Plant-centred or low-fat diets for heart health?

Longstanding debate has focused on whether diets that are low in fat or high in plants are better for reducing the risk of cardiovascular disease.

According to the results of a new study, presented at the American Society for Nutrition's NUTRITION 2021 digital conference, while both diets were linked with lower LDL – or bad cholesterol – levels, those that were higher in plants were more closely associated with a lower long-term risk of cardiovascular disease.

"Since 1980, dietary guidelines in the United States and in Europe have recommended eating low amounts of saturated fat because of the high rates of heart disease in these regions,"​ said research team leader David Jacobs, PhD, from the University of Minnesota. "This is not necessarily wrong, but our study shows that plant-centered diets can also lower bad cholesterol and may be even better at addressing heart disease risk."​

The researchers defined ‘plant-centred’ diets as those that emphasise fruit, vegetables, legumes, whole grains, nuts and seeds, low-fat dairy, and fish. This diet also limits high-fat red and processed meats, salty snacks, sweets, and sugar-sweetened soft drinks. The low-fat diet is based on the Keys Score, a good formulation of the "low saturated fat" message, driven by saturated fat, but also including polyunsaturated fat and dietary cholesterol.

Yuni Choi, a postdoctoral fellow in Jacobs' lab, explained that while the low-fat diet does offer some advantages, focusing on a single nutrient – in this case saturated fat – is an oversimplification.

"Our findings show that it is important to view diet quality from a holistic perspective,"​ said Choi. "Targeting just single nutrients such as total or saturated fat doesn't take into account the fats that are also found in healthy plant-based foods such as avocado, extra virgin olive oil, walnuts and dark chocolate -- foods that also have cardioprotective properties and complex nutrient profiles."​

The results imply dietary strategies aimed ‘solely to lower saturated fat’ may be less effective in reducing CVD burden than recommendations for a plant-centered diet, the researchers noted.

"Based on our study, we suggest that people incorporate more nutritionally-rich plant foods into their diets,"​ said Choi. "One way to do this is to fill 70% of your grocery bag with foods that include vegetables, fruits, whole grains, nuts, legumes, coffee and tea."​

Methodology and findings

The research followed more than 4,700 people over a 30-year period. It is based on participants in the four US clinics of the Coronary Artery Risk Development in Young Adults study (CARDIA), which enrolled 5115 people between 1985-1986. During more than 30 years of follow up, there were 280 cases of cardiovascular disease, 135 cases of coronary heart disease, and 92 cases of stroke among the study participants.

To assess eating patterns, the researchers conducted three detailed diet history interviews over the follow-up period. These diet history questionnaires determined what participants ate and then asked them to list everything consumed in that category. For example, participants who reported eating meat in the past 30 days would be asked what meat items and how much they consumed. This was repeated for around 100 areas of the diet. Based on this information, the researchers calculated scores for all participants based on both the Keys Score of the A Priori Diet Quality Score (APDQS), which captures the plant-centered diet.

After accounting for various factors including socioeconomic status, educational level, energy intake, history of cardiovascular disease, smoking and body mass index, the researchers found that having a more plant-centred diet (higher APDQS Scores) and consuming less saturated fat (lower Keys Scores) were both associated with lower LDL levels. However, lower LDL levels did not necessarily correlate with lower future risk of stroke. Higher APDQS scores, but not lower Keys Scores, were strongly associated with a lower risk for coronary heart disease and stroke.

The researchers are carrying out a variety of studies looking at how the APDQS diet score relates to various health outcomes. They are also interested in studying how different diets affect gut bacteria, which is known to influence many aspects of health and disease.