Specialists have repeatedly noted the health benefits of diets with a consistent plant intake. It is said that such diets can prevent or alleviate the symptoms of various diseases, including obesity, diabetes, hypertension, and heart disease.

In the United States, approximately 610,000 people die of heart disease every year, according to the Centers for Disease Control and Prevention (CDC). The CDC highlight poor nutrition, among others, as a driving factor for developing a heart condition.

One previous study targeted the possible benefits of a plant-based diet containing predominantly whole grains, legumes, vegetables, fruits, and flaxseed for preventing and overcoming coronary artery disease.

Another analysis showed that plant-based diets are good for people diagnosed with ischemic heart disease, while a further report recommended the consumption of fruits and vegetables to prevent the onset of coronary heart disease.

Now, a new and more comprehensive study brings to light the health benefits and risks of different types of plant-based diet. The research was conducted by specialists from the Harvard T.H. Chan School of Public Health and Brigham and Women's Hospital, both in Boston, MA.

An article describing the process and presenting the findings, the lead author of which is Dr. Ambika Satija, is published in the Journal of the American College of Cardiology.

Unhealthful plant foods can cause harm

For the purpose of this investigation, the researchers recruited adult participants from three different health studies. The participants comprised 166,030 women from the Nurses' Health Study and the Nurses' Health Study II, and 43,259 men from the Health Professionals Follow-Up Study.

The participants were followed-up for a period of more than 20 years, using biennial questionnaires that assessed their lifestyle, medical history, and health behaviors.

The study excluded as unsuitable all those who had declared a diagnosis of coronary heart disease or cancer, experienced a stroke, or undergone coronary artery surgery.

Of the baseline healthy population, 8,631 participants developed coronary heart disease during the follow-up period.

One preliminary consideration for the researchers was that previous studies tended to deem all plant-based diets "vegetarian," without making a distinction between different kinds of plant-derived foods and their respective benefits or disadvantages.

Therefore, the researchers decided to take a more focused approach, coming up with three kinds of plant-based diet. These were:

• diets that maximized plant food intake but did not entirely exclude animal-derived nutriments
• solely plant-based diets that maximized intake of healthful plant foods (such as fruits, vegetables, and whole grains)
• plant-based diets consisting mostly of unhealthful plant-derived food (including sweetened beverages, potatoes, sweets, and refined grains)

It was found that participants who had adhered to a healthful plant-based diet - excluding animal-derived products and including fruits, vegetables, and whole grains - had a substantially reduced risk of developing heart disease. But the researchers also noted that consumption of unwholesome plant-derived foods, such as refined grains, had a negative impact on the heart.

"When we examined the associations of the three food categories with heart disease risk, we found that healthy plant foods were associated with lower risk, whereas less healthy plant foods and animal foods were associated with higher risk [of heart disease]," says Dr. Satija.

'Crucial' food quality considerations

The editorial that accompanies Dr. Satija and her colleagues' article - written by Dr. Kim Allan Williams, from Rush University Medical Center in Chicago, IL - emphasizes the importance of this new study.

Dr. Williams commends the evidence gathered by following the participants for such a long period of time, adding that it is increasingly important that specialists recommend the consumption of the right kind of plant-based products.

"It's apparent that there is a wide variation in the nutritional quality of plant foods, making it crucial to take into consideration the quality of foods in a plant-based diet," adds Dr. Satija.

Although the study is limited by the fact that the participants self-reported their dietary adherences, these reports were confirmed through biomarkers and detailed multiple-week records of their food intake.