Metabolic
Response
to Egg White and Cottage Frank 0.
Cheese
Protein
in Normal
Subjects
Nuttall and Mary C. Gannon
In type II diabetic subjects, we previously demonstrated differences in the serum insulin, C-peptide, and glucagon response to ingestion of seven different protein sources when administered with 50 g of glucose. The response was smallest with egg white and greatest with cottage cheese protein. In the present study, we compared the responses to 50 g of the above two proteins ingested without glucose in normal male subjects. We also determined the proportion of each ingested protein converted to urea nitrogen. The incremental area response integrated over 8 hours for serum insulin, C-peptide, glucagon, a-amino-nitrogen (AAN), and urea nitrogen were all approximately 50% less following egg white. This was associated with a 50% smaller conversion of protein to urea. Overall, 70% of the cottage cheese but only 47% of the egg white protein could be accounted for by urea formation. Most likely the smaller hormonal response to egg white is due to poor digestibility of this protein. @ 1990 by W.B. Saunders Company.
I
N PREVIOUS
STUDIES,’ we determined that ingested beef protein is just as potent on a weight basis as ingested glucose in stimulating insulin secretion in type II diabetic subjects. In addition, beef protein ingested with glucose resulted in a synergistic effect on the post-meal insulin increase. Subsequently, in type II diabetic subjects, we determined the serum glucose, insulin, glucagon, a-amino-nitrogen (AAN) (total amino acids), and urea nitrogen responses to 50 g of glucose ingested with 25 g of protein in the form of seven different dietary protein sources in order to determine if these various proteins produced differing metabolic responses.’ In general, the responses were similar for these various proteins. However, the smallest insulin stimulatory effect was observed after egg white protein and the greatest after cottage cheese protein. The AAN and glucagon responses also were considerably less with egg white when compared with cottage cheese. This was somewhat surprising since egg white protein generally is considered to be a readily digestible and high-quality protein. In order to further characterize possible differences in the metabolic response to these two proteins, we administered 50 g of each in a random sequence to normal subjects without glucose or other foods. We were particularly interested in possible differences in the insulin and glucagon stimulatory effects and in the increase in AAN and the rate of metabolism to urea of these two proteins in normal persons. Differences in these and other parameters to the two proteins were clearly present. The studies were performed for 8 hours, since it has been reported that protein digestion is relatively slow.’
drawn before and at 30 minutes,
1, 2. 3. 4. 5, 6. 7, and 8 hours after
ingestion of the meals. Water
was given as the control
given as 50-g portions amount
of cottage
meal (-480
of either cottage
mL).
Protein
was
cheese or egg white. The
cheese given was 294 g, grade
A, dry, and not
more than 0.5% milk fat, from Old Home, Minneapolis,
MN, and
was served with salt, pepper, and an herb packet. The egg white (460 g raw weight)
was beaten slightly.
drops of yellow food coloring scrambled
and cooked in a microwave.
eggs. The meals were served with 2 cups (-480
decaffeinated
coffee.
Six
were added. to give the appearance
During
the subsequent
g-hour
of
mL) of
period,
the
subjects were allowed to consume water ad libitum. Plasma glucose was determined a Beckman
glucose
Instruments,
Fullerton,
measured
with
CA).
Serum
by a standard
Health
Science
an
by RIA Center
by Endotech, using
(Dallas
30-K
of Goodwin.’
antibody
RIA methodb with kits produced
reactivity
MN).
C-peptide
The
with proinsulin.
were determined
Serum
KY. Glucagon purchased using has
lyzer (Eastman Kodak, Rochester, NY). The areas above the measured fasting
only
Corp a 4%
fatty acids (NEFA)
assay of Duncombe.’
were determined
from by the
a double-
by Immune-Nuclear
to C-peptide
was
(RIA)
was determined
nonesterified
by the calorimetric
ides and urea nitrogen
Louisville, antiserum
was measured
antibody
(Beckman insulin
radioimmunoassay
TX). AAN
method
(Stillwater.
