![[Feedback]](/icons/banner/feedbackACT.gif){kind=icon}
![[For Subscribers]](/icons/banner/subscriberACT.gif){kind=icon}
![[Archive]](/icons/banner/archiveACT.gif){kind=icon}
![[Search]](/icons/banner/searchACT.gif){kind=icon}
![[Contents]](/icons/banner/tocACT.gif){kind=icon}
|
|
|
|
|
||
Unité INRA de Nutrition Humaine et de Physiologie Intestinale, INA-PG, 75231 Paris Cédex 05, France and
*
Service de Gastroentérologie and
Laboratoire de Biochimie, Hôpital Avicenne, 93009 Bobigny, France
2To whom correspondence should be addressed.
ABSTRACT
The aim of this study was to follow the fate of dietary nitrogen to assess the postprandial utilization of purified milk protein and to determine the acute influence of energy nutrients. For this purpose, a [15N]-labeling dietary protein approach was used. Twenty-five subjects swallowed an ileal tube and ingested [15 N]-milk protein alone or supplemented with either milk fat or sucrose. The absorption and postprandial deamination of dietary protein was monitored for 8 h. Sucrose delayed the absorption of protein longer than fat, but the ileal digestibility did not differ among groups (94.5–94.8%). Sucrose, but not fat, significantly reduced the postprandial transfer of [15N]-milk nitrogen to urea. Consequently, the net postprandial protein utilization (NPPU) of milk protein calculated 8 h after meal ingestion was 80% when ingested either alone or supplemented with fat and was significantly greater with sucrose (NPPU = 85%). This study shows that energy nutrients do not affect the nitrogen absorption but modify the metabolic utilization of dietary protein in the phase of nitrogen gain. Our method provides information concerning the deamination kinetics of dietary amino acids and further allows the detection of differences of dietary protein utilization in acute conditions. The diet composition should be carefully considered, and protein quality must be determined under optimal conditions of utilization.
KEY WORDS: • protein quality • postprandial deamination • milk protein • energy nutrients • humans.
The nutritional quality of dietary protein is defined as the ability of
the protein to satisfy the physiologic nitrogen and amino acid
requirements and is usually evaluated from the protein nitrogen
deposition in adaptive conditions (Munro 1964
). The
classical approach uses the net protein utilization (NPU), which is
assessed from long-term nitrogen balance measurements in human subjects
adapted to increasing levels of protein (Millward and Pacy 1995
). Another approach to consider is the acute nitrogen
deposition during the postprandial phase, which is likely to be very
critical regarding the deposition of dietary protein in the tissue.
Indeed the diurnal cycle of feeding and fasting periods results in
postprandial dietary nitrogen gains and postabsorptive losses of body
proteins. Under these conditions, the NPU calculated as the daily gain
should be lower than the postprandial gain (Millward et al. 1974
). In addition, nitrogen deposition is influenced by diet
composition because the energy nutrients modify the digestive kinetics
as well as nitrogen metabolism. The nitrogen-sparing effect of
carbohydrate was especially documented in animals (Reeds et al. 1981
, Vazquez et al. 1988
) and in humans
(Sim et al. 1979
, Yang et al. 1986
),
whereas the role of fat remains less clear (McCargar et al. 1989
, Richardson et al. 1979
). Therefore, the
aim of this study was to measure the acute postprandial utilization of
dietary protein nitrogen in the repletion phase of the diurnal cycle
and to investigate whether the nature of the energy source
(carbohydrate or fat) may influence postprandial retention. We recently
used a method to measure the specific fate of
[15N]-labeled dietary nitrogen in the
postprandial phase that allowed for the determination of postprandial
retention (Gausserès et al. 1997
). In this study,
we followed the postprandial kinetics of
[15N]-labeled milk nitrogen distribution in the
intestine, blood and urine after ingestion of
[15N]-labeled milk protein alone or
supplemented with sucrose or fat in fasting humans.
MATERIALS AND METHODS
Subjects.
The study was performed on 25 healthy volunteers (14 men and 11 women) aged 29 ± 6 y (range 20–40 y) and with a body mass index (BMI)3of 22.4 ± 2.5 kg/m2. None of the subjects had taken any medication or suffered from gastrointestinal upsets before the study. The protocol was approved by the Ethical Committee of the Saint-Germain-en-Laye Hospital. All subjects gave informed consent before the study.
Diets.
The [15N]-labeling of milk was performed in the experimental farm of Grignon with the collaboration of P. Schmidely (Department of Animal Sciences, INA-PG, Grignon, France). Milk was [15N]-labeled by giving an oral dose of 50 g/d of ([15N]H4)2SO4 (10 atom % isotope enrichment, Euriso-top, Saint Aubin, France) to a lactating cow for 11 d. The milk collected each day was pooled, then defatted. Proteins were concentrated by diafiltration (UFP 1.1 m2 IRIS 3065 Rhône Poulenc, 40-kDa membranes). The concentrated proteins were lyophilized. The isotopic enrichment of concentrated milk proteins was 0.4870 atom % (AP). The volunteers were assigned to a test group corresponding to one of the three experimental diets, each containing 30 g of [15N]-labeled milk protein (295 mmol nitrogen). One diet was supplemented with 100 g of sucrose (PS) and another (PF) with 43 g of milk fat (36 g butter and 46 g cream). The energy content represented that of a small meal and was 2173 and 2152 kJ, respectively. The third diet (P) was not associated with any other nutrient and contained 502 kJ. There were nine volunteers in both the sucrose and the fat groups and seven in the protein group. Each diet was dissolved in water to obtain a final volume of 500 mL.
