A diet rich in protein — especially plant protein — may keep women healthier as they age, a new study suggests.

In an analysis of data from more than 48,000 women, researchers found that each 3% increase in the amount of plant protein consumed was associated with a 38% higher likelihood of staying healthy as the women got older, meaning fewer or no chronic diseases, better physical mobility and little cognitive decline, according to the report published in the American Journal of Clinical Nutrition on Wednesday. 

“In particular, plant protein, seemed to be favorably associated with good mental health status and a lack of impairments in memory,” said the study’s lead author, Andres Ardisson Korat, a scientist at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University.

“The advantage of consuming more plant protein — compared to other nutrients in the diet — is that plant protein is associated with a lower risk of cardiovascular disease and other chronic conditions,” he said, adding that plant protein also promotes good physical function by enhancing muscle synthesis.

Moreover, plant protein “comes from food sources that typically contain high-quality carbohydrates, containing more fiber, vitamins and minerals, and antioxidants,” Ardisson Korat said. 

To see how protein consumption affects healthy aging, the researchers looked at surveys from more than 48,000 participants in the Nurses’ Health Study, a long term investigation into the risk factors for major diseases in women. The data was collected every four years from 1984 to 2016 and tracked how frequently people ate certain foods. At the start of the study, the women were between the ages of 38 and 59 and were in good physical and mental health.

For the new analysis, the researchers calculated protein intake by multiplying the number of times each food item was consumed by its protein content and then totaled the amount of protein across all food items.

For women to be categorized as healthy by the time they were between 70 to 93, they had to be free from the major chronic health conditions associated with aging in the U.S.: cancer (except for nonmelanoma skin cancer); Type 2 diabetes; cardiovascular diseases; stroke; kidney failure; Parkinson’s disease; multiple sclerosis; and amyotrophic lateral sclerosis, or ALS.

Adult women, 31 to 59, need the equivalent of 5 ounces to 6 ounces daily, according to the recommended dietary allowance (RDA). A 3% increase in protein in a 2,000-calorie diet — typical for middle-aged women — is  60 calories or half an ounce of protein, Ardisson Korat said.

This amount of protein could be found in one cup of cooked beans or cooked lentils.

However, with every calorie of protein added to the diet, something else needs to be switched out, such as refined carbs or unhealthy fat, Ardisson Korat said.

Early in the study, the sources of plant proteins included bread, vegetables, pasta, potatoes, nuts, beans and peanut butter.

Plant foods that are relatively high in protein include:

• Lentils.
• Green peas.
• Spinach.
• Broccoli.

The women who ate more plant proteins were 46% more likely to be healthy into their later years, the analysis showed. Women who consumed more animal protein, such as beef, chicken, milk, fish and cheese, however, were 6% less likely to stay healthy as they aged.

However, because the women in the Nurses’ Health Study were mostly white, it’s unclear how the findings would apply to other groups. 

The new report amplifies results of earlier studies that have shown that people who consume plant proteins, especially those who are vegetarians, tend to be healthier with lower cholesterol levels, a better ability to burn calories and lower levels of inflammation and dementia.

Nutrition studies are rarely done as controlled clinical trials and the new research was based on food questionnaires, so it doesn’t prove that increasing plant proteins helps with healthy aging.

However, the many years of follow-up provide confidence in the findings, said Marie-Pierre St-Onge, an associate nutrition professor at the Columbia University Vagelos College of Physicians and Surgeons in New York City.

She said the focus on prolonged health as opposed to disease or death was refreshing.

“While we all want an increased life expectancy, we really want those extra years to be in a healthy state,” St-Onge said.

Cardiologist Deepak Bhatt, director of the Mount Sinai Fuster Heart Hospital in New York City, said the finding about plant proteins is backed by other evidence that they are good for reducing heart attacks and cancer risk.

“I would encourage both women and men to adopt a plant based diet,” he said.

Cardiologist Dr. Kathryn Lindley, director of the Women’s Heart Center at the Vanderbilt University Medical Center in Nashville, noted that there could be other reasons that people who were eating a lot of plant protein might have been healthier in their old age.

For example, the women eating more protein might have healthier diets overall or they might be living a healthier lifestyle overall, she said. Or, they may been able to afford more quality food choices and had better access to health care and exercise facilities.

Yet, even with limitations, the study is “a good starting point,” Lindley said.