OL electrode
immunoreactive
double-antibody
method using kits produced was determined
by a glucose oxidase method using
analyzer
Triglycer-
using an EktaChem concentration
ana-
were calcu-
lated using the trapezoid rule, and verified by planimetry. Statistics were performed using Student’s r test for paired variates, using the Statview
512+
program
(Brain
Power, Calabasas.
for the Macintosh computer (Apple Computer, Cupertino, CA). A P value of c.05 was the criterion for significance. Data are presented as the mean t SEM. CA)
MATERIALS AND METHODS Seven normal male subjects were studied in a metabolic unit. All subjects were in excellent health. The mean age was 30 years, with a range of 22 to 38 years. All were within 20% of desirable body weight using the 1959 Metropolitan Life Insurance Co Tables4 All subjects gave written informed consent, and the study was approved by the Medical Center Committee on Human Subjects. All the participants had ingested a diet containing at least 200 g carbohydrate per day with adequate food energy for 3 days before testing. After an overnight fast of 12 hours, an indwelling catheter was inserted into an antecubital vein and kept patent with a small amount of heparin, which was aspirated and discarded before obtaining each sample. Test meals were given at 8:00 AM. Blood was Metabolism, Vol 39, No 7 (July), 1990: pp 749-755
From the Metabolic Research Laboratory and the Section of Endocrinology. Metabolism, and Nutrition, VA Medical Center: and the Departments of Medicine, and Food Science and Nutrition, University of Minnesota, Minneapolis, MN. Supported by Merit Review Research Funds from the Veterans Administration, andfunds from the National Dairy Board, administered in cooperation with the National Dairy Council. Address reprint requests to Frank Q. Nuttall. MD, PhD. Chief, Section of Endocrinology, Metabolism, and Nutrition (1 I IG), VA Medical Cenier, Minneapolis, MN 55417. @ 1990 by W.B. Saunders Company. 00260495/90/3907-0015$03.00/0
749
NUTTALL AND GANNON
750
RESULTS
starving. Ingestion of egg white resulted in little change from the initial fasting value, but it also remained modestly higher than the values present when the subjects were starving (Fig 1C). The insulin incremental area response integrated over 8 hours was approximately twice as great after cottage cheese as after egg white (Fig 1D). When these curves were integrated over 4 hours, the difference was even greater (51 pIJ - h/mL u 21 PU - h/mL or approximately 2.4-fold). The C-peptide curves were similar to the insulin curves (Fig 2A). However, relative to the values when the subjects were starving, the insulin remained modestly elevated after 5 hours, whereas the C-peptide did not. The 8-hour integrated area response was 2.6-fold greater after cottage cheese than after egg white ingestion (Fig 2B). When integrated over 4 hours. the results were similar (2.1 -fold). The AAN concentration decreased modestly over the first hour of starvation, and then stabilized for the duration of the study (Fig 2C). Thus, the curve resembled that for glucose, insulin, and C-peptide. Ingestion of cottage cheese resulted in
When the subjects were starved (water controls) for 8 hours, the serum glucose concentration decreased by approximately 5 mg/dL over the first hour, and then stabilized at this level (87 mg/dL) for the remainder of the study period. The decrease following egg white was modestly less, and following cottage cheese, it was modestly greater (Fig I A). When the areas were integrated over 8 hours using the concentration during starvation as baseline, they were positive for the egg white meal and negative for the cottage cheese meal. The differences were small and were not statistically significant (Fig 1B). When the subjects were starved, the serum insulin concentration also decreased modestly (Fig IC) and the curve was similar to that of the glucose curve (Fig 1A). Cottage cheese stimulated an increase in insulin concentration that reached a maximum at 60 minutes. It then decreased rapidly and reached a minimum by 4 hours. However, it remained higher at the subsequent time points than when the subjects were A
Effect of Protein
on Glucose
Response
6
Effect of Protein
on Glucose
40 ----w---,
Fasting
+ -e-
Egg White Cottage Cheese
0
; 1
F 60
120
180
240
Minutes
C
300
After
Effect of Protein
360
Egg
480
White
Meal
on tnsuiin
X--X O-O 0-O
420
D
Response
;
2
-0
I
( 60
I
I
120 Minutes
240 After
z. E
Area
600 500
-
E
>-z f
60
400
< 2
2
z
40
300
j
200
I
I 360
Meal
20
lo-
_x_‘--x’..x !