Experimental design.
The volunteers came to the hospital the day before the experiment and a
double lumen tube was introduced into the gastrointestinal tract. One
tube was used to perfuse a saline solution of phenol red as a
nonabsorbable marker of intestinal effluents; the other was used to
aspirate the ileal effluents. After the subjects fasted overnight, the
perfusion site in the ileum was located using radioscopy. A catheter
(Jelco, Johnson-Jonhson, Chapling, Chatenay Malabry, France) was placed
in a forearm vein for blood sampling. At t0, a
saline solution containing 400 mg/L of phenol red was perfused into the
ileum at a flow rate of 1 mL/min, as previously described
(Gausserès et al. 1997
). Phenol red was used as a
marker to calculate the flow rate of the intestinal effluents. After 30
min of ileal sample collecting, the subjects ingested one of the three
test meals. The ileal effluents were collected continuously on ice and
pooled at 30-min intervals for 8 h. They were immediately treated
with diisopropylfluorophosphate 1 mmol/L (Sigma, St Quentin Fallavier,
France) as a protease inhibitor and frozen at -20°C. Blood samples
were collected every 30 min for 2 h, then hourly for 6 h, and
the serum was separated from whole blood by centrifugation at 2500 x
g for 20 min. Urine was collected every 2 h for
8 h and was preserved by adding thymol crystal and paraffin and
stored at 4°C.
Analytical methods.
The phenol red concentrations were determined in the ileal effluent by
a spectrophotometric method, as previously described
(Gausserès et al. 1997
). Total urea in the urine
and serum as well as creatinine in the urine were determined by an
enzymatic method with the use of a Dimension Automate
(Dupont de Nemours, Les Ulis, France). Ammonia was measured in the
urine by using a Kone automate (Kone, Evry, France). Glucose was
measured in the plasma by a glucose oxidase method (kit Glucose GOD-DP,
Kone, Evry, France) and insulin was measured by a RIA method (kit
INSI-PR, Cis bio International, Gif-sur-Yvette, France).
Urinary urea and ammonia as well as plasma urea and free amino acids
were isolated on a Na/K form of a cation-exchange resin (Biorad Dowex
AG50-X8, mesh 100–200, Interchim, Montluçon, France). For
urinary ammonia extraction, 7 mL of urine was mixed with 2 mL of resin
for 15 min. The supernatant was kept and the resin containing urinary
ammonia was washed five times with distilled water. Two milliliters of
the supernatant was mixed with 2 mL of resin and incubated for 2 h
at 30°C in the presence of 20 µL of urease (Sigma). The resin
containing urinary urea-derived ammonia was then washed with distilled
water and stored at 4°C until isotopic determination. For serum amino
acids and urea extraction, the serum proteins were precipitated by
mixing 4 mL of serum with 100 mg of 5-sulfo-salicylic acid (Prolabo,
Paris, France). After centrifugation at 2400 x g for
25 min at 4°C, the supernatant was kept and buffered at pH 7. The
urea was isolated from free amino acids on 1 mL of resin in the
presence of 8 µL of urease. After incubation for 2 h at 30°C,
the supernatant containing free amino acids was removed and
lyophilized. The resin containing urea-derived ammonia from serum was
washed with distilled water and stored at 4°C. Before isotopic
determination, resins were eluted with
KH2SO4 (2.5 mmol/L). The
[15N]-enrichment was measured by isotopic ratio
mass spectrometry (Optima, Fisons Instruments, Manchester, UK) coupled
to the elemental analyzer (NA 1500 series 2, Fisons Instruments). A
calibrated nitrogen tank was used as the reference for the ratio
15N/14N. Total nitrogen in
the ileal effluents was measured on an elemental nitrogen analyzer with
atropina (Carlo Erba Instruments, Fisons, Arcueil, France) as a
standard, as previously described (Gausserès et al. 1997
).
Calculations.
The flow rate of the ileal effluents was calculated from the phenol red
concentration, as previously described (Mahé et al. 1996
).
The exogenous nitrogen present in ileal effluents
(Nexo-ileal) and in urine
(Nexo-urine) in the form of urea, ammonia or
total nitrogen was calculated, as previously described
(Gaudichon et al. 1994
):
 |
where Ntot is the amount of total nitrogen in the sample, APi and APd are the [15N]-enrichment of the sample and the diet, respectively, and AP0 is the natural enrichment.
Ntot in the urine was calculated with the assumption that the sum of nitrogen present in urea, ammonia and creatinine represented 95% of the total nitrogen.
The exogenous nitrogen present in the urea body pool was calculated
according to the following formula:
 |
where TBW is the total body water, Nurea
is the concentration of urea in the plasma and
APureai and APurea0 are the
[15N]-enrichment of the plasma urea during the
experiment and the natural enrichment of the plasma urea, respectively.
