Insulin and glucose sucrose or starch1 Judith and
Hallfrisch,2 Sheldon
M.S.,
Reiser,5
Frances
responses Lazar,3
B.S.,
in rats fed
Carol
Jorgensen,4
for
1 1 to 13 weeks
M.S.,
Ph.D. Rats
ABSTRACT followed
by
triglyceride
6 to levels
fed
54% sucrose
8 weeks
of
than
fed
rats
meal
feeding
had
comparable
significantly
amounts
of starch
ad libitum higher after
12 to
serum insulin response measured before, #{189}, and 4 hr after a meal showed fed rats to be higher than comparable levels of rats fed starch at all three glucose tolerance test measuring serum glucose before, /2, 1, and 2 hr revealed glucose levels of rats fed sucrose to be higher than levels of rats was added to the injection medium, serum glucose of rats fed sucrose comparable in higher levels.
levels of rats fed starch indicating insulin and triglyceride levels than These
results
tolerance.
Sucrose
feeding
has
been
clear
are
Am.
J. Clin.
evidence
Nutr.
reported
that
32: 787-793,
to cause
elevated serum levels of insulin and triglyceride in humans (1, 2) and in rats (3, 4). Reports of its effect on glucose tolerance are contradictory. Anderson et at. (5) reported that diets containing up to 80% of the calories as sucrose improved glucose tolerance in humans while Cohen et at. (6) have found impairment ofglucose tolerance in humans consuming sucrose in comparison to bread. Other
researchers have little humans
have found sucrose or no effect on glucose (7, 8). Sucrose
feeding
feeding tolerance has
to in
been
re-
ported to decrease insulin sensitivity (9), impair glucose tolerance (10, 1 1), and increase fat deposition in rats (12). Hyperinsulinism, hypertriglyceridemia, glucose intolerance
insulin resistance, have all been linked either heart disease ( 13-15) or diabetes 17), both major health problems in this try.
Meal
feeding
has been
reported
and with (16, coun-
to cause
same effects produced by sucrose feeding in humans such as elevated insulin levels (18) and hypertriglyceridemia (19). Al-
though meal feeding appears to increase insulin sensitivity (20) and improve glucose tolerance
feeding
insulin
The
insensitivity. fed ad libitum
sucrose
feeding
insulin, 14 hr without
ad libitum glucose,
and
food.
The
insulin levels of sucrosetimes. An intraperitoneal after a glucose injection fed starch. When insulin remained higher than
Meal feeding generally resulted but had little effect on glucose
has
undesirable
effects
on
glucose
1979.
toward meal feeding in industrialized ties (23) possible synergistic effects feeding along with meal feeding
socieof sucrose should be
investigated.
Although there are considerable data documenting undesirable effects of sucrose, a clear association between the present level of sucrose consumption in this country and diabetes or heart disease is not generally accepted (24). This study was done to investigate the effects ofsucrose on some parameters associated with these diseases: insulin response, insulin insensitivity, serum levels of insulin, glucose and triglyceride. Meal feeding was used to see if it augmented the effects of sucrose.
Materials
and methods
Ninety-six male weanling Wistar rats were fed a diet containing either 54% sucrose or cooked corn starch and 10% each of lactalbumin and casein, 4% each of beef
of the
some
when
insulin in rats
or S weeks
serum
(11) in the rat, other effects of meal rats such as increases in serum (21) and fat deposition (22) occur also in
rats are
American
fed sucrose. In view of the trend
Journal
of Clinical
Nutrition
32: APRIL
I From the Carbohydrate Nutrition Laboratory, Nutrition Institute, Science and Education Administration, United States Department of Agriculture, Beltsville, Maryland 20705, and the Department of Chemistry, University of Maryland, College Park, Maryland 20740. 2 Biological Laboratory Technician, Carbohydrate Nutrition Laboratory. a Biological Aid, Carbohydrate Nutrition Laboratory. Nutritionist, Department of Chemistry. r, Research Chemist, Carbohydrate Nutri-
tion Laboratory.
1979,
Downloaded from https://academic.oup.com/ajcn/article-abstract/32/4/787/4666390 by University of Glasgow user on 30 June 2018
pp.
787-793.
Printed
in U.S.A.
787
HALLFRISCH
788 TABLE
Meal
I tolerance
ET
AL.
test’ Insulin
Diet/feeding
pattern
Body
wt
Percent
food
consumed
Before
response
meal I/2hr
S
Starch/meal Sucrose/meal
31 1 ± 5.7” 318 ± 4.1”
92.4
Starch/ad libitum Sucrose/ad libitum 2 x 2 ANOVA’
352 367
77.1
Insulin
a
libitum feeding. that do not share effect significant;
± 2.40 ± 0.87 ± 3.26
36 ± 3.6” 45 ± 4.Oh 23 ± l.8e
87.3 ± 2.60
36 ± 5.3”
96.5
5.8c ± 6.8c P ±
NS
of rats
5 weeks
fed
0.75
g of sucrose
of ad libitum
P, feeding
pattern
or starch
effect
significant
mix.’
