In healthy obese adults, a low-carbohydrate high-protein diet for 24 months increases serum urea levels by up to 14.4% at 3 months and maintains an elevation of 8.2% at 24 months compared to a low-fat diet, reflecting increased protein metabolism without evidence of uremic toxicity or impaired renal clearance.

When a person eats more protein and fewer carbs, the liver breaks down the extra amino acids and makes more urea to remove the nitrogen waste. The kidneys respond by filtering blood more quickly, which pulls more urea into the urine and keeps it from building up too much in the blood. Even though urea levels go up, the kidneys are not damaged — they are just working harder to handle the extra waste.