TBW was estimated using the equation of Watson et al. (1980)
.
The net postprandial protein utilization (NPPU) was calculated
according to the following formula:
 |
Statistical analysis.
The results were expressed as means with their SEM. Differences from the basal values within glucose and insulin kinetics were tested using t tests. Differences between groups were analyzed with a repeated-measures ANOVA by using a general linear models procedure and Tukey's studentized range test for differences at each time point (GLM, SAS/STAT 6.03, SAS Institute, Cary, NC).
RESULTS
[15N]-Milk protein nitrogen digestion.
Substantial amounts of exogenous nitrogen were recovered in the ileum
60 min after the ingestion of milk protein alone or supplemented with
either sucrose or fat (Fig. 1
). The kinetics of the cumulated recovery of ileal exogenous
protein were similar in subjects ingesting protein either alone (P) or
supplemented with fat (PF). In contrast, it was delayed in the case of
milk protein supplemented with sucrose (PS) and was significantly lower
between 180 and 270 min (P < 0.05). Nevertheless, the
amount of dietary nitrogen recovered over an 8-h period after meal
ingestion was 15.4 ± 1.6 mmol in the P group, 15.8 ± 1.5
mmol in the PS group and 16.9 ± 3 mmol in the PF group. These
values were not different (P > 0.05). The true
exogenous protein nitrogen digestibilities were 94.8 ± 0.6,
94.5 ± 1 and 94.6 ± 0.5% for P, PF and PS groups
(P > 0.05), respectively.
|
The free amino acid [15N]-enrichment was
measured in serum after meal ingestion (Fig. 2
). In the case of milk protein ingested alone, the maximum
[15N]-enrichment of free amino acids was
observed between 1 and 3 h after meal ingestion and was
0.3763 ± 0.0075 AP, whereas it occurred between 4 and 5 h
when protein was associated with sucrose and reached a value of
0.3779 ± 0.0008 AP. After ingestion of milk protein and fat, the
maximal enrichment occurred after 3 h (0.3754 ± 0.0007 AP)
and remained stable until 5 h. Significant differences between P
an PS groups were observed between 4 and 6 h. The PF value was
also lower than the PS value at 5 h. The concentrations of glucose
(Fig. 3A
) and insulin (Fig. 3
B) were also measured in plasma.
After ingestion of protein associated with sucrose, glycemia increased
significantly from 5 ± 0.3 mmol/L in basal conditions to 8 ± 0.6 mmol/L at 1 h and returned to the fasting level after
3 h. Insulinemia increased concomitantly and significantly to a
maximal value of 0.29 ± 0.2 pmol/L at 1 h 30 min and then
returned to a basal value (0.033 ± 0.015 pmol/L) at 4 h. In
volunteers ingesting milk protein alone, a slight but significant
elevation of insulin occurred at 30 min, whereas no elevation of blood
glucose was observed. In volunteers ingesting milk protein supplemented
with fat, no elevation of blood glucose or insulin was observed.
|
|
The amount of exogenous nitrogen present in the body urea pool was
significantly higher during the first 4 h after ingestion of milk
protein alone compared with that of subjects ingesting milk protein
supplemented with sucrose. However, no difference between groups was
observed after 4 h (Fig. 4A
). The amount of exogenous nitrogen excreted in the urine in the
form of urea was significantly lower over the 8-h urine collection
period in subjects receiving sucrose (PS group) compared with those
ingesting protein either alone or supplemented with fat (Fig. 4
B). The statistical analysis revealed a marked global
effect of meal on the whole urinary urea kinetics (P = 0.0003). The exogenous nitrogen recovered in the urinary urea after
8 h represented 23.2 ± 2.3, 23.3 ± 2.5 and 14.3
± 1.1 mmol in P, PF and PS groups, respectively. Under these
conditions, the kinetics of the transfer of exogenous nitrogen to urea
was calculated by adding the exogenous urea nitrogen excreted in the
urine to the exogenous nitrogen present in the body urea pool (Fig. 4
C). The deamination to urea was significantly lower in the
PS group than in the control group (protein alone) throughout the 8-h
experimental period (P = 0.0015). In subjects receiving
protein and fat, this transfer was significantly lower than in the
control group during the first 2 h but did not differ after 4 h. At the end of the experimental period, the amount of exogenous
nitrogen transferred to urea was significantly lower (P < 0.05) after ingestion of milk protein supplemented with sucrose
(27.7 ± 2.2 mmol) than after ingestion of milk protein alone
(41.7 ± 5.2 mmol) or supplemented with fat (42.3 ± 3.3
mmol). The urinary excretion of exogenous nitrogen in the form of
ammonia represented 1.1 mmol in all three groups 8 h after meal
ingestion and was not significantly different among the groups (not
shown).
|
The whole dietary protein deamination, i.e., the sum of exogenous
nitrogen present in blood urea and in all of the nitrogen fractions in
the urine (mainly urea, ammonia and creatinine), was 29.5 ± 2.3,
44.4 ± 4.6 and 42.7 ± 3.6 mmol after 8 h for PS, P and
PF groups, respectively. It was significantly lower (P < 0.05) for the group PS compared with the P and PF groups. The net
postprandial protein utilization (NPPU) of exogenous nitrogen,
calculated from the true ileal digestibility of nitrogen and the true
percentage of ingested nitrogen retained in the organism over an 8-h
period, was significantly higher (P < 0.05) for the PS
group compared with the P and PF groups (Table 1).
