Limits of adaptation to a diet low in protein in normal man: urea kinetics

1992 ◽  
Vol 83 (1) ◽  
pp. 103-108 ◽  
Author(s):  
M. Danielsen ◽  
A. A. Jackson
Keyword(s):  
Production Rate ◽  
Nitrogen Balance ◽  
Healthy Men ◽  
Nitrogen Pool ◽  
Low Protein ◽  
Urea Production ◽  
Urea Kinetics ◽  
Normal Man ◽  
Oral Doses ◽  
Protein Diets

1. Urea kinetics were measured using prime/intermittent oral doses of [15N15N]urea in six healthy men taking diets adequate in energy and containing either 74 or 30 g of protein/day. 2. On 74 g of protein/day, urea production (199 mg of N day−1 kg−1) was 121% of intake, with 60% of the urea produced being excreted in the urine and 40% being salvaged in the colon; 69% of the salvaged nitrogen was retained in the metabolic nitrogen pool. 3. Nitrogen balance was not maintained on 30 g of protein/day. There was a significant decrease in the urea production rate (123 mg of N day−1 kg−1) and 54% of production was excreted in urine, with 46% being salvaged. 4. The pattern of urea production and salvaging on 30 g of protein/day was different to that seen in an earlier study on 35 g of protein/day, with a significant decrease in both production (71%) and salvaging (50%). 5. These data reinforce the conclusions drawn from an earlier study, that the salvaging of urea nitrogen by the colon is an integral part of the process of adaptation to low protein diets. The salvage system appears to fail on an intake of 30 g of protein/day and nitrogen is no longer conserved in sufficient amounts for balance to be maintained. 6. The changes seen in urea kinetics reinforce the conclusion based upon nitrogen balance that the minimum physiological requirement for protein in normal adult man lies between 30 and 35 g of protein/day.

Adaptation to a diet low in protein: effect of complex carbohydrate upon urea kinetics in normal man

1992 ◽  
Vol 82 (2) ◽  
pp. 191-198 ◽  
Author(s):  
M. Langran ◽  
B. J. Moran ◽  
J. L. Murphy ◽  
A. A. Jackson
Keyword(s):  
The Body ◽  
Protein Diet ◽  
Low Protein Diet ◽  
Urea Nitrogen ◽  
Low Protein ◽  
Urea Production ◽  
Urea Kinetics ◽  
Normal Man ◽  
Faecal Weight ◽  
Formula Diets

1. Urea kinetics were measured by using prime/intermittent oral doses of [15N15N]urea in five healthy men taking formula diets adequate in energy and containing either 70 or 35 g of protein/day. In some studies the low-protein diet was supplemented with non-starch polysaccharides in the form of ispaghula husk or ripe bananas. 2. On the 70 g of protein/day diet urea production was 132% of intake. Only 54% of the urea produced was excreted in the urine with 46% being salvaged in the colon; 90% of the salvaged nitrogen was retained in the metabolic nitrogen pool. 3. On the 35 g of protein/day diet the small decrease in urea production rate compared with that on the 70 g of protein/day diet was not significant, but only 36% of the urea produced was excreted in urine, with the majority, 64%, being salvaged. 4. The extent of urea-nitrogen salvaging on the 35 g of protein/day diet was similar in magnitude to the decrease in nitrogen intake, with the effect that the sum of intake and salvaged nitrogen did not differ between the 35 and the 70 g of protein/day diets. This implies that quantitative control is exerted over the rate at which urea nitrogen is salvaged. 5. The addition of non-starch polysaccharides to the 35 g of protein/day diet had a demonstrable effect upon faecal weight and composition, but did not exert any significant influence upon urea kinetics. 6. It is concluded that large changes in the rate of urea production are not necessary for adaptation to a low-protein diet, rather the salvaging of urea nitrogen in the lower bowel appears to be an important mechanism through which the body adapts to a low-protein diet. The salvaging of urea nitrogen by the colon makes an important contribution to the conservation of body nitrogen.