0
700
•~~.(~---.
- x.x__+--x---x-, 0
on Insulin
80
- IdO -50
_,o
Cheese
1
z 2
\
Effect of Protein
Cottage
100
Fasting Egg White Cottope Cheese
c ;
-2.0
-40 -20 -r 0
I.0
-1.0
-20
5
1 2.0
T
20 \ k.
Area
I
-.
Y. 480
- -50 0
n
100 Egg White
Cottage
0
Cheese
Fig 1. (A) Glucose response to protein ingestion. The incremental change in plasma glucose was determined for 8 hours after ingestion of the test meals (n = 7 identical subjects for each meal). The test meals consisted of 50 g protein in the form of egg white or cottage cheese, or 480 mL water (fasting control). The mean fasting glucose concentrations were 82, 88, and 81 mg/dL before the water, egg white, and cottage cheese meals, respectively. (8) Effect of protein ingestion on glucose area. The areas under the curves, above the fasting curve (A) were determined using the trapezoid rule.*’ Ears indicate mean ? SEM. (C) Insulin response to protein ingestion. The incremental change in serum insulin was determined for 8 hours after ingestion of the test meals (n = 7). The fasting insulin concentrations were 21. 18. and 18 aU/mL before the water, egg white, and cottage cheese meals, respectively. (D) Effect of protein ingestion on insulin area. The areas above the fasting curve (Cl were determined es indicated above. *Indicates statistical significance, P c .05.
METABOLIC
RESPONSE TO INGESTED PROTEINS
A
Effect of Protein on C-Peptide
0.3 c
X --X
0
O-O
0.2
O-O
t/\
-i
\0
E 2
01.
” 1,
0.0
Response
Fasting Egg White Cottage Cheese
\ _X,
0
l\
60
’
’
’
120
’
240 After
’
X --X O-O O-o
’
”
0
60
’
120 Minutes
’
240 After
I
360
Area
I
0.8 t
, 480
Meol
Effect of Protein on Alpha Amino
-I
on C-Peptide
-0
’ ’
Minutes
C
Effect of Protein
---x--bs.q-4
t-0.2’
B
‘Y.
‘X o/O---0 ‘X. .‘X--
-0.1
751
Nitrogen
Response
Fasting Egg White Cottage Cheese
’
’
360
I
Cottoge Cheese
D Effect of Protein on Alpha Amino Nitrogen
Area
- 2.5 _ 2.0 -
1.5
I-
-0.5
480
Meal
Egg White
Egg White
Cot toge Cheese
Fig 2. (A) C-peptide response to protein ingestion. The incremental change in plasma C-peptide was determined for 8 hours after ingestion of the test meals (n = 7). The fasting C-peptide concentrations were 0.4 pmol/mL before the water, egg white, and cottage cheese meals. (6) Effect of protein ingestion on C-peptide area. The areas under the curves (A) were determined using the trapezoid rule. Bars indicate mean + SEM. *Indicates statistical significance, P 5 .06. (C) AAN response to protein ingestion. The incremental change in plasma AAN was determined for 8 hours after ingestion of the test meals (n = 7). The fasting AAN concentrations were 3.9,4.2. and 4.0 mg/dL before the water, egg white, and cottage cheese meals, respectively. (D) Effect of protein ingestion on AAN area. The areas under the curves (C) were determined as indicated above. *Indicates statistical significance, P 5 .05.