|
DISCUSSION
The objective of our study was to assess milk protein nitrogen retention during the postprandial repletion phase of the diurnal cycle and to evaluate the acute influence of energy nutrients, i.e., carbohydrate or fat, on this net postprandial protein utilization (NPPU) in humans. For this purpose, [15N]-nitrogen ileal digestibility and [15N]-urea production were assessed during the 8-h postprandial phase after the ingestion of a single dose of [15N]-labeled milk protein alone or supplemented with either sucrose or fat in healthy volunteers. The results showed a high NPPU value for milk protein. Under our experimental conditions, sucrose but not fat significantly improved the postprandial utilization of milk protein nitrogen in humans.
We first noted that the overall ileal digestibility of milk nitrogen
over the 8 h was not affected by sucrose or fat. The results
confirm previous results obtained with protein ingested in either a
purified (Mahé et al. 1996
) or nonpurified form
(Gaudichon et al. 1995
, Gausserès et al. 1997
) and indicate that milk protein presents a high ileal
digestibility of 95%. An interesting outcome of this study is that the
overall ileal digestibility was not affected by the presence of an
energy nutrient even with a high dose of protein (30 g). Nevertheless,
sucrose increased the oro-ileal transit time of exogenous nitrogen,
whereas fat had no observable effect at the ileal level. The slowing
effect of carbohydrate on the gastric emptying of the meal has been
well documented and could be due to both a control of the energy
content in the duodenum and to a higher viscosity (Houghton et al. 1987
, Hunt et al. 1985
, Maes et al. 1995
). Thus, the slower transit that we observed at the ileal
level should originate mainly from a delayed gastric emptying of the
meal subsequent to a higher energy density. The absence of any effect
in the presence of fat was more surprising because the energy density
is similar to that of the sucrose meal. However, our observation is
consistent with studies reporting that ingestion of fat in a liquid
form (oil or butter) results in its remaining at the top of the gastric
chyme and emptying after the aqueous phase of the meal (Jian et al. 1982
, Meyer et al. 1986
). Our ileal results
were further confirmed by the appearance of
[15N]-amino acids in the plasma. Although some
amino acids are metabolized in the liver, especially alanine and
glutamine, others such as branched-chain amino acids are poorly
catabolized, and it is assumed that the enrichment kinetics of serum
amino acids reflect in part the intestinal absorption kinetics. The
maximal [15N]-enrichment of the plasma amino
acid fraction was observed later in the presence of sucrose than in the
presence of fat or when milk protein was ingested alone. The absence of
peaks in the fat group could be due to a slightly slower digestive
transit not detectable at the ileal site.
Another important aspect of this study is the evaluation of the level
of postprandial deamination of the ingested protein. The level of
exogenous nitrogen excretion after a single meal is dependent on the
time after ingestion, including a first-pass deamination of the dietary
protein in the splanchnic area as well as subsequent slower elimination
of dietary nitrogen from a more complex metabolic fate. According to
our kinetics of ileal nitrogen flow rates, plasma amino acid appearance
and urea production, the first splanchnic pass of the dietary nitrogen
appeared to be nearly complete in the 6–8 h after meal ingestion.
During this period, insulin also returned to its basal value. Under
those conditions, the deamination of milk protein was 15, 13.8 and 10%
of the absorbed nitrogen in the 8 h after ingestion of the protein
alone or supplemented with fat or sucrose, respectively. Few data are
available concerning the fraction of dietary protein and those of the
different amino acids oxidized during the postprandial phase. The
oxidation of [13C]-leucine milk was assessed at
31% in the 7 h after meal ingestion (Boirie et al. 1996
). Nevertheless, the dietary leucine oxidation does not
reflect the oxidation of all of the dietary amino acids because amino
acids exhibit different regulatory levels with regard to oxidative
pathways. In humans receiving increasing levels of protein intake,
leucine oxidation significantly increases, whereas lysine catabolism
remains constant (Zello et al. 1992
). This suggests that
essential amino acids respond differently to identical metabolic
conditions. This is of particular importance when protein is
administered in acute doses to fasting volunteers because
branched-chain amino acids play an important role in the energy
production pathways. Those considerations emphasize the necessity of an
intrinsic tracer sufficiently representative of the dietary protein to
assess its postprandial utilization.
