Current issues of ACP Journal Club are published in Annals of Internal Medicine


Therapeutics

A low-protein diet slowed down the decline in renal function on inpatients with insulin-dependent diabetes and nephropathy

ACP J Club. 1991 Jan-Feb;114:13. doi:10.7326/ACPJC-1991-114-1-013


Source Citation

Brouhard BH, LaGrone L. Effect of dietary protein restriction on functional renal reserve in diabetic nephropathy. Am J Med. 1990;89:427-31.


Abstract

Objective

To evaluate the effect of a low-protein diet on functional renal reserve in patients with insulin-dependent diabetes mellitus and chronic renal disease.

Design

Randomized controlled trial with all patients followed for 1 year.

Setting

Patients were seen every 3 months and hospitalized for 1 or 2 days at the 3-, 6-, and 12-month visits to a clinical research center. [The referral pattern was not reported.]

Patients

15 patients with insulin-dependent diabetes mellitus, nephropathy (microalbuminuria ≥ 30 µg/min), and retinopathy. Blood pressure was controlled at ≤ 140/90 mm Hg.

Intervention

Patients were randomized to a low-protein diet consisting of 0.6 g/kg body weight per day (n = 8) or their usual protein intake, 1.0 g/kg per day (n = 7). Compliance was monitored at visits by the patient's report and by review of menus.

Main outcome measures

Functional renal reserve was measured at each admission by glomerular filtration rate (GFR) through urine assay of insulin. Increases in GFR (GFR response) were determined over 3 hours as the patient consumed a standard red-meat meal including 80 g protein.

Main results

GFR (measured in mL/min/ 1.73 m) declined in both groups (the decline was not significant (vs 0 time) for the low-protein group) over the study period, but the mean value at 12 months was higher in the low-protein group; (71{95% CI 55 to 89}* compared with 47 (CI 28 to 66, P < 0.05). The unrestricted protein group's mean GFR response to the test high-protein meal declined (P < 0.05) over 12 months, whereas the low-protein group's mean response remained the same and was significantly higher than that of the usual protein group. At 12 months, the mean absolute increase in GFR from premeal levels was 27.8 {CI 20 to 36}* in the low-protein group compared with 3.7 (CI .04 to 7.0)* for the control group (P < 0.05).

Conclusion

A low-protein diet in insulin-dependent diabetic patients with nephropathy was associated with slowing of the decline in renal function over 12 months when compared with similar patients who ate their usual diet.

Sources of funding: Texas Methodist Foundation; Juvenile Diabetes Foundation International; National Institutes of Health.

Address for article reprint: Dr. B. H. Brouhard, Section of Pediatric Nephrology Hypertension, The Cleveland Clinic Foundation, One Clinic Center, 9500 Euclid Avenue, Cleveland, OH 44195, USA.

*Numbers calculated from data in article.


Commentary

Microalbuminuria (urinary albumin excretion at a level below that detectable by routine clinical testing) is the simplest and most sensitive predictor of later development of overt nephropathy in patients with insulin-dependent diabetes mellitus. Screening for microalbuminuria in patients with insulin-dependent diabetes mellitus is recommended because most patients with microalbuminuria will develop overt renal disease, which may be delayed by treatment of hypertension (best shown with angiotensin-converting enzyme inhibitors), improved glucose control, or a protein-restricted diet. This clinical trial adds to the evidence that severe restriction of dietary protein (to 0.6 g/kg body weight per day) is acceptable to the motivated patient and may help preserve renal function.

In this small trial, the treated group had lower blood pressure and glycated hemoglobin and less proteinuria at baseline than the control group; the lack of statistical significance between the experimental and comparison group at baseline is a function of the small sample size. The differential loss of glomerular function attributed to treatment could have been caused in part by an already more progressive disease in the comparison group. This shows the need for multiple measurements of the important attributes before randomization and the hazard of prescribing treatment based on this single trial. Nevertheless, the weight of the evidence suggests that protein restriction can delay overt nephropathy after microalbuminuria appears. Studies are needed to assess how microalbuminuria can be prevented.

Elizabeth Barrett-Connor, MD
University of CaliforniaSan Diego, California, USA