As a general baseline, a plant-based diet seems to be the best option for human health and longevity.

That's the conclusion reached by scientists after conducting an umbrella review of more than 20 years of data.

By carefully studying scientific literature published between 2000 and 2023, a team led by medical doctor Angelo Capodici of the University of Bologna in Italy has found humans eating vegetarian and vegan diets tend to have measurably better health outcomes in several areas.

This does not mean that you should immediately excise meat from your diet, since the dietary needs of individuals can vary significantly. What it does suggest is that making dietary changes might be a much more powerful tool than we knew for improving health outcomes, if it can be done safely.

In the last decade or so, lots of people have adopted plant-based diets for various reasons, to improve their health, cut grocery costs, or reduce their environmental impact. With this uptake in greens comes a significant increase in the data on plant-based eating, and this is what Capodici and his colleagues analyzed.

An umbrella review is like a scientific super-review – a study that collects, organizes, and analyzes the data from previous reviews and meta-analyses of prior research. So a review might cover, for example, a range of different papers that have examined vegetarianism and cancer outcomes. Another might look at cardiovascular health.

Many studies show how the food we eat affects health outcomes, with diets high in red and processed meat, refined grains, and added sugar identified as a risk factor for problems such as cardiovascular disease (CVD) and cancer.

Since diet is one of the variables that is relatively easy to change, Capodici and his colleagues wanted to take a closer look at the impact of plant-based eating on the risk of these diseases; cardiovascular diseases and cancer being the two main leading causes of death and disability worldwide.

They studied 48 reviews and meta-analyses conducted between January 2000 and June 2023, and found that vegetarian and vegan diets were associated with better health status on a number of risk factors for both cancer and CVD.

Overall, these plant-based diets were associated with better cholesterol levels and blood sugar control, a lower body mass index, and less inflammation compared to those of omnivorous eaters. People eating plant-based diets had a lower risk of both cancer and heart disease – as well as a lower mortality rate from CVD.

The team noted, though, that vegan and vegetarian pregnant women did not show a significantly lower risk of gestational diabetes and hypertension.

They were also careful not to draw conclusions about plant-based foods being the sole cause of these health improvements.

"It has also been described that vegetarians, in addition to reduced meat intake, ate less refined grains, added fats, sweets, snacks foods, and caloric beverages than did nonvegetarians and had increased consumption of a wide variety of plant foods," the team writes.

So it seems entirely reasonable that an omnivore could gain significant health benefits, not necessarily by reducing or cutting out meat, but by eating less processed food, and food high in added fat and sugar.

It's also worth noting that plant-based diets can result in vitamin and mineral deficiencies; and, of course, many different health conditions, such as allergies and gastrointestinal ailments, require a careful, tailored approach to food.

The results of the new analysis are also subject to the limitations of the original studies. Because of this, the researchers caution against the large-scale adoption of plant-based diets. Rather, they say more targeted and more specific research should be conducted, in order to narrow down why these diets are positively correlated with better health.

"Our study," the researchers say, "evaluates the different impacts of animal-free diets for cardiovascular health and cancer risk showing how a vegetarian diet can be beneficial to human health and be one of the effective preventive strategies for the two most impactful chronic diseases on human health in the 21st century."

The findings have been published in PLOS ONE.