The nitrogen sparing effect of sucrose is well documented and is
assumed to be due to both a lesser entry of amino acids into the energy
production pathways and to the anabolic effect of insulin (Motil et al. 1981
, Munro 1964
). In subjects
intraduodenally infused with amino acids, glucose was demonstrated to
reduce the splanchnic uptake of the dietary leucine and glucose
production as well as body leucine oxidation (Krempf et al. 1993
). In addition to this reduced neoglucogenic amino acid
uptake, glucose also induced insulin secretion. This was not the case
when protein was ingested alone, although an insulin effect of some
amino acids was reported (Nutall and Gannon 1990
). The
anabolic drive of insulin on protein, especially on muscle, was
controvertibly attributed both to an inhibition of protein breakdown
and to a stimulation of protein synthesis (De Feo 1996
,
Millward et al. 1990). In the case of fat, the
deamination was reduced at first but then did not differ from the group
receiving the protein alone. This probably originates from the fact
that fat neither stimulates insulin secretion nor participates in the
neoglucogenic metabolism. Our results are consistent with the idea that
under postprandial conditions, glucose acts as a fuel that is used up
first by the organism, whereas fat is mainly transported to the
adipocytes and then slowly mobilized. However, confusing results were
reported in the literature concerning the interaction between fat and
nitrogen metabolism. In obese subjects, the consumption of a
carbohydrate diet substantially decreased both the rate of leucine
oxidation and the urinary N excretion, in contrast to a fat diet
(Vazquez et al. 1985
). The same authors reported later
that, in rats, fat played a role in nitrogen sparing, even if this role
was not as effective as that of glucose (Vazquez et al. 1988
). The opposite conclusions of Richardson et al. (1979)
and
McCargar et al. (1989)
offer another illustration of these
discrepancies; in similarly designed studies, subjects were adapted to
a diet containing fat and carbohydrates in a ratio of either 1:1 or
1:2. Richardson et al. reported a greater N balance with the high
carbohydrate diet and McCargar et al. found the contrary. It was
suggested that the effect of the energy nutrients on nitrogen
metabolism also depended on the level of energy intake. Although these
studies concerning nitrogen retention in a long-term experiment are not
comparable to ours, they nevertheless illustrate how the specific
effect of fat remains unclear.
The present results indicated a high NPPU value of 80–85% for milk
protein nitrogen measured in the 8 h after meal ingestion. The
protein quality could be defined as the ability of the protein to
satisfy the physiologic amino acid requirements, but the criteria by
which to assess this quality are still under discussion. The protein
digestibility-corrected amino acid score (PD-CAAS), as recommended by
the FAO, takes into account both the amino acid composition and the
digestibility of the protein (FAO/WHO 1990
). Other
criteria focusing on the metabolic fate of protein have been used and
appear to be very accurate when discriminating between the quality of
different proteins, but few values of protein retention are available
in humans. In a long-term study conducted among Nigerian women, the NPU
of a beef protein–based meal, assessed as the slope relating the daily
N balance to increasing protein intake, was 55% (Egun and Atinmo 1993
). However, this low value does not reflect the
postprandial retention of the protein because it averages the N balance
in both the gain and depletion phases. Stating that the calculation of
the postprandial utilization should give separate consideration to the
balance regression during the repletion and depletion phases, Price et al. (1994)
reported a mean PPU value of 80–85% for milk protein. As a
comparison, in another study using the same
[15N]-labeling protein method, a NPPU of 73%
was obtained in the 8 h after ingestion of
[15N]-labeled pea protein in the form of pea
flour, i.e., in the presence of starch (Gausserès et al. 1997
). Under these conditions, the NPPU of pea protein must be
compared with the value obtained with milk protein added to sucrose
(i.e., 85%) rather than to the NPPU obtained with purified milk
protein (i.e., 80%). Moreover, the carbohydrate source should also be
considered because it influences the insulin responses. The glycemic
index of sucrose and lactose is 65 and 57, respectively, whereas that
of starches is highly variable and depends in part on the composition
of amylose and amylopectin (Behall et al. 1988
). The
influence of fiber on insulinemia should also be considered; it raises
a methodological question concerning whether the protein retention must
be studied with the protein in its original food or administered in a
purified form and supplemented with a controlled quantity and quality
of energy-containing nutrients.
In conclusion, we showed that the direct measurement of
[15N]-labeled dietary amino acid deamination in
the postprandial phase allows the detection of differences in dietary
protein quality. This technique is rapid because it may be used without
any adaptation period to diet and it indicates the kinetics of
exogenous nitrogen distribution after a meal. Although the contribution
of oxidation to the circulating amino acid disappearance is lower than
that of anabolic pathways (Boirie et al. 1996
), it
nevertheless reflects the influence of dietary factors on the metabolic
fate of dietary protein. The significant improvement due to the
addition of sucrose must be taken into account because the variation in
retention values of several proteins is not extremely large. Under
these conditions, the value of 85% should be considered for milk
protein NPPU when calculated in the 8 h after meal ingestion.
ACKNOWLEDGMENTS
We are indebted to Arilait Recherches for their constructive scientific discussion. L. Vassal and M. Pitel (INRA, Station de Recherches Laitières, Jouy-en-Josas, France) are gratefully acknowledged for the purification of [15N]-labeled milk protein. We thank M. Deyra from the Gastroenterology Unit for her skillful clinical assistance as well as M. Desmons and J. Miquel from the Biochemistry Laboratory of Avicenne Hospital (Bobigny, France).
FOOTNOTES
1 Supported by Arilait Recherches and the Institut
Français pour la Nutrition, Paris, France. 
2 Abbreviations used: BMI, body mass index; NPPU,
net postprandial protein utilization; NPU, net protein utilization; P,
milk protein group; PD-CAAS, protein digestibility-corrected amino acid
score; PF, milk protein group + fat; PS, milk protein group + sucrose;
TBW, total body water.