Nitrogen balance in barrows fed low-protein diets supplemented with essential amino acids

2007 ◽  
Vol 109 (1-3) ◽  
pp. 220-223 ◽  
Author(s):  
D. Deng ◽  
R.L. Huang ◽  
T.J. Li ◽  
G.Y. Wu ◽  
M.Y. Xie ◽  
...  
Keyword(s):  
Amino Acids ◽  
Nitrogen Balance ◽  
Essential Amino Acids ◽  
Low Protein ◽  
Protein Diets

scholarly journals Nitrogen balance of starting barrow pigs fed on increasing lysine levels

2004 ◽  
Vol 47 (1) ◽  
pp. 85-91 ◽  
Author(s):  
Ivan Moreira ◽  
Alessandro Luis Fraga ◽  
Diovani Paiano ◽  
Gisele Cristina de Oliveira ◽  
Cláudio Scapinello ◽  
...  
Keyword(s):  
Nitrogen Balance ◽  
Nitrogen Retention ◽  
Nitrogen Excretion ◽  
Protein Utilization ◽  
Urea Nitrogen ◽  
Plasma Urea ◽  
Low Protein ◽  
Feed Protein ◽  
Protein Diets ◽  
Net Protein

The effects of increasing lysine levels on nitrogen balance of pigs fed on low protein diets were evaluated. Four treatments (diets) containing lysine levels (0.8, 1.0 1.2 and 1.4%) were applied to 12 starting (20.0 ± 1.8 kg) barrow pigs. Methionine, threonine and tryptophan were kept constant to the lysine ratio in all diets. Feces and urine were collected during a 5-day period. Nitrogen output in urine (NOU), total nitrogen output (TNO), nitrogen retention (NR), net protein utilization (NPU), biological value or feed protein (BVFP), urine urea nitrogen (UUN), and plasma urea nitrogen (PUN) were determined. PUN showed high negative correlations with BVFP (-0.84), NPU (-0.76), and NR (-0.78) and a positive correlation (0.79) to NOU. Lowest nitrogen excretion and the best use of diet protein were obtained with 1.1% total lysine level. PUN is efficient to indicate amino acid for pigs.

scholarly journals Urea kinetics in healthy women during normal pregnancy

1997 ◽  
Vol 77 (2) ◽  
pp. 165-181 ◽  
Author(s):  
Irene S. M. McClelland ◽  
Chandarika Persaud ◽  
Alan A. Jackson
Keyword(s):  
Protein Intake ◽  
Late Pregnancy ◽  
Normal Pregnancy ◽  
Urea Hydrolysis ◽  
Urea Excretion ◽  
Urea Production ◽  
Urea Kinetics ◽  
Normal Women ◽  
Oral Doses ◽  
Habitual Protein Intake

Urea kinetics were measured in normal women aged 22-34 years at weeks 16, 24 and 32 on either their habitual protein intake (HABIT.) or a controlled intake of 60 g protein/d (CONTROL), using primed-intermittent oral doses of [15N15N]urea and measurement of plateau enrichment in urinary urea over 18 h (ID) or a single oral dose of [15N15N]urea and measurement of enrichment of urea in urine over the following 48 h (SD). The intake of protein during HABIT-ID (80 g/d) was greater than that on HABIT-SD (71 g/d); urea production as a percentage of intake was significantly greater at week 16 for HABIT-ID than HABIT-SD, whereas urea hydrolysis at week 16 was greater for HABIT-SD than HABIT-ID and urea excretion at week 32 was greater for HABIT-ID than HABIT SD. The combined results for HABIT-ID and HABIT-SD showed a significant reduction in urea production at week 32 compared with week 24. Urea excretion decreased significantly from week 16 to week 24 with no further decrease to week 32 and urea hydrolysis was significantly greater at week 24 than either week 16 or week 32. Compared with HABIT, on CONTROL there was a decrease in urea production at week 16, and urea excretion was significantly reduced at week 16. For all time periods urea production was closely related to the sum of intake plus hydrolysis. Hydrolysis was greatest at week 24 and closely related to urea production. There was a significant inverse linear relationship overall for hydrolysis as a proportion of production and excretion as a proportion of intake. The results show that on HABIT N is more effectively conserved in mid-pregnancy through an increase in urea hydrolysis and salvage, and during late pregnancy through a reduction in urea formation. Lowering protein intake at any stage of pregnancy increased the hydrolysis and salvage of urea. The staging of these changes was later than that in pregnancy in Jamaica.