The
rats
were
kept
in individual
stainless steel cages with wire mesh bottoms in a temperature-humidity controlled room with 12 hr periods of light and dark. The dark cycle was from 8:00 AM to 8:00 PM and the light cycle from 8:00 PM to 8:00 AM. After 5 weeks of ad libitum feeding, 24 rats consuming each diet were meal-fed their respective diets an to 8 weeks for 3 hr during each dark cycle. was done at this time because rats normally portion of their food (approximately 80%)
The light cycle was reversed during
additional 6 Meal feeding eat the major
regular
work
was drawn
after and 4 hr. 1 1 to 13 weeks of feeding, from all rats at the end of a regular to 14 hr without food, blood samples After
and
triglyceride
food was removed 3-hr meal. After 12 were analyses.
collected Eight
for rats
from each of the four diet/treatment groups received ip injections with 250 mg glucose per 100 g body weight in Krebs-Ringer bicarbonate buffer, pH 7.4. Eight rats from each
of the 6
Vitamin
(gram/kilogram
four diet
groups
received
fortification
mix):
para
ip injections mixture
aminobenzoic
samples
were
obtained
after
samples
were collected
with
(Teklad)
acid,
the
contains
11.013;
ascorbic acid, 101.66; biotin, 0.044; vitamin B12 (0.1% trituration in mannitol), 2.974; calcium pantothenate, 6.608; choline chloride dihydrogen citrate, 349.692; folic acid, 0.198; inositol, 1 1.013; menadione, 4.956; niacin, 9.912; pyridoxine . HCI, 2.203; riboflavin, 2.203; thiamin.
HCI, 2.203; retinyl palmitate concentrate (500,000 IU/ g), 3.96; ergocalciferol (500,000 IU/g), 0.441; tocopheryl acetate (500 IU/g), 24.229. (Mention of a trademark or proprietary product does not constitute a guarantee or warranty ofthe product by the United States Department of Agriculture, and does not imply its approval to the exclusion of other products that may also be suitable.)
Downloaded from https://academic.oup.com/ajcn/article-abstract/32/4/787/4666390 by University of Glasgow user on 30 June 2018
from
was nicked with a scalpel, tamed by gently stroking. adequate for the entire meal
tolerance
test. Bleeding
removed Serum
for 12 to 14 hr. Blood samples for insulin were taken from the tail. The rats were meal tolerance test which consisted of feeding them 0.75 g of diet per 100 g body weight. Food cups were removed and weighed after 15 mm, and blood
above + 0.25 IU final 32 rats (eight
with the glucose 1.0 IU of insulin per 100 g body weight. collected at #{189}, 1, and 2 hr after injection.
day.
feeding pattern determinations then given a
glucose,
±
35 ± 77 ± l0.0’ D,P
injections
in alcohol and applying by stroking. Epididymal
for convenience the
received
described weight. The
at night (26). so that meal
Two weeks before the termination of the experiment after a total of 9 to 10 weeks of feeding, food was removed from 12 rats consuming each diet from each
insulin,
3.6k 8W 4.8b
±
(P < 0.05).
group)
occur
29 52
feeding
tamin
would
13.1”
g body
glucose medium per 100 g body
time
±
155 ± 23.0 81 ± 7.? 94 ± 18.2h D,P
D,P diet/l00
tallow, lard, corn oil, hydrogenated coconut oil, and cellulose, 5% Bernhart-Tomarelli salt mix (25), and vifortification
1 14
serum
weight after 12 to 14 hr without food at followed by 4 to 5 weeks of meal feeding or 9 to 10 weeks of ad Results expressed as mean ± SEM of 1 1 to 12 determinations. “‘ Only values within a column the same superscript(s) are significantly different (P < 0.05). C NS, no significant effects; D, diet
response
the end of either
4hr
Lunh1s insulin/mi
decapitation.
of insulin from
each
medium BlOOd
The
All other
+
was 2-hr blood
the tail. The end of the tail and blood flow was mainUsually, one cut each was tolerance and for the glucose
was stopped direct pressure, and perirenal
by dipping the tail and was restarted fat
pads
were
and weighed was analyzed
immediately after decapitation. for glucose essentially by the (27), insulin by the double antibody
hexokinase method method of Hales and Randle (28), and triglyceride by a modification of the method of Eggstein (29). The data were subjected to analyses of variance (ANOVA) and Duncan’s multiple range test (30). Differences of P < 0.05 are reported as statistically significant.