Manuscript received September 6, 1998. Initial review completed October 15, 1998. Revision accepted December 15, 1998.
REFERENCES
1.
Behall K. M., Schofiled D. J., Canary J. Effect of starch structure on glucose and insulin responses in adults. Am. J. Clin. Nutr. 1988;47:428-432
2.
Boirie Y., Gachon P., Corny S., Fauquant J., Maubois J. L., Beaufrère B. Acute postprandial changes in leucine metabolism as assessed with an intrinsically labeled milk protein. Am. J. Physiol. 1996;271:E1083-E1091
3. De Feo P. Hormonal regulation of human protein metabolism. Eur. J. Endocrinol. 1996;135:7-18[Abstract]
4. Egun G. N., Atinmo T. Protein requirement of young adult Nigerian females on habitual Nigerian diet at the usual level of dietary intake. Br. J. Nutr. 1993;70:439-448[Medline]
5. FAO/WHO (1990) Report on the Joint FAO/WHO Expert Consultation on Protein Quality Evaluation. Food and Agriculture Organization of the United Nations, Rome, Italy.
6. Gaudichon C., Mahé S., Roos N., Benamouzig R., Luengo C., Huneau J. F., Sick H., Bouley C., Rautureau J., Tomé D. Exogenous and endogenous nitrogen flow rates and level of protein hydrolysis in the human jejunum after [15N] milk and [15N] yoghurt ingestion. Br. J. Nutr. 1995;74:251-260[Medline]
7. Gaudichon C., Roos N., Mahé S., Sick H., Bouley C., Tomé D. Gastric emptying regulates the kinetics of nitrogen absorption from 15N-Labeled milk and 15N-Labeled yogurt in miniature pigs. J. Nutr. 1994;24:1970-1977
8.
Gausserès N., Mahé S., Benamouzig R., Luengo C., Ferrière F., Rautureau J., Tomé D. [15N]-Labeled pea flour protein nitrogen exhibits good ileal digestibility and postprandial retention in humans. J. Nutr. 1997;127:1160-1165
9. Houghton L.A, Hickson K., Read N. W. Effect of food consistency on gastric emptying in man. Gut 1987;28:1587-1588
10. Hunt J. N., Smith J. L., Jian C. L. Effect of meal volume and energy density on the gastric emptying of carbohydrates. Gastroenterology 1985;89:1326-1330[Medline]
11. Jian R., Vigneron N., Najean Y., Bernier J. J. Gastric emptying and intragastric distribution of fats in man. A new scintigraphic method of study. Dig. Dis. Sci. 1982;27:705-711[Medline]
12.
Krempf M., Hoerr R. A., Pelletier V. A., Marks L. M., Gleason R., Young V. R. An isotopic study of the effect of dietary carbohydrates on the metabolic fate of dietary leucine and phenylalanine. Am. J. Clin. Nutr. 1993;57:161-169
13.
Maes B. D., Ghoos Y. F., Geypens B. J., Hiele M. I., Rutgeerts P. J. Relation between gastric emptying rate and energy intake in children compared with adults. Gut 1995;36:183-188
14.
Mahé S., Roos N., Benamouzig R., Davin L., Luengo C., Gagnon L., Gausserès N., Rautureau J., Tomé D. Gastrojejunal kinetics and the digestion of [15N]ß-lactoglobulin and casein in humans: the influence of the nature and quantity of the protein. Am. J. Clin. Nutr. 1996;63:546-552
15.
McCargar L. J., Clandinin M. T., Belcastro A. N., Walker K. Dietary carbohydrates-to-fat ratio: influence on whole-body nitrogen retention, substrate utilization, and hormone response in healthy male subjects. Am. J. Clin. Nutr. 1989;49:1169-1178
16. Meyer J. H., Mayer E. A., Jehn D., Guy Fink A. S., Fried M. Gastric processing and emptying of fat. Gastroenterology 1986;90:1176-1187[Medline]
17. Millward D. J., Nnanyelugo D. O., James W.P., T & Garlick P. J. Protein metabolism in skeletal muscle: the effect of feeding and fasting on muscle RNA, free amino acids, and plasma insulin concentrations. Br. J. Nutr. 1974;32:127-142[Medline]
18. Millward D. J., Pacy P. J. Postprandial protein utilization and protein quality assessment in man. Clin. Sci. (Lond.) 1995;88:597-606[Medline]
19. Millward D. J. The hormonal control of protein turnover. Clin. Nutr. 1990;9:115-126
20.
Motil K. J., Bier D. M., Matthews D. E., Burke J. F., Young V. R. Whole body leucine and lysine metabolism studied with [1-13C]leucine and [
-15N]lysine: response in healthy young men given excess energy intake. Metabolism 1981;30:783-791[Medline]
21. Munro H. N. General aspects of the regulation of protein metabolism by diet and by hormones. Munro H.N. Allison J.B. eds. Mammalian Protein Metabolism 1964:381-481 Academic Press New York, NY.