a rapid threefold increase, which reached a peak at 60 minut.es. It then slowly decreased to the control level at 7 hours. Following egg white ingestion, the increase was considerably less, the peak was delayed to 2 hours, and even at 8 hours, the AAN had not quite returned to the control mean (Fig 2C). The integrated area response over 8 hours was approximately twofold greater after cottage cheese (Fig 2D). The plasma glucagon in the subjects when starving decreased over 2 hours and then stabilized (Fig 3A). The decrease was approximately 25% from the initial value (299 + 49 pg/mL). Following cottage cheese ingestion, there was a threefold increase, as with the AAN concentration. It also reached a peak at 60 minutes and then slowly declined. After the 6-hour point, it approached but still remained slightly above the value when the subjects were starved. The response to egg protein again was considerably less (Fig 3A). The integrated area response over 8 hours was approximately twofold greater (2.2) with cottage cheese (Fig 3B). The plasma urea nitrogen (PUN) decreased continuously when the subjects were starved. By 8 hours, it had decreased by approximately 21%. Following cottage cheese ingestion,
the PUN was unchanged for 60 minutes, but then increased rapidly, reaching a maximum at 3 hours. It slowly decreased, but remained clearly elevated even at the 8-hour time point (Fig 3C). Following egg white ingestion, the increase was both slower and smaller than when cottage cheese was ingested. It also remained elevated compared with the 8-hour value when the subjects were starved. The integrated area response was approximately twofold greater (1.8) with cottage cheese (Fig 3D). With 8 hours of starvation, the mean triglyceride remained unchanged (Fig 4A). After 2 hours, it increased following cottage cheese ingestion, to a maximum of approximately 20%) of the concentration at time zero. After egg white, the triglyceride did not increase until 4 hours and the increase was less than after cottage cheese ingestion. At 8 hours, it was still modestly elevated. The integrated area responses also were small (Fig 4B). The NEFA concentration increased slowly and progressively when the subjects were starved. This was a mirror image of the PUN concentration change. Both cottage cheese and egg white ingestion resulted in a transient decrease in NEFA concentration (Fig 4C). This correlated
NU-ITALL AND GANNON
752
AEtfd
of Protein on Glucagon Response
400
X--X
B
Etlect of Prolein on Glucagon Area
z
1000
- 400
Fasting
- 300
\ a
,”
100 0
1
- 200 -100
o_o~“-o
‘x-x__
-100 _20()11I 0
+ O-----d -.-.-. .\ _
-x_
1
I
l
,
!
360
After
Fasting
O-O
Egg
Egg Co’toge
D
F Q
\
o-o,
-X
01 /
O\O
-
-x.
-2 -
--X-
l1.
_
O----O_
20 50
0
60
I 120
’
Minutes
1.0
_
0.5
z
0.0
; 4
-0.5
--x ‘\ ‘X---X---X.__
-4”
Effect of Protein on PUN Area
60
2.0
20
Response
to Egg White and Cottage Frank 0.
Cheese
Protein
in Normal
Subjects
Nuttall and Mary C. Gannon
In type II diabetic subjects, we previously demonstrated differences in the serum insulin, C-peptide, and glucagon response to ingestion of seven different protein sources when administered with 50 g of glucose. The response was smallest with egg white and greatest with cottage cheese protein. In the present study, we compared the responses to 50 g of the above two proteins ingested without glucose in normal male subjects. We also determined the proportion of each ingested protein converted to urea nitrogen. The incremental area response integrated over 8 hours for serum insulin, C-peptide, glucagon, a-amino-nitrogen (AAN), and urea nitrogen were all approximately 50% less following egg white. This was associated with a 50% smaller conversion of protein to urea. Overall, 70% of the cottage cheese but only 47% of the egg white protein could be accounted for by urea formation. Most likely the smaller hormonal response to egg white is due to poor digestibility of this protein. @ 1990 by W.B. Saunders Company.
I
N PREVIOUS
STUDIES,’ we determined that ingested beef protein is just as potent on a weight basis as ingested glucose in stimulating insulin secretion in type II diabetic subjects. In addition, beef protein ingested with glucose resulted in a synergistic effect on the post-meal insulin increase. Subsequently, in type II diabetic subjects, we determined the serum glucose, insulin, glucagon, a-amino-nitrogen (AAN) (total amino acids), and urea nitrogen responses to 50 g of glucose ingested with 25 g of protein in the form of seven different dietary protein sources in order to determine if these various proteins produced differing metabolic responses.’ In general, the responses were similar for these various proteins. However, the smallest insulin stimulatory effect was observed after egg white protein and the greatest after cottage cheese protein. The AAN and glucagon responses also were considerably less with egg white when compared with cottage cheese. This was somewhat surprising since egg white protein generally is considered to be a readily digestible and high-quality protein. In order to further characterize possible differences in the metabolic response to these two proteins, we administered 50 g of each in a random sequence to normal subjects without glucose or other foods. We were particularly interested in possible differences in the insulin and glucagon stimulatory effects and in the increase in AAN and the rate of metabolism to urea of these two proteins in normal persons. Differences in these and other parameters to the two proteins were clearly present. The studies were performed for 8 hours, since it has been reported that protein digestion is relatively slow.’
drawn before and at 30 minutes,
1, 2. 3. 4. 5, 6. 7, and 8 hours after
ingestion of the meals. Water
was given as the control
given as 50-g portions amount
of cottage
meal (-480
of either cottage
mL).