Results
Table 1 shows body weights at the time of the meal tolerance, percentage of food consumed in 15 min, and serum insulin levels before, #{189}, and 4 hr after the meal (0.75 g of diet per 100 g body weight). Body weights of the ad libitum-fed rats were significantly greater than of meal-fed rats, but there was no diet effect. Although meal-fed rats ate a greater percentage ofthe diet than ad libitumfed rats, there were no statistical differences in food consumed. At all sampling times, before, #{189}, and 4 hr, there were significant diet and feeding pattern effects on serum insulin levels. All group means for sucrose-fed rats were higher than for corresponding starchfed rats, but not all differences were significant. The most notable effect was at 4 hr after the meal, when insulin levels in rats fed su-
INSULIN
crose
were
about
twice
starch. levels
Before and of meal-fed
higher
than
AND
as high
GLUCOSE
as in rats
RESPONSES
insulin
levels
of ad
libitum-fed
levels
789
RATS
no significant differences, but glucose levels of rats fed starch reached a minimum at 1 hr while levels of the rats fed sucrose continued to decline from 1 hr to 2 hr after injection.
fed
#{189} hr after the meal, insulin rats were significantly
rats, but 4 hr after the meal insulin ad libitum-fed rats were higher. Table 2 shows data for glucose
IN
The
of
pattern
of glucose
response
to 0.25 IU of
than corresponding levels of rats fed starch, indicating an impaired response to both en-
insulin was essentially the same as the response to 1.0 IU of insulin. The decline of glucose levels after injection indicates that the insulin was effective. The 2-hr insulin levels of rats fed sucrose and receiving injections with insulin were significantly higher than levels of rats fed starch. The rats mealfed starch had the lowest 2-hr insulin levels. Table 3 shows body and adipose tissue weights, and combined serum levels of insutin, glucose, and triglyceride after 12 to 14 hr without food. For all parameters measured
dogenous
the
tests
of
tolerance glucose medium medium + 1.0 IU of insulin weight. Serum insulin levels
rats
injected
with
and with glucose per 100 g body at 2 hr after injection effect ofdiet on serum
are also shown. The glucose was significant
in most cases; however, feeding little effect. With two exceptions cose levels of rats fed sucrose
fed
and
exogenous
sucrose.
levels
The
was
insulin
effect
significant
pattern had serum gluwere higher
at
in the
of diet
on
#{189} and
2 hr
rats
glucose
than were
ad libitum-fed of rats fed
levels of rats not statistically
levels
of rats
rats. sucrose
with
1 .0 IU
Diet/feeding
glucose
tolerance
Although are higher
of insulin
Glucose Before
was
mg/WI.)
weighi
0
134
±
9.1
Sucrose/meal
0
136
±
10.5
244
Starch/ad libitum Sucrose/adlibitum
0 0
114 ± 146 ±
11.1
202
8.5
223
1.0 1.0 1.0
139 151 128
±
8.2
±
7.0’
±
6.5”
91
±
8.9”
1.0
159
±
l0.3
140
±
22.8’
libitum
2X2ANOVK’ ii
Serum
without either
Results
154
NS
2X2ANOVAd
Sucrose/adlibitum
7.8” ± 35.8e ± l3.5b ± 17.2’
glucose
expressed
same superscript(s) feeding pattern
the
and
insulin
are effect
±
SEM
significantly significant,
(.
D ‘
91
triglyceride
levels
this
of rats levels
Insulin
of
levels
4.8k
98 ±
±
65
l3.Ov
102 ± 77 ± 98 ±
of 6 to 8 determinations. different (P < 0.05). D x P, diet
x pattern
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uinhis/ml
‘
155 169 122
±
163
±
± ±
injection or starch of meal
after feeding
46
±
77h
9. 1’
49
±
14.2h 12.5
30 40
±
4.2’ 4.8h
±
35h
P
100
±
16.4
105
±
79
±
12.3 16.5 1 1.6
209 177 203
±
74 ± 75 ± NS
of 250 mg glucose 12 to 14 hr without or 1 1 to 13 weeks
serum
5.2’
D 13.Oh 20.3’ 13.7h 8W
D
to intraperitoneal
of rats fed sucrose by 6 to 8 weeks
2hr
2hr
DxP
±
D
responses
addition of insulin for 5 weeks followed
as mean
than
and
mt serum
145 ± 5.2” 200 ± 25.7’ 187 ± 21.?’ 171 ± 8.0’
±
D
or with ad libitum
during
higher
hr
Starch/meal
Starch/meal Sucrose/meal Starch/ad
recorded
response
l/2hr
g body
not
feeding different.
