In a study of more than 100,000 postmenopausal women, those who ate larger amounts of plant-based protein showed lower risk of premature death, cardiovascular disease and dementia-related death compared to women who ate more animal-based proteins. The findings suggest that health outcomes can be influenced by the form that dietary protein takes, not just the amount of protein consumed.

"Our findings support the need to consider dietary protein sources in future dietary guidelines," said Wei Bao, lead author of the study published Wednesday in Journal of the American Heart Association and an assistant professor of epidemiology at the University of Iowa. "Current dietary guidelines mainly focus on the total amount of protein, and our findings show that there may be different health influences associated with different types of protein foods."

Red meat consumption is a well-known risk factor for cardiovascular disease and associated mortality, but research is still determining the role of other protein sources like poultry and fish in cardiovascular disease. A 2020 study from the Journal of the American Medical Association found that red meat, processed meat and poultry are all significantly associated with cardiovascular disease, but fish is not.

Further, the role that different types of proteins, such as plant proteins, play in heart health is less documented. Research into the role that dietary protein types play in other illnesses affecting older women, like dementia, is similarly scarce, but this field is beginning to expand as more and more people are affected.

“Dementia is really on people’s radar much more now, and for two reasons,” said Penny Kris-Etherton, a professor of nutritional science at Pennsylvania State University and immediate past chair of the AHA Council on Lifestyle and Cardiometabolic Health. “Baby boomers are aging, so we’re seeing an increase in prevalence that way. People are also living longer, and since dementia is a late-stage disease, we’re seeing it a lot more than when people were dying before 70.”

To start to answer the outstanding questions, researchers used survey data from 102,521 women aged 50 to 79 enrolled in the Women’s Health Initiative, a long-term national health study funded by the National Heart, Lung, and Blood Institute (NHLBI) within the National Institutes of Health. The participants were all recruited between 1983 and 1988 and followed until 2017.

The participants completed questionnaires about their diet, including how often they ate eggs, dairy, poultry, red meat, shellfish and plant proteins such as tofu, nuts, beans and peas.

When comparing women who ate the most plant protein with those who consumed the least, they found that the former had a 9% lower risk of premature death from any cause, and a 12% lower risk of death from cardiovascular disease and a 21% lower risk of dementia-related death.

More surprisingly, higher consumption of red meat was associated with a 20% higher risk of dying from dementia. While some studies have linked dementia to red meat, these connections are not well-understood and are not fully agreed-upon among researchers. Some research, including a 2016 ecological study from the Journal of the American College of Nutrition, has identified a strong link between red meat consumption and dementia.

However, other papers, including a 2019 study from the Journal of Alzheimer’s Disease and Parkinsonism, suggest a less-direct link, proposing that there may be an element of bias in research connecting red meat to dementia.

The role that red meat plays in dementia outcomes has proven difficult to confirm compared with those for cardiovascular disease because much less is known about the biological mechanisms surrounding dementia.

“We have really good, detectable biomarkers for cardiovascular disease — mainly high blood pressure and high cholesterol,” said Kris-Etherton. This makes a really nice, tight picture when we study cardiovascular disease. For dementia, there are no biomarkers. We don’t really understand dementia and cognitive decline the same way we do heart disease.”

Eggs were somewhat of a special case in this study. While higher consumption of eggs was associated with a 14% lower risk of dying from dementia, it was associated with a 10% increase in risk of dying from cancer and a 24% risk of dying from cardiovascular disease.

“It is unclear in our study why eggs were associated with a higher risk of cardiovascular and cancer death," said Bao. "It might be related to the way people cook and eat eggs. In the United States, people usually eat eggs in the form of fried eggs and often with other foods such as bacon.”

The researchers also found that replacing meat, eggs and dairy with nuts or legumes decreased the risk of death from all causes by between 17% and 47% depending on the particular substitution. This suggests that there may be additional benefits to eating nuts.

“These proteins aren’t consumed in isolation. When you decrease the beef, you increase other things like nuts,” said Kris-Etherton. “This study found a lot of benefits of nuts — so you have to ask: Is it really the red meat, or are we seeing benefits of the nuts?”

While there remains much to learn about the role of plant-based proteins in dementia, and in health outcomes for people of all ages, this study adds to the growing body of evidence supporting a plant-rich diet in promoting heart and general health.

The paper “Association of Major Dietary Protein Sources With All-Cause and Cause-Specific Mortality: Prospective Cohort Study” was published Feb. 23 in Journal of the American Heart Association. The authors of the study were Yangbo Sun, Buyun Liu, Linda G. Snetselaar, Robert B. Wallace and Wei Bao, University of Iowa; Aladdin H. Shadyab, University of California, San Diego; Candyce H. Kroenke, Kaiser Permanente Division of Research; Bernhard Haring, University of Würzburg; Barbara V. Howard, MedStar Health Research Institute and Georgetown/Howard Universities Center for Clinical and Translational Science; James M. Shikany, University of Alabama at Birmingham; and Carolina Valdiviezo, Medstar Washington Hospital Center and Georgetown University School of Medicine. The lead author was Wei Bao.