22. Nuttall F. Q., Gannon M. C. Metabolic response to egg white and cottage cheese protein in normal subjects. Metabolism 1990;39:749-755[Medline]
23. Price G. M., Halliday D., Pacy P. J., Quevedo M. R., Millward D. J. Nitrogen homeostatis in man: influence of protein intake on the amplitude of diurnal cycling of body nitrogen. Clin. Sci. (Lond.) 1994;86:91-102[Medline]
24. Reeds P. J., Fuller M. F., Cadenhead A., Lobley G. E., McDonald J. D. Effects of changes in the intakes of protein and non-protein energy on whole-body protein turnover in growing pigs. Br. J. Nutr. 1981;45:539-546[Medline]
25.
Richardson D. P., Wayler A. H., Scrimshaw N. S., Young V. R. Quantitative effect of an isoenergetic exchange of fat for carbohydrates on dietary protein utilization in healthy young men. Am. J. Clin. Nutr. 1979;32:2217-2226
26. Sim A.J.W, Young V. R., Wolfe B. M., Clarke D., Moore F. D. Glucose promotes whole-body protein synthesis from infused amino acids in fasting man. Lancet 1979;13:68-72
27. Vazquez J. A., Morse E. L., Adibi S. A. Effect of dietary fat, carbohydrate, and protein on branched-chain amino acid catabolism during caloric restriction. J. Clin. Investig. 1985;76:737-743
28. Vazquez J. A., Paul H. S., Adibi S. A. Regulation of leucine catabolism by caloric sources. J. Clin. Investig. 1988;82:1606-1613
29.
Watson P.E, Watson I. D., Batt R. D. Total body water volumes for adult males and females estimated from simple anthropometric measurements. Am. J. Clin. Nutr. 1980;33:27-39
30.
Yang R. D., Matthews D. E., Bier D. M., Wen Z. M., Young V. R. Response of alanine metabolism in humans to manipulation of dietary protein and energy intakes. Am. J. Physiol. 1986;250:E39-E46
31. Zello G. A., Telch J., Clarck R., Ball R. O., Pencharz B. P. Reexamination of protein requirements in adult male humans by end product measurements of leucine and lysine metabolism. J. Nutr. 1992;122:1000-1008
This article has been cited by other articles:
|
|
 |
|
  B. Juillet, H. Fouillet, C. Bos, F. Mariotti, N. Gausseres, R. Benamouzig, D. Tome, and C. Gaudichon Increasing habitual protein intake results in reduced postprandial efficiency of peripheral, anabolic wheat protein nitrogen use in humans Am. J. Clinical Nutrition, March 1, 2008; 87(3): 666 - 678. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. W. Schaart, A. C. J. M. de Bruijn, D. Tibboel, I. B. Renes, and J. B. van Goudoever Dietary Protein Absorption of the Small Intestine in Human Neonates JPEN J Parenter Enteral Nutr, November 1, 2007; 31(6): 482 - 486. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. A. Humayun, R. Elango, S. Moehn, R. O. Ball, and P. B. Pencharz Application of the Indicator Amino Acid Oxidation Technique for the Determination of Metabolic Availability of Sulfur Amino Acids from Casein versus Soy Protein Isolate in Adult Men J. Nutr., August 1, 2007; 137(8): 1874 - 1879. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C. Bos, G. Airinei, F. Mariotti, R. Benamouzig, S. Berot, J. Evrard, E. Fenart, D. Tome, and C. Gaudichon The Poor Digestibility of Rapeseed Protein Is Balanced by Its Very High Metabolic Utilization in Humans J. Nutr., March 1, 2007; 137(3): 594 - 600. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. Lacroix, C. Bos, J. Leonil, G. Airinei, C. Luengo, S. Dare, R. Benamouzig, H. Fouillet, J. Fauquant, D. Tome, et al. Compared with casein or total milk protein, digestion of milk soluble proteins is too rapid to sustain the anabolic postprandial amino acid requirement. Am. J. Clinical Nutrition, November 1, 2006; 84(5): 1070 - 1079. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Y. C. Luiking, N. E. P. Deutz, M. Jakel, and P. B. Soeters Casein and Soy Protein Meals Differentially Affect Whole-Body and Splanchnic Protein Metabolism in Healthy Humans J. Nutr., May 1, 2005; 135(5): 1080 - 1087. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C. Bos, B. Juillet, H. Fouillet, L. Turlan, S. Dare, C. Luengo, R. N'tounda, R. Benamouzig, N. Gausseres, D. Tome, et al. Postprandial metabolic utilization of wheat protein in humans Am. J. Clinical Nutrition, January 1, 2005; 81(1): 87 - 94. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. B. Soeters, M. C. G. van de Poll, W. G. van Gemert, and C. H. C. Dejong Amino Acid Adequacy in Pathophysiological States J. Nutr., June 1, 2004; 134(6): 1575S - 1582S. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
