Nitrogen Retention in Adult Man: A Possible Factor in Protein Requirements

Adaptation of protein metabolism in relation to limits to high dietary protein intake

“…It seems thus possible that an expansion of muscle protein mass would occur very slowly and might continue for periods in excess of 50 d. Fat-free mass was not reported, but urinary creatinine, as a measure of muscle mass, increased signi®cantly by 4% (Oddoye & Margen,1979), which is consistent with the 1%ad increase in muscle protein for 50 d predicted from the N balance. However, other studies have not detected signi®cant changes in urinary creatinine excretion, fat-free mass, or other measures of protein deposition (Fisher et al, 1967;Cheng et al, 1978;Tarnapolsky et al, 1992). Even during 12 weeks of resistance training in older subjects (Campbell et al, 1995) or 1 month of strength training in young adults (Lemon et al, 1992), no differences due to higher dietary protein could be detected in fat-free mass, urinary creatinine, and muscle size (by computerized tomography) and composition.…”

“…In experimental studies, investigators have used the term`high protein' for diets ranging from 1.8 gakgad ± 3.3 gakgad (Fisher et al, 1967;Allen et al, 1979;Fern et al, 1991;Price et al, 1994;Quevedo et al, 1994;Yang et al, 1986). However, in one notable study male volunteers consumed 8 gakgad ( $ 600 g proteinad) for 9 d (Calloway et al, 1971).…”

Mechanisms permitting nephrotic patients to achieve nitrogen equilibrium with a protein-restricted diet.

“…Data from mice, rats, dogs, and humans fed high nitrogen intakes have demonstrated the same phenomenon (40)(41)(42). For instance, when healthy adults were fed 26-34 grams N/d for 28 to 42 d, B N remained strongly positive (up to ϩ7.9 grams N/d), yet body weight and total body potassium did not increase to the degree predicted by the retained nitrogen (42). The mechanism(s) responsible for the apparent nitrogen retention during excess nitrogen intakes are not understood (38, 39).…”

“…Nitrogen balance was strongly positive during the HPD, particularly in the nephrotic patients, but the lack of an increase in body weight suggests that nitrogen retention was less than predicted from the B N measurements. Data from mice, rats, dogs, and humans fed high nitrogen intakes have demonstrated the same phenomenon (40)(41)(42). For instance, when healthy adults were fed 26-34 grams N/d for 28 to 42 d, B N remained strongly positive (up to ϩ7.9 grams N/d), yet body weight and total body potassium did not increase to the degree predicted by the retained nitrogen (42).…”

Interrelationship of the human intestinal flora and protein utilization

“…Only renal and intestinal pathways are involved (dermal losses being usually small and neglected) in output of N. This assumption has been challenged, or exceptions have been suspected, in several recent metabolic studies. Fisher, Brush, Griminger & Sostman (1967) could not retrieve the N of intakes over 15 g N/24 h in urine and stools of young adults, nor was it possible to prove that it was retained as tissue N. They suggested that it was stored as non-protein N. Deosthale, Vasantgadkar & Tulpule (1964) suggested that 'it may be possible that the intestinal flora associated with vegetable protein diets might favour the conversion of amides of vegetable origin into gaseous N, which might escape detection'. These authors experimented with high-calorie diets containing about 11 g N124 h. T h e most pertinent observations have been reported by Costa, Ullrich, Kantor & Holland (1968) who proved that excess N was present in the expired air of man and mice loaded up to high-calorie high-protein levels.…”