Direct evaluation of the compliance with nutritional therapy is possible only in clinical trials while indirect methods such as self-reporting and interviews are used in clinical practice. Dietary history is the best method to evaluate nutritional habits in clinical practice; the same holds true for the compliance with low-protein diets in patients with chronic kidney disease. Other indexes to assess dietary compliance should be simple and easy to use in the clinical practice. Some of such functional and biological markers are blood urea nitrogen and serum phosphate levels (indirect markers of dietary intake), weight and body mass index (indirect markers of energy intake), and daily urinary excretion of nitrogen and sodium (indirect markers of protein and salt intake). The compliance with a low-protein diet in patients with chronic kidney disease is strongly influenced by psychosocial factors (e.g., satisfaction and comprehension), and thus by the supporting role of the physician and the dietitian, but also by the level of renal function and food characteristics. It must be pointed out that even a protein intake reduction of 0.2 g/kg/day improves blood urea nitrogen, phosphate levels, and acidosis.