Plant Protein in Diet Tied to Lower All-Cause Mortality

Veronica Hackethal, MD

August 27, 2019

Eating plant protein may lower the risk for death over 18 years, a study has found.

"Our study suggests that plant protein may provide beneficial health effects and that replacement of red and processed meat protein with plant or fish protein may increase longevity," the researchers write.

Sanjeev Budhathoki, PhD, from the National Cancer Center in Tokyo, and colleagues with the Japan Public Health Center–based Prospective Study Group, published their findings online August 26 in JAMA Internal Medicine.

High-protein diets such as the paleo diet have become popular, and some short-term studies seem to support the health benefits of high-protein diets. These include more weight loss, preservation of lean muscle mass, and even improvement in cardiovascular risk factors such as cholesterol and blood pressure.

But not all research supports this view. When people eat more protein, they may decrease other nutrients in their diet, such as fiber from plants and whole grains. That, in turn, may have a negative effect on health. Also, proteins from animals and plants sources differ in nutrient composition.

To investigate the impact of high-protein diets on mortality, researchers conducted a prospective cohort study from January 1995 through December 2016.

The study included 70,696 participants with a mean age of 56 years. At baseline, participants had no history of cancer, cerebrovascular disease, or ischemic heart disease. The researchers evaluated diet using validated food frequency questionnaires that asked about consumption of 138 food and beverage items during the past year. They estimated protein intake relative to a standard portion size for a person from Japan, where the study was conducted.

The investigators adjusted results for age, sex, percent energy from different types of fats, body mass index, smoking, alcohol, physical activity, coffee and green tea consumption, and total calorie intake (excluding percentage of energy from carbohydrates).

During a mean follow-up of 18 years, 12,381 participants died.

Results suggested no clear link between eating animal protein and total or cause-specific mortality.

However, eating plant protein showed a significant association with lower risk for total death (P = .01 for trend). Individuals who ate the most plant protein had 13% lower risk for total death compared with those who ate the least plant protein (hazard ratio [HR], 0.87; 95% confidence interval [CI], 0.78 - 0.96, P = .01).

Among particular medical conditions, people who ate more plant protein had lower risk for death from cardiovascular disease (CVD; P = .002 for trend), but not from cancer (P = 0.59 for trend).

Further analyses that adjusted for diet quality, high blood pressure, abnormal blood lipids, and type 2 diabetes showed similar results.

Substituting 3% of calories from red meat with plant protein — about 260 grams or 9 ounces from a protein-rich source like soy — was linked to lower all-cause mortality (HR, 0.66; 95% CI, 0.55 - 0.80), lower cancer-related death (HR, 0.61; 95% CI, 0.45 - 0.82), and lower CVD-related death (HR, 0.58; 95% CI, 0.39 - 0.86).

That translates into an estimated absolute risk reduction at 15 years of 3.60% (95% CI, 2.10% - 4.86%) for all-cause mortality, 1.92% (95% CI, 0.87% - 2.71%) for cancer-related death, and 1.16% (95% CI, 0.39% - 1.68%) for CVD-related death.

Similarly, substituting processed meat with plant protein was linked to lower total death (HR, 0.54; 95% CI, 0.38 - 0.75) and lower cancer-related death (HR, 0.50; 95% CI, 0.30 - 0.85). Likewise, 15-year estimated absolute risk reduction would be 4.95% (95% CI, 2.62% - 6.65%) for all-cause mortality and 2.45% (95% CI, 0.72% - 3.48%) for cancer-related death.

"These types of studies generate mountains of data without providing mountains of insight," Keith-Thomas Ayoob, EdD, RD, FAND, told Medscape Medical News. Ayoob is a nutritionist and associate clinical professor emeritus in the Department of Pediatrics at Albert Einstein College of Medicine in New York City.

This was an observational study; therefore, results can only show associations but cannot prove that eating plant protein decreases mortality risk. Also, the researchers evaluated dietary intake at one point in time. Lifestyle factors, diet, and physical activity change over time, and drawing conclusions on the basis of responses 18 years later is questionable. Finally, several confounders may have complicated results. For example, people who ate high amounts of plant protein ate at least 300 fewer calories per day than people who ate a lot of animal protein. While the authors acknowledged possible residual confounding, the results leave lingering questions.

"Is what we're seeing a result of higher energy intake or protein?" Ayoob said.

The study was conducted in Japan and the results may not apply to the United States. People in the United States are becoming more familiar with plant-based protein but may prefer more processed versions compared with Japanese consumers, he added.

The bigger issue, though, may be about healthier diets: controlling portion size, eating lean protein, avoiding processed foods, and upping the intake of fruits and vegetables.

"As a clinician, having a healthier diet is a win-win for me and my patients. When people get the right amount of meat, they can then fill the rest of the plate with more plant foods" while also emphasizing exercise, Ayoob said.

"Sedentary lifestyles place more burden on dietary factors to improve health. The best health improvement most of us can make is to just move more, a lot more."

He concluded: "Studies like this can scare consumers when it should simply serve as a reminder to keep portions of all proteins real."

The authors have disclosed no relevant financial relationships. Ayoob has done work with the Beef Expert program overseen by the US Food and Drug Administration.

JAMA Intern Med. Published online August 26, 2019. Abstract

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