A recent study from researchers at Harvard T.H. Chan School of Public Health indicates that consuming more plant-based proteins relative to animal-based proteins may lower the risk of cardiovascular disease (CVD) and coronary heart disease (CHD). The findings suggest that this reduction in risk is primarily due to substituting red and processed meats with plant proteins. Furthermore, the researchers discovered that a combination of increasing plant protein consumption alongside a higher overall protein intake yields the best outcomes for heart health.
Although global dietary guidelines advocate for a greater intake of plant protein, the optimal ratio of plant to animal protein had not been clearly defined. This study is the first to explore this ratio and its effect on health, particularly concerning heart health.
“Currently, the typical American diet has a plant-to-animal protein ratio of 1:3. Our research indicates that a ratio of at least 1:2 is much more effective in lowering the risk of CVD. For preventing CHD, a ratio of 1:1.3 or higher should come from plant sources,” explained lead author Andrea Glenn, a visiting scientist in the Department of Nutrition. Glenn, who is now an assistant professor at New York University, contributed to this study while serving as a postdoctoral fellow at Harvard Chan School.
The results will be published on December 2 in the American Journal of Clinical Nutrition.
The study utilized three decades of data concerning diet, lifestyle, and heart health from nearly 203,000 participants in the Nurses’ Health Studies I and II, as well as the Health Professionals’ Follow-up Study. Participants provided dietary information every four years. The researchers calculated each person’s total protein intake in grams per day, as well as their specific consumption of animal versus plant proteins. The study recorded a total of 16,118 cases of CVD, including over 10,000 cases of CHD and more than 6,000 strokes during the follow-up period.
After controlling for factors such as participants’ health backgrounds and demographic variables, the study found that a greater ratio of plant-to-animal protein was linked to reduced risks of CVD and CHD. Participants with the lowest plant-to-animal protein ratio (~1:4.2) had a 19% higher risk of CVD compared to those with the highest ratio (~1:1.3), who exhibited a 27% reduced risk of CHD. The risk reductions were even more pronounced among those with higher total protein consumption. Participants getting the majority of their energy from protein (21%) while maintaining a higher plant-to-animal ratio experienced a 28% lower risk of CVD and a 36% lower risk of CHD than those with the least protein intake (16%). There were no significant connections found between the protein ratio and stroke risk; however, substituting red and processed meats with various plant-based sources, such as nuts, appeared to lower the stroke risk.
The researchers also investigated whether there is a threshold beyond which increasing plant protein consumption offers diminishing returns or potentially negative effects. They found that while CVD risk reductions begin to level off around a 1:2 ratio, the risk of CHD continues to decrease as the ratio of plant to animal protein increases.
The researchers believe that the observed risk reductions likely stem from replacing red and processed meats with various plant protein sources, especially nuts and legumes. Such dietary adjustments have been shown to enhance cardiometabolic risk markers, including cholesterol levels and blood pressure, as well as inflammatory indicators. This is partly attributed to plant proteins being rich in fiber, antioxidants, vitamins, minerals, and healthy fats.
“We need to start shifting towards diets rich in plant-based proteins,” stated senior author Frank Hu, Fredrick J. Stare Professor of Nutrition and Epidemiology at Harvard Chan School. “This can be achieved by reducing meat consumption, particularly red and processed meats, and increasing the intake of legumes and nuts. These dietary changes benefit not only our health but also that of the planet.”
The researchers highlighted that the ratios they propose are approximations, and further investigations are necessary to establish the ideal balance of plant and animal proteins. Additional research is also needed to understand how protein intake might affect stroke risk.
The Nurses’ Health Studies and Health Professionals Follow-up Studies were funded by grants from the National Institutes of Health, numbers UM1 CA186107, R01 CA49449, R01 HL034594, U01 HL145386, R01 HL088521, U01 CA176726, R01 CA49449, U01 CA167552, R01 HL60712, and R01 HL35464.
