So what about that 2015 study? Well, that looked at data from two pre-existing studies involving more than 60,000 people. Comparing the mortality rates of those on a variety of diets, they found that there was no clear difference in mortality rates.
Other studies agree or disagree with this conclusion, and often note many confounding factors are likely influencing the data. In fact, Willett opined that the studies of vegetarians have in general not considered those aforementioned food group replacement issues sufficiently.
At present, however, there doesn’t yet appear to be a clear consensus that the vegetarian diet will help you live longer, even if research frequently suggests that they're generally healthier than meat-eaters.
Sure, the overconsumption of meat, like the overconsumption of anything, is bad for you. Diets should be nutritionally balanced and based on good science, and most rarely tick both or either of these boxes. The same, of course, applies to vegetarian diets; generalizing dietary benefits isn't all that sensible.
In any case, the UK’s National Health Service (NHS) has some excellent explainers for those wishing to try out a fully vegetarian diet. As with all diets, they offer notes of caution: For example, they explain that vegetarian sources of omega-3 fatty acids may not be as beneficial to your cardiovascular system as those obtained from oily fish.
Importantly, though, they emphasize the need to have a “healthy, balanced diet”.
Like all diets, vegetarian or no, if you’re thinking of making a change, talk to your doctor first.