Does Protein Intake Really Have No Influence on Sarcopenia? Important Clarifications are Needed

Dear Editor:

We read with interest the recently published cross-sectional comparative study by Shaaker and Davenport (2024) that evaluated the relationship between dietary intake (calculated by 48-hr food diary) and sarcopenia in 51 hemodialysis patients (52.9% male, mean age 60 years, sarcopenia 33.3%). The study found that sarcopenic and non-sarcopenic patients had comparable dietary protein intake (0.68 vs. 0.68 g/kg/day, p = .413). The study revealed that “lack of exercise” (defined as “little or no regular exercise”; odds ratio = 7.624, p = .035) was an independent risk factor for sarcopenia, but dietary protein intake was not (Shaaker & Davenport, 2024). This topic is clinically relevant and worthy of more discussion. Regarding the effects of protein intake and exercise on sarcopenia, a recent network meta-analysis has found that resistance exercise predominantly improves muscle mass, muscle strength, and physical function in old adults. Protein supplements offer additional benefits when combined with exercise, but the benefits are limited when protein is taken alone without being combined with exercise (Liao et al., 2024). For hemodialysis patients, a recent meta-analysis involving 541 patients from 9 randomized controlled trials found that resistance exercise significantly improves muscle mass, muscle function, walking ability, and serum albumin levels compared to the controls (Li et al., 2024). Additionally, a prospective observation study disclosed that nutritional supplementation with individualized amounts of protein and calories for 1 year mitigates the loss of skeletal muscle mass index and benefits the survival rate in 132 older patients (aged 65 years or more) undergoing hemodiafiltration (Silva et al., 2023).

Nevertheless, we were surprised to find that, in Shaaker et al.’s study, the indicator of protein intake, normalized protein catabolic rate (nPCR; 1.69 g/kg/day in all patients, including 1.56 and 1.83 g/kg/day in sarcopenic and non-sarcopenic patients, respectively), is significantly higher than the 1.0 to 1.2 g/kg/day of protein intake recommended by the 2020 updated KDOQI Guideline (Ikizler et al., 2020). This discrepancy is even more pronounced considering the real-world situation, which is often worse than the guideline recommendations (Saglimbene et al., 2021). Furthermore, the daily protein intake calculated by the food diary (0.68 g/kg/day in both sarcopenic and non-sarcopenic patients) is only 40% of that estimated by nPCR (1.56 and 1.83 g/kg/day in sarcopenic and non-sarcopenic patients, respectively), resulting in a significant 60% difference between food recall and urine test (Shaaker & Davenport, 2024). This 60% difference is higher than the data from a study that found a difference of 25% between protein intake estimated by a short food-recall questionnaire and 24-hr urinary urea-nitrogen excretion in 60 patients with stage 3 to 4 chronic kidney disease (Thanachayanont et al., 2023). Therefore, we raise two concerns: (1) Is there any error in food recall or nPCR? (2) If the nPCR is correct, sarcopenia is undoubtedly related to factors other than inadequate nutrition in a situation with such high protein intake. The authors should highlight this high protein intake situation to avoid misinterpretation by the readers. Since this paper provides excellent inspiration, we sincerely hope the authors can address these concerns and contribute valuable knowledge to the medical community.

Pei-Fang YinCamillian Saint Mary’s Hospital Luodong, Yilan, Taiwan (R.O.C.) Gulele DulivuwanCamillian Saint Mary’s Hospital Luodong, Yilan, Taiwan (R.O.C.) Chorng-Jer HwangCamillian Saint Mary’s Hospital Luodong; Yilan, Taiwan (R.O.C.) Chih-Kuang LiuCamillian Saint Mary’s Hospital Luodong, Yilan, Taiwan (R.O.C.) Fu-Jen Catholic University, New Taipei, Taiwan (R.O.C.) Hon-Kwong MaCamillian Saint Mary’s Hospital Luodong, Yilan, Taiwan (R.O.C.) Chih-Chung ShiaoCamillian Saint Mary’s Hospital Luodong, Yilan, Taiwan (R.O.C.)