Nitrogen balance studies in apparently healthy elderly people and those who are housebound

Metabolic balance studies (5 d) for nitrogen were carried out in twenty-four apparently healthy elderly people (age 69.7-85.6 years) and a heterogeneous group of twenty housebound elderly people (age 69.9-85.1 years) with chronic diseases. During the study all subjects ate self-selected diets, lived in their own homes and continued their normal daily activities. Seven of the housebound received meals-on-wheels 5 d/week. Healthy men and women had mean metabolizable energy intakes of 8.7 and 6.6 MJ/d respectively compared with 6.3 and 4.8 MJ/d in the housebound. The average energy content of the meals-on-wheels as delivered was 2.4 MJ per meal, of which 2.1 MJ were consumed. The healthy men and women had average daily protein intakes of 69.4 and 59.7 g respectively compared with 46.3 and 39.1 g in the housebound. Meals-on-wheels as supplied provided 19.4 g protein per meal, of which 16.2 g were consumed. Healthy subjects were in equilibrium for N balance (0 mmol/d) with a daily intake of 733 mmol, which was equivalent to 11.04 mmol N (0.97 g mixed protein)/kg body-weight per d. Housebound individuals were in negative N balance (-95 mmol/d) with an intake of 475 mmol/d, corresponding to 7.59 mmol N (0.67 g mixed protein)/kg body-weight per d. We were unable to determine in the present study whether the negative N balance observed in the housebound people was due to the relatively low N intake or the underlying disease condition.