Physical weakness is a sizable component of age-related frailty. The loss of muscle mass and strength that accompanies aging, known as
sarcopenia, has many potential contributing causes, with varying degrees of accompanying evidence. One of these is dietary, a lower protein intake in older individuals, and dysfunction in processing of amino acids such as leucine. That this correlates with frailty, as illustrated here, doesn't necessarily mean that it is an important cause, however. The alternative is that the factors that lead to reduced dietary intake in later life are distinct issues that arise from similar root causes to those of sarcopenia: consider something as simple as increased difficulty when swallowing, for example. When it comes to mechanisms, there is better evidence for chronic inflammation produced by cellular senescence or declining stem cell function to be primary causes in sarcopenia, and these are not particularly related to dietary protein intake.
Frailty can be defined as a state of augmented sensitivity and vulnerability to external stressors in old age. The Fried frailty phenotype classifies frailty as the presence of three or more of the following five components: weakness, slowness, low physical activity, exhaustion, and weight loss, and prefrailty as the presence of one or two of the Fried phenotype criteria. In a recent systematic review carried out in 61,500 individuals aged 65 and older, the overall prevalence of frailty was estimated to be 10.7%, and 41.6% were prefrail with one or two components of Fried frailty phenotype.
There is growing support for the concept that greater protein intake may preserve physical function in older adults. The anabolic response to amino acid intake may be blunted in older people, particularly if they have low intakes of protein. In addition, animal protein intake may be associated with muscle strength in older adults, which may be associated with a lower risk of frailty; whereas, plant-based protein sources may have limited potential to stimulate the skeletal muscle anabolic response. The exact reasons are not understood but it might be that plant proteins are considered to have a lower content of essential amino acids compared to animal protein sources. Nevertheless, knowledge regarding the association between adequate protein intakes, according to recommendations, and sources of protein intake with frailty are limited.
We hypothesized that the prevalence of frailty and prefrailty was lower among older women consuming ≥ 1.1 protein/kg body weight (BW) compared to those with lower intakes. Participants were 440 women aged 65─72 years enrolled in the Osteoporosis Risk Factor and Prevention-Fracture Prevention Study. Protein intake g/kg BW and g/d was calculated using a 3-day food record at baseline. At the 3-year follow-up, frailty phenotype was defined as the presence of three or more, and prefrailty as the presence of one or two, of the Fried criteria. At the 3-year follow-up, 36 women were frail and 206 women were prefrail. Higher protein intake ≥ 1.1 g/kg BW was associated with a lower likelihood of prefrailty (odds ratio = 0.45) and frailty (odds ratio = 0.09) when compared to protein intake of less than 1.1 g/kg BW at the 3-year follow-up. Women in the higher tertile of animal protein intake, but not plant protein, had a lower prevalence of frailty. Thus protein intake ≥ 1.1 g/kg BW and higher intake of animal protein may be beneficial to prevent the onset of frailty in older women.