Protein
was
cheese or egg white. The
cheese given was 294 g, grade
A, dry, and not
more than 0.5% milk fat, from Old Home, Minneapolis,
MN, and
was served with salt, pepper, and an herb packet. The egg white (460 g raw weight)
was beaten slightly.
drops of yellow food coloring scrambled
and cooked in a microwave.
eggs. The meals were served with 2 cups (-480
decaffeinated
coffee.
Six
were added. to give the appearance
During
the subsequent
g-hour
of
mL) of
period,
the
subjects were allowed to consume water ad libitum. Plasma glucose was determined a Beckman
glucose
Instruments,
Fullerton,
measured
with
CA).
Serum
by a standard
Health
Science
an
by RIA Center
by Endotech, using
(Dallas
30-K
of Goodwin.’
antibody
RIA methodb with kits produced
reactivity
MN).
C-peptide
The
with proinsulin.
were determined
Serum
KY. Glucagon purchased using has
lyzer (Eastman Kodak, Rochester, NY). The areas above the measured fasting
only
Corp a 4%
fatty acids (NEFA)
assay of Duncombe.’
were determined
from by the
a double-
by Immune-Nuclear
to C-peptide
was
(RIA)
was determined
nonesterified
by the calorimetric
ides and urea nitrogen
Louisville, antiserum
was measured
antibody
(Beckman insulin
radioimmunoassay
TX). AAN
method
(Stillwater.
OL electrode
immunoreactive
double-antibody
method using kits produced was determined
by a glucose oxidase method using
analyzer
Triglycer-
using an EktaChem concentration
ana-
were calcu-
lated using the trapezoid rule, and verified by planimetry. Statistics were performed using Student’s r test for paired variates, using the Statview
512+
program
(Brain
Power, Calabasas.
for the Macintosh computer (Apple Computer, Cupertino, CA). A P value of c.05 was the criterion for significance. Data are presented as the mean t SEM. CA)
MATERIALS AND METHODS Seven normal male subjects were studied in a metabolic unit. All subjects were in excellent health. The mean age was 30 years, with a range of 22 to 38 years. All were within 20% of desirable body weight using the 1959 Metropolitan Life Insurance Co Tables4 All subjects gave written informed consent, and the study was approved by the Medical Center Committee on Human Subjects. All the participants had ingested a diet containing at least 200 g carbohydrate per day with adequate food energy for 3 days before testing. After an overnight fast of 12 hours, an indwelling catheter was inserted into an antecubital vein and kept patent with a small amount of heparin, which was aspirated and discarded before obtaining each sample. Test meals were given at 8:00 AM. Blood was Metabolism, Vol 39, No 7 (July), 1990: pp 749-755
From the Metabolic Research Laboratory and the Section of Endocrinology. Metabolism, and Nutrition, VA Medical Center: and the Departments of Medicine, and Food Science and Nutrition, University of Minnesota, Minneapolis, MN. Supported by Merit Review Research Funds from the Veterans Administration, andfunds from the National Dairy Board, administered in cooperation with the National Dairy Council. Address reprint requests to Frank Q. Nuttall. MD, PhD. Chief, Section of Endocrinology, Metabolism, and Nutrition (1 I IG), VA Medical Cenier, Minneapolis, MN 55417. @ 1990 by W.B. Saunders Company. 00260495/90/3907-0015$03.00/0
749
NUTTALL AND GANNON
750
RESULTS
