The lower mortality observed in British vegetarians compared to the general population may be attributed to non-dietary lifestyle factors like low smoking prevalence, high socioeconomic status, or other dietary aspects besides meat avoidance.

“this is titled mortality in british vegetarians and it's from 2001 i've spoken about this one in the past and called it the quote uk shoppers study but what they looked at in this one were 21 000 men and women aged 16 to 18 89 years old including more than 8 000 vegetarians so it's 21 000 men and women with 8 000 vegetarians pretty good proportion and they said that british vegetarians have a low mortality compared to the general population okay but let's look at this more carefully their death rates are similar to those of comparable non-vegetarians who do healthy behaviors meaning those who have healthy behaviors in their life right so that's what they mean by comparable non-vegetarians suggesting that much of this benefit may be attributed to non-dietary lifestyle factors such as a low prevalence of smoking and a generally high socioeconomic status or to aspects of the diet other than the avoidance of meat and fish so this is really a study that illustrates the possibility of healthy user bias confounding epidemiology when we're looking at plant-based eaters or vegetarians appearing to have better mortality outcomes”