Population-based studies have consistently shown that our diet has an influence on health - a diet rich in fruits and vegetables is recommended.
But some people go overboard and just eat meat. Or just eat vegetables. Evidence for health benefits of exclusive diets is scant. Vegetarians are considered healthier, they are wealthier, they are more liberal, they drink less alcohol and they smoke less - but those are a lot of variables in health that don't necessarily result from being a vegetarian.
A cross-sectional study taken from the Austrian Health Interview Survey AT-HIS 2006/07 found that vegetarians are actually less healthy than normal eaters. Subjects were matched according to their age, sex, and socioeconomic status leaving 1320 people - 330 vegetarians, 330 that ate meat but still a lot of fruits and vegetables, 300 normal eaters but that ate less meat, and 330 on a more carnivorous diet.
After controlling for variables, they found that vegetarians did have lower BMI and alcohol consumption but had poorer overall health. Vegetarians had higher incidences of cancer, allergies, and mental health disorders, a higher need for health care, and poorer quality of life.
As a result, vegetarians take more medications than non-vegetarians.
CLICK IMAGE FOR LARGER SIZE. Differences in suffering from various chronic conditions between the different dietary habit groups. doi:10.1371/journal.pone.0088278
There are limitations to this sort of study. A large number of participants and a need for controls means the questions must be kept simple. Just like vegetarians shouldn't embrace every population analysis that supports their beliefs, paleo diet people should not believe their lifestyle is necessarily healthier. People may have adopted a vegetarian lifestyle if they were already unhealthy, for example.
But as America moves more toward public health care costs, we need to counsel people about diet fads like vegetarianism just like we will smoking and junk food.
Citation: Burkert NT, Muckenhuber J, Großschädl F, Rásky É, Freidl W (2014) Nutrition and Health – The Association between Eating Behavior and Various Health Parameters: A Matched Sample Study. PLoS ONE 9(2): e88278. doi:10.1371/journal.pone.0088278