starving. Ingestion of egg white resulted in little change from the initial fasting value, but it also remained modestly higher than the values present when the subjects were starving (Fig 1C). The insulin incremental area response integrated over 8 hours was approximately twice as great after cottage cheese as after egg white (Fig 1D). When these curves were integrated over 4 hours, the difference was even greater (51 pIJ - h/mL u 21 PU - h/mL or approximately 2.4-fold). The C-peptide curves were similar to the insulin curves (Fig 2A). However, relative to the values when the subjects were starving, the insulin remained modestly elevated after 5 hours, whereas the C-peptide did not. The 8-hour integrated area response was 2.6-fold greater after cottage cheese than after egg white ingestion (Fig 2B). When integrated over 4 hours. the results were similar (2.1 -fold). The AAN concentration decreased modestly over the first hour of starvation, and then stabilized for the duration of the study (Fig 2C). Thus, the curve resembled that for glucose, insulin, and C-peptide. Ingestion of cottage cheese resulted in
When the subjects were starved (water controls) for 8 hours, the serum glucose concentration decreased by approximately 5 mg/dL over the first hour, and then stabilized at this level (87 mg/dL) for the remainder of the study period. The decrease following egg white was modestly less, and following cottage cheese, it was modestly greater (Fig I A). When the areas were integrated over 8 hours using the concentration during starvation as baseline, they were positive for the egg white meal and negative for the cottage cheese meal. The differences were small and were not statistically significant (Fig 1B). When the subjects were starved, the serum insulin concentration also decreased modestly (Fig IC) and the curve was similar to that of the glucose curve (Fig 1A). Cottage cheese stimulated an increase in insulin concentration that reached a maximum at 60 minutes. It then decreased rapidly and reached a minimum by 4 hours. However, it remained higher at the subsequent time points than when the subjects were A
Effect of Protein
on Glucose
Response
6
Effect of Protein
on Glucose
40 ----w---,
Fasting
+ -e-
Egg White Cottage Cheese
0
; 1
F 60
120
180
240
Minutes
C
300
After
Effect of Protein
360
Egg
480
White
Meal
on tnsuiin
X--X O-O 0-O
420
D
Response
;
2
-0
I
( 60
I
I
120 Minutes
240 After
z. E
Area
600 500
-
E
>-z f
60
400
< 2
2
z
40
300
j
200
I
I 360
Meal
20
lo-
_x_‘--x’..x !
0
700
•~~.(~---.
- x.x__+--x---x-, 0
on Insulin
80
- IdO -50
_,o
Cheese
1
z 2
\
Effect of Protein
Cottage
100
Fasting Egg White Cottope Cheese
c ;
-2.0
-40 -20 -r 0
I.0
-1.0
-20
5
1 2.0
T
20 \ k.
Area
I
-.
Y. 480
- -50 0
n
100 Egg White
Cottage
0
Cheese
Fig 1. (A) Glucose response to protein ingestion. The incremental change in plasma glucose was determined for 8 hours after ingestion of the test meals (n = 7 identical subjects for each meal). The test meals consisted of 50 g protein in the form of egg white or cottage cheese, or 480 mL water (fasting control). The mean fasting glucose concentrations were 82, 88, and 81 mg/dL before the water, egg white, and cottage cheese meals, respectively. (8) Effect of protein ingestion on glucose area. The areas under the curves, above the fasting curve (A) were determined using the trapezoid rule.*’ Ears indicate mean ? SEM. (C) Insulin response to protein ingestion. The incremental change in serum insulin was determined for 8 hours after ingestion of the test meals (n = 7). The fasting insulin concentrations were 21. 18. and 18 aU/mL before the water, egg white, and cottage cheese meals, respectively. (D) Effect of protein ingestion on insulin area. The areas above the fasting curve (Cl were determined es indicated above. *Indicates statistical significance, P c .05.
METABOLIC
RESPONSE TO INGESTED PROTEINS
A
Effect of Protein on C-Peptide
0.3 c
X --X
0
O-O
0.2
O-O
t/\
-i
\0
E 2
01.
” 1,
0.0
Response
Fasting Egg White Cottage Cheese
\ _X,
0
l\
60
’
’
’
120
’
240 After
’
X --X O-O O-o
’
”
0
60
’
120 Minutes
’
240 After
I
360
Area
I
0.8 t
, 480
Meol
Effect of Protein on Alpha Amino
-I
on C-Peptide
-0
’ ’
Minutes
C
Effect of Protein
---x--bs.q-4
t-0.2’
B
‘Y.
