Nutrition in the elderly: a recommendation for more (evenly distributed) protein?

See corresponding article on page 113.

In the past century, ∼30 y have been added to human life expectancy. The result is a globally aging population that, although rich in opportunities, also presents important challenges. Governments, agencies, institutions, and families will be faced with a scenario in which nutrient requirements for older persons are not a passing thought but a stark reality.

A primary concern of many aging persons and their caregivers is mobility. Declines in physical mobility are critical because they are strongly aligned with the risk of disability, cognitive impairment, institutionalization, falls, and mortality (1). As a well-developed paradigm, a nutritional focus in aging has deservedly been on bone health to prevent osteopenia and osteoporosis (2). In contrast to a fracture, however, there is a lack of a well-defined clinical endpoint for the decline and loss of function of skeletal muscle or what we now call sarcopenia. And yet, like bone, skeletal muscle mass and function are immanently modifiable. Analogous to bone, skeletal muscle is mechanically sensitive and is stimulated to turn over, favoring net accretion, with loading. Dietary protein has also been shown to be a modifiable dietary factor that, when consumed at higher-than-recommended (i.e., the Recommended Dietary Allowance of 0.8 g · kg⁻¹ · d⁻¹) quantities, can abate declines in muscle mass (3). Critically, requirements for dietary protein in older persons appear to be greater than those in younger persons (4). It has also been shown that protein consumption at meals throughout the day can influence muscle mass (5). Such a conclusion is in accordance with the known dose-response relation of protein and muscle protein synthesis (6) and results from shorter-term trials (7). In fact, interventions in which lower protein–containing meals have been “topped up” with supplemental protein have shown increased muscle mass in middle-aged persons (8).

In this issue of the Journal, Farsijani et al. (9) add an important extension to their earlier findings from the NuAge cohort (5). Previously, these authors showed that older (∼74 y old) men and women with evenly distributed protein intakes and men with higher protein intakes had higher whole-body and appendicular lean mass (5). Farsijani et al. (9) report that a more evenly distributed protein intake across meals, independently of total quantity of protein, was associated with a higher muscle strength score in both men and women. Interestingly, a more evenly distributed protein intake was also associated with a greater mobility score, but only in men. What more evenly distributed protein intakes were not associated with was the decline in strength and mobility over 2 y of follow-up, a finding congruent with a similar decline in muscle mass from the authors’ earlier work (5). Thus, an emerging picture for protein and muscle bears a striking resemblance to what has long been advocated for calcium, vitamin D, and bone to attenuate the risk of osteopenia and osteoporosis: to accrue adequate bone mass and density before age-related loss. Thus, older persons should aim to build up as much of a functional muscle mass (homeostatic reserve) as they can to provide a buffer against age-related sarcopenia and, ultimately, age-related physical frailty. In fact, such a concept underpins much of the narrative messaging around dietary protein intakes, per-meal protein distribution, and age-related sarcopenia (10). Importantly, impairment in physical function represents the core feature shared by both sarcopenia and physical frailty. But paramount is the recognition that sarcopenia, as a biological precursor of physical frailty, is immanently amenable to treatment through both physical activity and, as Farsijani et al. have persuasively shown, higher and more evenly distributed dietary protein intakes (9). These observational findings shed vital insight into the potential impact that per-meal protein recommendations may have on skeletal muscle mass and function in older persons. Farsijani et al. provide us with a demonstration that there are bona fide functional consequences associated with dietary protein, its per-meal consumption, and muscle mass (5) and function in older persons (9). This growing body of evidence begs the question: Are we ready to acknowledge that older persons have a greater requirement for protein, as many have shown (4), and perhaps on a per-meal basis?

The author reported the receipt of competitive funding, travel support, and honoraria from the US National Dairy Council.