Methionine supplementation of milk proteins for preruminant lambs. I. Effect of protein concentration and source of carbohydrate on nitrogen balance

1975 ◽  
Vol 26 (4) ◽  
pp. 673 ◽  
Author(s):  
DM Walker ◽  
RD Kirk
Keyword(s):  
Nitrogen Balance ◽  
Milk Proteins ◽  
Sole Source ◽  
Optimum Level ◽  
Low Protein ◽  
Gross Energy ◽  
Methionine Supplementation ◽  
Protein Milk ◽  
Milk Replacers ◽  
Protein Diets

Forty-seven crossbred lambs, aged 2–5 days at the start of the experiment, were used in three experiments. In experiment 1 a supplement of DL-methionine significantly increased the nitrogen balances of lambs given low or medium protein milk replacers based on cows' milk proteins. In experiment 2 the optimum level of supplementation of a low protein diet with DL-methionine was determined. Although the nitrogen balances were significantly increased by the supplement, the actual nitrogen balances at equivalent intakes of gross energy and nitrogen were less than those in experiment 1. The low protein diets in the two experiments differed only in the source of carbohydrate: lactose in cxpcrimcnt 1; lactose + glucose in experiment 2. In the final experiment 24 lambs in a 2 x 2 factorial design were fed on low protein diets containing casein as the source of protein, and lactose or glucose as the sole source of carbohydrate, with or without a supplement of DL-methionine. There was no significant effect of the source of carbohydrate on nitrogen balance.

Measurement of urea kinetics in humans: a validation of stable isotope tracer methods

1984 ◽  
Vol 246 (6) ◽  
pp. E519-E527 ◽  
Author(s):  
D. E. Matthews ◽  
R. S. Downey
Keyword(s):  
Single Dose ◽  
Production Rate ◽  
Short Duration ◽  
The Body ◽  
Priming Dose ◽  
Plasma Urea ◽  
Isotope Tracer ◽  
Adult Men ◽  
Urea Production ◽  
Urea Kinetics

To define the importance of an accurate priming dose for measurement of urea production using a primed, short-duration (e.g., 4 h) infusion of labeled urea, [18O]- and [13C]ureas were infused simultaneously at two different prime-to-infusion (P/I) doses into five young adult men. The measured mean (+/-SE) urea production rates were 261 +/- 12 and 509 +/- 25 mumol X kg-1 X h-1 for P/I = 12.6-h and 5.0-h priming doses, respectively. In a second series of studies, a single dose of [18O]urea tracer was administered intravenously to four subjects, and the urea production rate was determined from the plasma urea tracer disappearance curve obtained over the following 6 h by fitting the data to a two-exponent curve. The mean urea production rate was 224 +/- 14 mumol X kg-1 X h-1. Because the fractional turnover of the body urea pool is slow, the priming dose strongly influences the "apparent" plasma urea enrichment plateau and, therefore, the measured urea production rate during short-duration infusions. Alternatively, the single-dose protocol can be applied to measure human urea production accurately in periods as short as 6 h.

Effect of l -glutamic acid supplementation on performance and nitrogen balance of broilers fed low protein diets

2015 ◽  
Vol 100 (3) ◽  
pp. 590-600 ◽  
Author(s):  
R. M. Bezerra ◽  
F. G. P. Costa ◽  
P. E. N. Givisiez ◽  
E. R. Freitas ◽  
C. C. Goulart ◽  
...  
Keyword(s):  
Glutamic Acid ◽  
Nitrogen Balance ◽  
Acid Supplementation ◽  
Low Protein ◽  
Protein Diets
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