‘X o/O---0 ‘X. .‘X--
-0.1
751
Nitrogen
Response
Fasting Egg White Cottage Cheese
’
’
360
I
Cottoge Cheese
D Effect of Protein on Alpha Amino Nitrogen
Area
- 2.5 _ 2.0 -
1.5
I-
-0.5
480
Meal
Egg White
Egg White
Cot toge Cheese
Fig 2. (A) C-peptide response to protein ingestion. The incremental change in plasma C-peptide was determined for 8 hours after ingestion of the test meals (n = 7). The fasting C-peptide concentrations were 0.4 pmol/mL before the water, egg white, and cottage cheese meals. (6) Effect of protein ingestion on C-peptide area. The areas under the curves (A) were determined using the trapezoid rule. Bars indicate mean + SEM. *Indicates statistical significance, P 5 .06. (C) AAN response to protein ingestion. The incremental change in plasma AAN was determined for 8 hours after ingestion of the test meals (n = 7). The fasting AAN concentrations were 3.9,4.2. and 4.0 mg/dL before the water, egg white, and cottage cheese meals, respectively. (D) Effect of protein ingestion on AAN area. The areas under the curves (C) were determined as indicated above. *Indicates statistical significance, P 5 .05.
a rapid threefold increase, which reached a peak at 60 minut.es. It then slowly decreased to the control level at 7 hours. Following egg white ingestion, the increase was considerably less, the peak was delayed to 2 hours, and even at 8 hours, the AAN had not quite returned to the control mean (Fig 2C). The integrated area response over 8 hours was approximately twofold greater after cottage cheese (Fig 2D). The plasma glucagon in the subjects when starving decreased over 2 hours and then stabilized (Fig 3A). The decrease was approximately 25% from the initial value (299 + 49 pg/mL). Following cottage cheese ingestion, there was a threefold increase, as with the AAN concentration. It also reached a peak at 60 minutes and then slowly declined. After the 6-hour point, it approached but still remained slightly above the value when the subjects were starved. The response to egg protein again was considerably less (Fig 3A). The integrated area response over 8 hours was approximately twofold greater (2.2) with cottage cheese (Fig 3B). The plasma urea nitrogen (PUN) decreased continuously when the subjects were starved. By 8 hours, it had decreased by approximately 21%. Following cottage cheese ingestion,
the PUN was unchanged for 60 minutes, but then increased rapidly, reaching a maximum at 3 hours. It slowly decreased, but remained clearly elevated even at the 8-hour time point (Fig 3C). Following egg white ingestion, the increase was both slower and smaller than when cottage cheese was ingested. It also remained elevated compared with the 8-hour value when the subjects were starved. The integrated area response was approximately twofold greater (1.8) with cottage cheese (Fig 3D). With 8 hours of starvation, the mean triglyceride remained unchanged (Fig 4A). After 2 hours, it increased following cottage cheese ingestion, to a maximum of approximately 20%) of the concentration at time zero. After egg white, the triglyceride did not increase until 4 hours and the increase was less than after cottage cheese ingestion. At 8 hours, it was still modestly elevated. The integrated area responses also were small (Fig 4B). The NEFA concentration increased slowly and progressively when the subjects were starved. This was a mirror image of the PUN concentration change. Both cottage cheese and egg white ingestion resulted in a transient decrease in NEFA concentration (Fig 4C). This correlated
NU-ITALL AND GANNON
752
AEtfd
of Protein on Glucagon Response
400
X--X
B
Etlect of Prolein on Glucagon Area
z
1000
- 400
Fasting
- 300
\ a
,”
100 0
1
- 200 -100
o_o~“-o
‘x-x__
-100 _20()11I 0
+ O-----d -.-.-. .\ _
-x_
1
I
l
,
!
360
After
Fasting
O-O
Egg
Egg Co’toge
D
F Q
\
o-o,
-X
01 /
O\O
-
-x.
-2 -
--X-
l1.
_
O----O_
20 50
0
60
I 120
’
Minutes
1.0
_
0.5
z
0.0
; 4
-0.5
--x ‘\ ‘X---X---X.__
-4”
Effect of Protein on PUN Area
60
2.0
20
