Protein-calorie malnutrition (PCMN) in patients suffering from chronic renal failure treated with a low-protein diet (LDP) is generally considered to be the major adverse effect of such a diet. One cause of PCMN might be that these protein-restricted diets do not supply enough energy, although all of them are supposed to provide at least 35 kcal/kg body weight (BW). In order to test this hypothesis, we analyzed the hypothetical protein and energy intake of a patient on different LPDs. The food intake of such a patient was simulated by analyzing the average composition of 28 complete daily menus. The daily menus simulating 9 dietary schedules (0.3 g protein/kg BW; n = 6; 0.6 g protein/kg BW; n = 3) were taken from 5 different German cookery books. Our analysis revealed that only 2 schedules supplied enough energy. All others were deficient in energy by about 500 kcal/day. The deficiency occurred to the same extent in schedules for diets providing 0.3 and 0.6 g of protein/day. Therefore we conclude that PCMN in patients on LPDs is often due to an insufficient energy supply. The use of less protein-restricted diets does not necessarily prevent PCMN, as also these diets may be low in calories. Thus the use of caloric supplements, e.g. wine or polysaccharides, and correct dietary counseling by a skilled dietitian are recommended.