of this study, despite its conclusions. Rather it addresses the subjects lifestyles' and perceptions about them, and it found that vegetarians (at least the Austrians in this survey) worry more about their health and report having more health problems than do meat eaters. It does not demonstrate that a vegetarian diet can't be as healthy as or healthier than a diet that includes meat.
Yet the authors somehow conclude:
Moreover, our results showed that a vegetarian diet is associated with poorer health (higher incidences of cancer, allergies, and mental health disorders), a higher need for health care, and poorer quality of life. Therefore, public health programs are needed in order to reduce the health risk due to nutritional factors.
This conclusion offers lots of opportunity for anti-vegetarian soundbites, but the study really doesn't show what this conclusion says. First the "association" does not prove cause-and-effect; and second it's not a vegetarian diet that causes these problems. It's the alleged lifestyles of the vegetarians, such as not getting vaccinated as often and not pursuing preventative health check-ups.
There are many other reasons to doubt such a strong sounding conclusion. First, the sample is hardly random: 76 percent were women, about 60 percent were under 40 years old (30 percent were under 30 years old).
There are many potential confounding factors, but the researchers tried to control for some: body mass index (BMI), physical activity, smoking behavior, and alcohol consumption. Controlling for confounding factors is a tricky and imperfect process. And it is curious as to why they would control for BMI since lower BMI it is an indicator of good health, and, as the study reported, the vegetarians had lower BMI.
The study authors admit that there are many problems with their own study. For example:
Our results have shown that vegetarians report chronic conditions and poorer subjective health more frequently. This might indicate that the vegetarians in our study consume this form of diet as a consequence of their disorders, since a vegetarian diet is often recommended as a method to manage weight and health.
Note the phrase "subjective health." Also, this points out that it's not necessarily a vegetarian diet that caused the illnesses. Rather, illnesses may have motivated people to make vegetarian choices.
Here is another one:
Unfortunately, food intake was not measured in more detail, e.g. caloric intake was not covered. Hence, further studies will be necessary to analyze health and its relationship with different forms of dietary habits in more detail.
In other words: The data do not provide a complete enough snapshot of dietary choices.
Potential limitations [emphasis original] of our results are due to the fact that the survey was based on cross-sectional data. Therefore, no statements can be made whether the poorer health in vegetarians in our study is caused by their dietary habit or if they consume this form of diet due to their poorer health status. We cannot state whether a causal relationship exists, but describe ascertained associations.
Moreover, as noted, this study relies on self-reporting by the individual participants to assess health differences rather than actual medical exams. Such subjective data collection methods are highly suspect because of recall and other biases from both participants and researchers. For example, the study attempts to measure "quality of life," which is a very subjective concept.
This study simply is not useful for drawing any meaningful conclusions. Yet it will likely continue to be part of a larger debate about food choices, which the study suggests should be the case. In the study, the authors call for "public health programs" to address "the health risk due to nutritional factors" that they suggest are related to be vegetarian. That's not only dumb, it just wrong.