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FIGURE 7-4 Glomerular filtration rate, measured as inulin clearance, in four groups of subjects. Young NT: healthy subjects 26 ± 3 years of age with normal blood pressure. Elderly NT: healthy subjects 68 ± 7 years of age with normal blood pressure. Elderly HT: subjects 70 ± 6 years of age with hypertension but not receiving diuretics. Elderly with heart failure: subjects 69 ± 6 years of age with heart failure. Symbols: open circles, men; solid circles, women.

Source: Used with permission from Kidney International, 1997, 51:1196-1204.

the decline of renal function with age and that restriction of dietary protein might prevent this decline.

This recommendation cannot be supported for a number of reasons as pointed out in a recent review (Walser, 1992). First, caloric restriction is more effective in rats than is protein restriction in retarding the age-associated decline in renal function (Tapp et al., 1989). Furthermore, caloric restriction without protein restriction markedly retarded the progression of glomerulosclerosis. Rats prefer rations containing higher proportions of protein, and the earlier studies indicating that protein restriction retarded renal damage failed to monitor food intake.

Second, protein restriction tends to lower GFR rather than increase it. Lew and Bosch (1991) recorded the dependence of creatinine clearance on spontaneous protein intake in subjects aged 22 to 50 years and in subjects aged

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