Findings regarding dietary protein and frailty are inconsistent. This inconsistency may be attributed to variations in energy intake adequacy. We hypothesized that the prevalence of frailty in older adults with sufficient energy intake is inversely associated with the intake of total, animal, and plant proteins; however, in those with deficient energy intake, this association may not be observed.

This cross-sectional study included data of 5,768 adults aged ≥65 years from the Korea National Health and Nutrition Examination Survey 2014–2018. Frailty was assessed using a modified Cardiovascular Health Study frailty index. Protein intake was measured via a 24-h recall and analyzed using multivariable logistic regression.

In older adults with sufficient energy intake, frailty was inversely associated with the intake of total (odds ratio [OR], 0.67; 95% confidence interval [CI], 0.46–0.97; p = 0.032), animal (OR, 0.59; 95% CI, 0.43–0.82; p = 0.001), and plant proteins (OR, 0.68; 95% CI, 0.50–0.92; p = 0.043). In those with deficient energy intake, total and animal protein intake showed no significant associations with frailty, whereas plant protein intake was inversely associated with frailty.

Adequate energy intake appears essential for the protective effects of total and animal protein against frailty. Higher plant protein intake appears to confer benefits regardless of energy intake, highlighting its potential role in frailty prevention.