V. E. Baracos Animal Models of Amino Acid Metabolism: A Focus on the Intestine J. Nutr., June 1, 2004; 134(6): 1656S - 1659S. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C. Morens, C. Bos, M. E. Pueyo, R. Benamouzig, N. Gausseres, C. Luengo, D. Tome, and C. Gaudichon Increasing Habitual Protein Intake Accentuates Differences in Postprandial Dietary Nitrogen Utilization between Protein Sources in Humans J. Nutr., September 1, 2003; 133(9): 2733 - 2740. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. J. Reeds and P. J. Garlick Protein and Amino Acid Requirements and the Composition of Complementary Foods J. Nutr., September 1, 2003; 133(9): 2953S - 2961. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C. Bos, C. C. Metges, C. Gaudichon, K. J. Petzke, M. E. Pueyo, C. Morens, J. Everwand, R. Benamouzig, and D. Tome Postprandial Kinetics of Dietary Amino Acids Are the Main Determinant of Their Metabolism after Soy or Milk Protein Ingestion in Humans J. Nutr., May 1, 2003; 133(5): 1308 - 1315. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. V. Kurpad and V. R. Young What Is Apparent Is Not Always Real: Lessons from Lysine Requirement Studies in Adult Humans J. Nutr., April 1, 2003; 133(4): 1227 - 1230. [Full Text] [PDF]
|
|
|
|
|
|
H. Fouillet, C. Bos, C. Gaudichon, and D. Tome Approaches to Quantifying Protein Metabolism in Response to Nutrient Ingestion J. Nutr., October 1, 2002; 132(10): 3208S - 3218. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J.-C. Bouthegourd, P. C. Even, D. Gripois, B. Tiffon, M.-F. Blouquit, S. Roseau, C. Lutton, D. Tome, and J.-C. Martin A CLA Mixture Prevents Body Triglyceride Accumulation without Affecting Energy Expenditure in Syrian Hamsters J. Nutr., September 1, 2002; 132(9): 2682 - 2689. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. A. L. Calbet and D. A. MacLean Plasma Glucagon and Insulin Responses Depend on the Rate of Appearance of Amino Acids after Ingestion of Different Protein Solutions in Humans J. Nutr., August 1, 2002; 132(8): 2174 - 2182. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
H. Fouillet, F. Mariotti, C. Gaudichon, C. Bos, and D. Tome Peripheral and Splanchnic Metabolism of Dietary Nitrogen Are Differently Affected by the Protein Source in Humans as Assessed by Compartmental Modeling J. Nutr., January 1, 2002; 132(1): 125 - 133. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 C. Morens, C. Gaudichon, G. Fromentin, A. Marsset-Baglieri, A. Bensaid, C. Larue-Achagiotis, C. Luengo, and D. Tome Daily delivery of dietary nitrogen to the periphery is stable in rats adapted to increased protein intake Am J Physiol Endocrinol Metab, October 1, 2001; 281(4): E826 - E836. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
H. Fouillet, C. Gaudichon, F. Mariotti, C. Bos, J. F. Huneau, and D. Tome Energy nutrients modulate the splanchnic sequestration of dietary nitrogen in humans: a compartmental analysis Am J Physiol Endocrinol Metab, August 1, 2001; 281(2): E248 - E260. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. Daenzer, K. J. Petzke, B. J. Bequette, and C. C. Metges Whole-Body Nitrogen and Splanchnic Amino Acid Metabolism Differ in Rats Fed Mixed Diets Containing Casein or Its Corresponding Amino Acid Mixture J. Nutr., July 1, 2001; 131(7): 1965 - 1972. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
F. Mariotti, M. E Pueyo, D. Tomé, S. Bérot, R. Benamouzig, and S. Mahé The Influence of the Albumin Fraction on the Bioavailability and Postprandial Utilization of Pea Protein Given Selectively to Humans J. Nutr., June 1, 2001; 131(6): 1706 - 1713. [Abstract] [Full Text]
|
|
|
|
|
|
F. Mariotti, S. Mahe, C. Luengo, R. Benamouzig, and D. Tome Postprandial modulation of dietary and whole-body nitrogen utilization by carbohydrates in humans Am. J. Clinical Nutrition, October 1, 2000; 72(4): 954 - 962. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C. Morens, C. Gaudichon, C. C. Metges, G. Fromentin, A. Baglieri, P. C. Even, J.-F. Huneau, and D. Tomé A High-Protein Meal Exceeds Anabolic and Catabolic Capacities in Rats Adapted to a Normal Protein Diet J. Nutr., September 1, 2000; 130(9): 2312 - 2321. [Abstract] [Full Text]
|
|
|
|
|
|
C. C. Metges Contribution of Microbial Amino Acids to Amino Acid Homeostasis of the Host J. Nutr., July 1, 2000; 130(7): 1857S - 1864. [Abstract] [Full Text]
|
|
|
|
|
|
D. Tomé and C. Bos Dietary Protein and Nitrogen Utilization J. Nutr., July 1, 2000; 130(7): 1868S - 1873. [Abstract] [Full Text]
|
|
|
|
 |
|
 C. Bos, C. Gaudichon, and D. Tome Nutritional and Physiological Criteria in the Assessment of Milk Protein Quality for Humans J. Am. Coll. Nutr., April 1, 2000; 19(90002): 191S - 205. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
F. Mariotti, S. Mahé, R. Benamouzig, C. Luengo, S. Daré, C. Gaudichon, and D. Tomé Nutritional Value of [15N]-Soy Protein Isolate Assessed from Ileal Digestibility and Postprandial Protein Utilization in Humans J. Nutr., November 1, 1999; 129(11): 1992 - 1997. [Abstract] [Full Text]
|
|
| |||||||||||||
