Vegetarians and pesco-vegetarians should pay close attention to the quality and composition of their diets. Not all plant-based foods are equally healthy.
Data from epidemiological studies show that people eating minimally processed plant-based foods (fresh vegetables, legumes, whole grains, fruits, nuts, monounsaturated-rich vegetable oils, tea, coffee) have lower risks of coronary heart disease and overall mortality, with regular fish intake providing additionally health benefits. In contrast, people consuming ‘unhealthy’ plant-based diets that emphasize refined grains, potatoes, high-sodium preserved vegetables, fried goods, sweets, juices, and sweetened beverages experienced a higher risk of coronary heart disease and mortality.
Commercial plant-based food products marketed as vegetarian and/or vegan can be rich in refined starch, added sugar, high-fructose corn syrup, salt, partially hydrogenated (trans) fat and saturated fatty acids from tropical oils (e.g., one tablespoon of coconut oil contains 12 grams of saturated fat). Consumption of ultra-processed foods rich in sucrose and in high-fructose corn syrup, even if labelled as ‘vegetarian’ or ‘vegan’, promotes the development of insulin resistance, cardiometabolic syndrome, fatty liver disease, cardiovascular disease, and cancer. High salt intake not only increases the risk of developing hypertension, coronary heart disease, and stroke, but it also triggers systemic inflammation.
People who consume unhealthy vegetarian diets, rich in refined, might also be at risk of protein malnutrition. Plant foods contain all nine essential amino acids but in different proportions. Legumes, for instance, are high in lysine, but low in tryptophan and methionine. In contrast, whole grains are low in lysine but high in tryptophan and methionine. Therefore, it is essential to consume every day a mixture of whole grains, beans and nuts, and/or protein-rich plant foods (e.g., tofu) to provide adequate amounts of all the essential and non-essential amino acids. Regular fish consumption can provide additional healthy proteins.
New randomized clinical trials are needed to understand whether the advantages of healthy plant-based diets represent an all-or-nothing phenomenon, and if consuming less strict plant-based diets containing small quantities of animal products (e.g., traditional Mediterranean diets) has a beneficial or detrimental effect on specific health outcomes, including the prevention of haemorrhagic stroke and bone fracture.
Further, mechanistic studies are warranted to enhance our understanding about healthy plant-based food patterns and the biological mechanisms linking dietary factors and chronic diseases.