Applied nutritional investigationLong-term effects of moderate protein diet on renal function and low-grade inflammation in older adults with type 2 diabetes and chronic kidney disease
Introduction
Experimental animal models have demonstrated the beneficial effects of dietary protein restriction in delaying the progression of renal disease [1]. In fact, dietary protein restriction may retard the decline of renal function and alleviates uremic symptoms caused by the accumulation of phosphorus, sulphates, organic acids, and urea [2], [3]. It has been suggested that dietary protein restriction also may delay the need for dialysis therapy [4], and favors the correction of secondary hyperparathyroidism and metabolic acidosis [5]. However, data on dietary protein restriction are unclear. In a recent study with 112 patients with type 2 diabetes mellitus (T2DM) and overt nephropathy, it was reported that protein restriction was neither feasible nor efficacious. The authors reported that the prescribed protein intake in the low-protein diet group was not statistically different from the protein intake in the normal protein diet group. Thus, non-adherence to the prescribed dietary protein restriction may result in an underestimation of its beneficial effects, in this study [6]. In fact, adherence to dietary protein restriction also could affect depressive symptoms. We previously demonstrated that the reduction of a dietary protein restriction regimen, from 7 to 6 d/wk was associated with an improvement in depressive symptoms and health-related quality of life in older patients with T2DM [7]. Furthermore, it has been reported that a reduced protein intake has an antioxidant effect in chronic kidney disease (CKD) in animals and humans [8], [9]. In an animal study, dietary protein restriction appeared to ameliorate inflammation, suppress oxidative stress, and reduce proteinuria [10]. Additionally it has been reported that unsaturated lipids also might be linked to anti-inflammatory status [11]. In this regard, little data are available on the long-term effects of a moderate protein diet (MPD) restriction regimen in older adults. Thus, in this study, we evaluated the effects of an MPD regimen, after 36 mo, on the decline of renal function, low-grade inflammation, oxidative stress, proteinuria, and body composition in older patients with T2DM and CKD.
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Patient population
In the study protocol, 74 older patients with T2DM participated. All patients were clinically assessed with a medical history, physical examination, and routine laboratory tests. Eligibility criteria for all patients included age >65 y; CKD (stage G3b–G4 defined according to the Kidney Disease: Improving Global Outcomes classification) [12] and T2DM (defined according to American Diabetes Association) [13] for at least 15 y and treated by diet plus insulin injection. All participants had
Results
At baseline (T0), BMI, fat-free mass (FFM,) systolic blood pressure (SBP), diastolic blood pressure (DBP), glycated hemoglobin (Hb)A1c, serum creatinine, blood urea nitrogen (BUN), and urinary protein excretion were similar in both study groups and are reported in Table 1.
Discussion
In this study, we reported that, an MPD regimen (6 d/wk) in older patients with T2DM significantly reduced renal failure by 42% (5.7 versus 2.4 mL/min annually; P < 0.001). This beneficial effect is also associated with an improvement in low-grade inflammation, oxidative stress, and proteinuria. Additionally, the MPD did not affect either glycemic control or nutritional status, demonstrating its sustainability long-term.
The role of an MPD regimen in older adults is not clear. Dietary protein
Conclusions
The present findings suggest that, in older individuals with T2DM, an MPD restriction (providing about 0.7 g/kg per day, 6 d/wk) may be useful in the management of diabetic nephropathy. In fact, the MPD induced a significant reduction in decline of renal function, proteinuria, low-grade inflammation, and oxidative stress. Additionally, these results were not associated with changes in FFM or glycemic control. A limitation of the present study is represented by the sample size and larger, future
Acknowledgments
This work was supported by the Italian Regional Founds (prot. 5725 06/03/2009).
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