The Impact of Protein Intake on Renal Function Decline in Women with Normal Renal Function or Mild Renal Insufficiency

18 March 2003 | Volume 138 Issue 6 | Pages 460-467

Background: In individuals with moderate to severe renal insufficiency, low protein intake may slow renal function decline. However, the long-term impact of protein intake on renal function in persons with normal renal function or mild renal insufficiency is unknown.

Objective: To determine whether protein intake influences the rate of renal function change in women over an 11-year period.

Design: Prospective cohort study.

Setting: Nurses' Health Study.

Participants: 1624 women enrolled in the Nurses' Health Study who were 42 to 68 years of age in 1989 and gave blood samples in 1989 and 2000. Ninety-eight percent of women were white, and 1% were African American.

Measurements: Protein intake was measured in 1990 and 1994 by using a semi-quantitative food-frequency questionnaire. Creatinine concentration was used to estimate glomerular filtration rate (GFR) and creatinine clearance.

Results: In multivariate linear regression analyses, high protein intake was not significantly associated with change in estimated GFR in women with normal renal function (defined as an estimated GFR 80 mL/min per 1.73 m²). Change in estimated GFR in this subgroup over the 11-year period was 0.25 mL/min per 1.73 m² (95% CI, –0.78 to 1.28 mL/min per 1.73 m²) per 10-g increase in protein intake; the change in estimated GFR was 1.14 mL/min per 1.73 m² (CI, –3.63 to 5.92 mL/min per 1.73 m²) after measurement-error adjustment for protein intake. In women with mild renal insufficiency (defined as an estimated GFR > 55 mL/min per 1.73 m² but <80 mL/min per 1.73 m²), protein intake was significantly associated with a change in estimated GFR of –1.69 mL/min per 1.73 m² (CI, –2.93 to –0.45 mL/min per 1.73 m²) per 10-g increase in protein intake. After measurement-error adjustment, the change in estimated GFR was –7.72 mL/min per 1.73 m² (CI, –15.52 to 0.08 mL/min per 1.73 m²) per 10-g increase in protein intake, an association of borderline statistical significance. High intake of nondairy animal protein in women with mild renal insufficiency was associated with a significantly greater change in estimated GFR (–1.21 mL/min per 1.73 m² [CI, –2.34 to –0.33 mL/min per 1.73 m²] per 10-g increase in nondairy animal protein intake).

Conclusions: High protein intake was not associated with renal function decline in women with normal renal function. However, high total protein intake, particularly high intake of nondairy animal protein, may accelerate renal function decline in women with mild renal insufficiency.

Editors' Notes Context Although dietary protein restriction appears to slow the decline in renal function among patients with moderate renal insufficiency, its effect on normal and mildly decreased renal function is unknown. Contribution Among women from the Nurses' Health Study with normal renal function, protein intake was not associated with decline in glomerular filtration rate (GFR). In women with mild renal insufficiency, high protein intake, particularly of nondairy animal origin, was associated with more rapid than expected decline in GFR. Implications High protein intake is associated with declining GFR among women with mild renal insufficiency. A causal connection has not been demonstrated. Additional studies are needed to show that reducing protein intake protects the kidney. –The Editors

 

Author and Article Information

From Brigham and Women's Hospital, Harvard Medical School; and Massachusetts General Hospital, Harvard School of Public Health, Boston, Massachusetts.

Acknowledgments: The authors thank the participants of the Nurses' Health Study. They also thank Elaine Coughlan for carefully reviewing the statistical programming and manuscript content, Sue Malspeis for helping with the programming necessary to perform the measurement-error adjustment, Diane Feskanich for helping to interpret the food composition tables, Melissa Francis for assisting with manuscript preparation, and Walter Willett for reviewing the manuscript and making helpful suggestions.

Grant Support: By the National Institutes of Health (T32DK0740, T32DK07791, DK52866, CA87969, and HL34594).

Potential Financial Conflicts of Interest: None disclosed.

Requests for Single Reprints: Eric L. Knight, MD, MPH, Channing Laboratory, Nurses' Health Study, 3rd Floor, 181 Longwood Avenue, Boston, MA 02115; e-mail, elknight{at}partners.org.

Current Author Addresses: Drs. Knight, Hankinson, and Curhan: Channing Laboratory, Department of Medicine, Harvard Medical School and Brigham and Women's Hospital, 181 Longwood Avenue, Boston, MA 02115.

Drs. Stampfer and Spiegelman: Department of Epidemiology, Harvard School of Public Health, 677 Huntington Avenue, Boston, MA 02115.

Author Contributions: Conception and design: E.L. Knight, G.C. Curhan.

Analysis and interpretation of the data: E.L. Knight, M.J. Stampfer, S.E. Hankinson, D. Spiegelman, G.C. Curhan.

Drafting of the article: E.L. Knight, G.C. Curhan.

Critical revision of the article for important intellectual content: E.L. Knight, M.J. Stampfer, S.E. Hankinson, D. Spiegelman, G.C. Curhan.

Final approval of the article: E.L. Knight, M.J. Stampfer, S.E. Hankinson, D. Spiegelman, G.C. Curhan.

Provision of study materials or patients: G.C. Curhan.

Statistical expertise: E.L. Knight, M.J. Stampfer, D. Spiegelman, G.C. Curhan.

Obtaining of funding: G.C. Curhan.

Administrative, technical, or logistic support: E.L. Knight, M.J. Stampfer, S.E. Hankinson.

Collection and assembly of data: E.L. Knight, S.E. Hankinson, G.C. Curhan.