Protein toxicity
Protein toxicity with proteinuria can result in those with preexisting kidney disease, or those who have lost kidney function due to advanced age. For otherwise healthy people, consuming over 2.0 g/kg/d, the extra protein can become a stressful stimulus for the kidney.[1]
Those with kidney disease are advised to avoid consumption of protein if possible, as consuming them accelerates the problems (see Chronic renal failure#Signs and symptoms). Most of the problems stem from the accumulation of toxins and wastes from protein metabolism that aren't getting filtered out.
It must be noted that kidney function (along with everything else) naturally declines with age due to the gradual loss of nephrons (filters) in the kidney. Therefore, a 90 year old cannot safely consume the same amount of protein as a 20 year old.
The first sign of kidney problems begins with microalbuminuria.
Severe illness including death can occur with chronic renal failure.
Common causes of kidney disease include diabetes, heart disease and long term untreated high blood pressure, as well as abuse of aspirin.