Dietary Plant and Animal Protein Intake and Decline in Estimated Glomerular Filtration Rate Among Elderly Women

A 10-Year Longitudinal Cohort Study

Amélie Bernier-Jean; Richard L. Prince; Joshua R. Lewis; Jonathan C. Craig; Jonathan M. Hodgson; Wai H. Lim; Armando Teixeira-Pinto; Germaine Wong

Disclosures

Nephrol Dial Transplant. 2021;36(9):1640-1647. 

In This Article

Discussion

In this longitudinal analysis of 1374 older women followed for 10 years, we report an association between the consumption of plant-derived proteins and reduced age-related decline in kidney function, but no beneficial or adverse association of animal-derived protein with eGFR. The mean eGFR decline over 10 years was 6.4 mL/min/1.73 m2, which is significantly less than the 1.1 mL/min/1.73 m2/year observed in Canadian women with similar age and baseline kidney function.[23] Nevertheless, women with higher intakes of plant-derived protein still experienced a substantially slower rate of decline in eGFR of 1.2 mL/min/1.73 m2 fewer for each increase of 10 g of plant protein, one-third of the average daily intake. The protective association of plant-based protein with the slope of eGFR was independent of baseline CKD status, diabetes or HTN, each of which was associated with a substantially lower average eGFR.

These findings are supported by a cross-sectional analysis of diabetic patients and a study of younger Iranian subjects.[24,25] The 11-year longitudinal analysis of the Nurses' Health Study, a cohort similar to ours in terms of kidney function, identified nondairy animal protein to be associated with a greater change in eGFR of the magnitude of −1.2 mL/min/1.73 m2 per 10 g/day of intake.[11] They did not identify beneficial or adverse associations with the intake of vegetable protein. In a cohort of older males (80%) with a history of myocardial infarction, each increase of 0.1 g/kg ideal body weight in total protein intake was associated with a change in eGFR of −1.2 mL/min/1.73 m2, but no difference was observed between protein of plant versus animal sources.[26] In exploratory analyses, we found that protein from fruits, vegetables and nuts, representing 30% of the plant protein intake, was associated with a slower decline in eGFR. Thus, our findings may relate to other constituents of fruits, vegetables and nuts in addition to their protein content. Several previous studies support this hypothesis. An analysis of the Atherosclerosis Risk in Communities cohort found participants consuming the most vegetable protein sources to have a 24% (95% CI 9–36) lower risk of incident CKD compared with those consuming the least.[27] While not focussing on protein intake per se, healthy plant-based diets, such as the Mediterranean and Dietary Approaches to Stop Hypertension diets, which are likely to be rich in plant protein, have also been linked with lower incidences of CKD in younger individuals.[28–34]

In contrast, animal-derived protein in the relatively small amounts consumed in this population was not associated with the change in eGFR, other than for a possible greater decline in eGFR among participants with a baseline eGFR <60 mL/min/1.73 m2. It is important to note that the mean total protein intake in this cohort was 1.15 g/kg/day, which is less than the level of concern outlined in KDIGO guidelines of >1.3 g/kg/day. Therefore, insufficient exposure of the cohort to high protein intakes could have prevented us from observing a negative effect of animal protein. In comparison, in a younger Iranian population, participants consuming over seven times more the meat than the reference group had a 73% higher risk of developing CKD.[35]

Some potential limitations are evident. This is an observational study demonstrating an association rather than causality. Second, as in all epidemiological studies of nutrition, the particular effect of a nutrient cannot be separated from those of other constituents of that diet. Thus, the benefits of plant protein in general, and fruits, vegetables and nuts in particular, may be due to the other constituents of plant foods such nitrate- and sulfur-containing compounds that have been the focus of other studies in this cohort.[36,37] Third, food consumption questionnaires are subject to measurement errors that can lead to biased estimates of effect. The dietary assessment utilized in this study has been validated against weighted food records and included visual aids for portion sizes.[15] Finally, the evaluation of kidney function was limited to eGFR, assessed by creatinine clearance and cystatin C, and would have been improved by measurement of proteinuria.

Strengths include the focus on a substantial population of community-based older women, an increasing demographic worldwide. Second, while the rate of progression of kidney disease was slower than in other studies, 33% had CKD Stage 3 or higher at baseline, and 13% progressed to this category over 10 years. Third, we based our assessment of kidney function on both creatinine and cystatin C, which has been shown to be superior to a single marker, particularly in the elderly population at risk for muscle wasting.[20,38] Cystatin C is also less influenced by diet and protein intake than serum creatinine.[39] Finally, we assessed dietary intake and renal function at three time points over 10 years, and we used longitudinal mixed linear models, which are reliable statistical designs to assess the progression of eGFR through time.[40]

In conclusion, this study has identified a beneficial association between plant-based protein and eGFR that may be related to other compounds within plant foods. A patient-centered approach to dietary advice with a focus on the promotion of plant sources of dietary protein rather than restriction may be considered. Importantly, from a public health point of view, encouraging high intake of fruits, vegetables and nuts may prevent or slow renal deterioration in older women in addition to their benefit on other organ systems.

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