ISLAMABAD, Jan 22 (Online): Intake of protein, especially from plants, in middle age is associated with higher odds of healthy aging and positive mental and physical health status in older women, a recent analysis of the Nurses’ Health Study (NHS) data suggests.
The study is said to be the first to examine the long-term impact of midlife protein consumption on later health status.
Writing in the American Journal of Clinical Nutrition, a team led by Andres V. Ardisson Korat, DSc, a nutritional epidemiologist at the USDA Human Nutrition Research Center on Aging at Tufts University in Boston, Massachusetts, found the following midlife protein-related odds ratios (ORs) for later healthy aging measured at ages 70-93.
For each 3% energy increment from various protein sources:
• 1.05 (95% CI, 1.01-1.10) for total protein
• 1.07 (1.02-1.11) for animal protein
• 1.14 (1.06-1.23) for dairy protein
• 1.38 (1.24-1.54) for plant protein
In substitution analyses, significant positive associations were observed for the isocaloric replacement of animal or dairy protein, carbohydrate, or fat with plant protein — with increased ORs for healthy aging of 1.22-1.58 for each 3% of energy replacement.
On the measure of physical function, for example, replacing calories from all macronutrient variables with equivalent calories from plant protein was associated with 20%-60% higher odds of having no physical function limitations. Plant protein was also associated with higher odds for good mental status.
“Other studies have looked at protein intake in older adults, but we felt midlife was a more relevant etiological window,” Dr Ardisson Korat said in an interview. “Our findings generally align, however, with those of protein intake in older populations, which have shown that protein can reduce the risk of frailty.”
He added that the benefits of protein, especially from plant sources, would likely apply to men as well and increasing plant protein intake is not difficult. “If you want a snack during the day, eat a handful of nuts instead of potato chips,” he advised. And eating several meals a week featuring beans, peas, lentils, tofu, whole grains, or seeds is an easy way to boost dietary plant protein, which comes with health-promoting soluble and insoluble fiber as well as antioxidant and anti-inflammatory polyphenols and other phytochemicals.
Conversely, plant but not animal protein consumption in older adulthood was linked to a lower risk of frailty in a previous NHS study.
Higher plant protein intake was associated with a better probability of achieving healthy aging defined by changes in functional impairments, self-reported health/vitality, mental health, and use of health services in the Spanish Seniors-Estudio Sobre Nutricion y Riesgo Cardiovascular.
In contrast, animal protein intake in middle adulthood has been linked to an increased risk of premature death from chronic diseases driven by cardiovascular disease mortality.
The present findings are consistent with those observed for protein intakes in older adulthood, Dr Ardisson Korat said.
“This study underscores the health advantages for midlife adults consuming adequate dietary protein — particularly plant protein — as one component of pursuing a healthy lifestyle,” said Douglas R. Dirschl, MD, chair of orthopedic surgery at Baylor College of Medicine in Houston, Texas. Most Americans consume adequate amounts of protein, but according to Dr Dirschl, who treats many older patients for osteoporotic fractures and other musculoskeletal conditions, many US diets are subpar in this nutrient.
While protein is essential for bone and muscle formation and maintenance, “a surprising number of Americans are protein deficient, even those who seem hale and are overweight,” he said.
Dietary Recommendations for Midlife Patients
Physicians should therefore advise midlife patients to meet or perhaps modestly exceed the recommended dietary allowance for protein of 0.8 g/kg per day and to make plant protein a substantial component of daily dietary protein intake, Dr Dirschl said.
Luke D. Kim, MD, MEd, a geriatrician at the Cleveland Clinic in Cleveland, Ohio, noted that patients with lower socioeconomic status or with difficulty in day-to-day functioning are likely to have suboptimal protein intake. Such patients may need encouragement to eat more protein. “But we should keep in mind that showing a higher associated odds ratio of better health with increased protein take does not mean causality,” he said.
According to Rachel L. Amdur, MD, an internist at Northwestern Medicine in Chicago, Illinois, the long-term follow-up data from the NHS are uniquely helpful. “Middle-aged persons may think they no longer need much dietary protein and need to be reminded. Sometimes eating carbohydrates is just easier,” she said in an interview. Physicians need to assess and counsel patients on nutrition at all stages of life. “As I tell my patients, it’s best to think of your future self now.”
In agreement is Louis J. Morledge, MD, an internist at Northwell Health in New York City. “I firmly counsel my patients about adequate and often increased protein intake in middle life. But this is always within a larger framework of overall nutritional health.” He added that middle-aged persons often find themselves “stuck in food ruts,” and one of his clinical focuses is to advise patients about the importance of healthier food choices so they can better adjust to mental, emotional, physical, and skeletal changes as they age.
The NHS analysis drew on prospective data from 48,762 nurses under the age of 60 years in 1984. Total protein, animal protein, dairy protein, and plant protein were derived from validated food-frequency questionnaires.
Adjusting for lifestyle, demographics, and health status, the investigators identified 3721 (7.6% of cohort) eligible participants. The mean age of participants at baseline was 48.6 years; 38.6% had body mass indexes (BMI, in kg/m2) greater than 25, 22.9% were current smokers, and 88.2% were married.
Healthy aging was defined as freedom from 11 major chronic diseases, good mental health, and no impairments in cognitive or physical function, as assessed in the 2014 or 2016 NHS participant questionnaires. Diseases/treatments included cancer, type 2 diabetes, myocardial infarction, coronary artery bypass graft or coronary angioplasty, congestive heart failure, stroke, kidney failure, chronic obstructive pulmonary disease, Parkinson’s disease, multiple sclerosis, and amyotrophic lateral sclerosis.
Mean total protein consumption as a percentage of energy was 18.3% (standard deviation, 3%), slightly higher than the average 16.0% in the US diet. Of this, 13.3% was derived from animals, 3.6% from dairy products, and 4.9% from plants.
Total protein intake was positively associated with higher education levels, being physically active, higher BMI, and a baseline history of hypertension and hypercholesterolemia. Conversely, total protein intake was inversely associated with intakes of total carbohydrates, nuts, alcohol, and sugar-sweetened beverages.
The associations between protein intake and healthy aging are complex and not fully understood, the authors stated.
Effects of Protein Intake
In studies of older adult populations, lower protein intake has been associated with lean mass loss. Animal protein supplementation studies in older adults have shown lean mass gains potentially related to amino acid composition.
In terms of mechanisms, evidence suggests that protein-related activation of the rapamycin complex 1 pathway may play a role, the authors suggested. The activity of this signaling pathway decreases with age.
Rapamycin, a compound used to prevent organ transplant rejection, has been associated with delayed aging. In the body, dietary protein and exercise activate this pathway, thereby stimulating muscle protein synthesis and possibly improving physical function.
As for the differential associations of plant and animal protein on the chronic disease domain of the healthy aging phenotype, Dr Ardisson Korat and coauthors said plant protein has been associated with favorable levels of important risk factors for cardiometabolic diseases, such as reduced LDL cholesterol, lower blood pressure, and insulin sensitivity, as well as decreased levels of proinflammatory markers.
Conversely, total and animal protein intakes have been positively associated with concentrations of insulin-like growth factor 1, which is implicated in the growth of malignant cells in breast and prostate tissue.
This study is the first step in evaluating the long-term health effect of protein intake in midlife, the relevant development window for most chronic conditions, the NHS study authors said. More research is needed, however, to corroborate the study findings in other populations and identify underlying mechanisms.
This study was supported by the USDA Agricultural Research Service and the National Institutes of Health. The authors reported no conflicts of interest. The commentators disclosed no relevant competing interests.
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