injection
j
IU/IbVJ
although a
test”
I. nsuinin-
pattern
significant,
means within always statistically
per 100 g body weight were significantly higher in rats fed the sucrose diet before, #{189},were significantly fed starch. Insulin and 1 hr after injection. At 2 hr there were TABLE 2 Intraperitoneal
was
study, but a preliminary experiment has shown that meal-fed rats eat about 80 to 85% of the amount consumed by ad libitum-fed rats. A previous study indicates that rats more readily consume the sucrose diet than the starch diet ( 12). Ad libitum-fed rats were significantly heavier and fatter than meal-fed rats. Serum glucose levels of rats fed sucrose
fed starch, the differences significant. The glucose
injected
of diet
treatment were not
pattern Food intake
in rats
receiving injections with glucose only. The insulin levels at 2 hr after injection of glucose alone were significantly higher in meal-fed rats than in insulin levels
effect
specific
24.? 43.2’ ± 19.5h ± 12.3’ D
per
100 g body
weight
food. The rats were fed of ad libitum feeding.
b. C Only values within a column that do not share NS, no significant effects; D, diet effect significant;
interaction
significant
(P < 0.05).
the P.
790
HALLFRISCH
TABLE 3 Body and fat weights Diet/feeding
.
and serum
ET
AL.
profiled .
pattern
Final
Starch/meal
body
Epididymal
WI
2x2ANOVA’
perirenal
g
gil00
g body
± 89h ± 7.2’ 374 ± 6.5” 402 ± 7.8e D,P
3.2 4.7 4.0 5.1
± O.2O ± 0.19” ± 0.19’
300 344
Sucrose/meal Starch/ad libitum Sucrose/ad libitum
+
±
at
0.26”
Serum
insulin
.
Serum
glucose
unhIs/m!
mg/100
136 ± 4.?
34 ± 34h 46 ± 6.0’ 23 ± 3.2”
33
D,P
±
mt
165
16’ 18’ 96 ± 1?
C
144 ± 6.0’ 122 ± 5.6” 150 ± 5.1’ D
3.2’
D,P
.
triglycende
Serum
±
185 ±
171 ± 20’ D,P
weight and serum profile of rats fed sucrose or starch either ad libitum for 5 weeks followed by 6 to 8 of meal feeding or ad libitum feedinfor 1 1 to 13 weeks after 12 to 14 hr without food. Results expressed as mean ± SEM of 20 to 24 determinations. C Only values within a column that do not share the same superscript(s) are significant (P < 0.05). “ D. diet effect significant; P, feeding pattern effect significant (P < 0.05). a
Body
weeks
meal-fed
rats
libitum-fed
were
rats.
affected
higher
Feeding
than
levels
pattern
all parameters
except
of ad
significantly
glucose
level.
Discussion
An abnormal insulin response with a normat glucose tolerance is considered to be the earliest detectable symptom associated with diabetes (3 1). The meal tolerance test was used to determine the insulin response of rats that were adapted to a semisynthetic diet containing 54% carbohydrate as either sucrose
or starch.
The
meal
tolerance
has
sev-
eral advantages over a glucose tolerance test. The insulin response is measured under normal dietary conditions and includes the effects of other diet components, such tein (32) and fat, on the total response. cose is not a usual dietary component could affect gastrointestinal hormones
enzymes starch.
differently The
meal
than
tolerance
the also
as proGluand and
sucrose would
or
include
the effects on the insulin response of dietary adaptations such as increased sucrose activity in sucrose-fed rats. Since sucrose is one-half fructose which is not insulinogenic, one might expect the insulin response to be lower with sucrose
than
with
starch
which
is comprised
entirely ofglucose. However, Curry et at. (33) found fructose, in the presence of glucose, to be insulinogenic. In the meal tolerance test the greatest percent difference in insulin levels between rats fed sucrose and starch was at 4 hr after the meal. At this time insulin levels of rats fed sucrose
are
about
two
times
their
before
meal
values. The delay in the return of insulin levels to normal is a sign of glucose intolerance (3 1). According to Trout et al. (34)
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sucrose
leaves
the stomach
more
quickly
than
starch. Evidence also indicates that the digestion and absorption of sucrose are faster in sucrose-fed rats than in starch-fed rats (3). The components of a sucrose diet, therefore, would appear in the blood more quickly than components of a starch diet. The elevated 4hr levels of insulin in sucrose-fed rats cannot be explained on the basis of intestinal differences, such as differences in transport or in enzyme activity, but appear to represent an adaptive decrease in sensitivity to insulin. There is evidence that the arterial wall is an insulin-sensitive tissue and that chronic exposure to high insulin levels results in the development of the type oflipid-filled lesions that are found in early atherosclerosis (14). The ratio of insulin to glucose is significantly higher in diabetics with atherosclerosis than in diabetics without atherosclerosis (35). Two observations indicate that an elevated insulin level might be the cause oflater abnormalities of carbohydrate and lipid metabolism found in patients with atherosclerotic disease: 1) carbohydrate intolerant subjects respond to oral glucose with hyperinsulinemia (36) and 2) insulin levels in diabetic patients with atherosclerosis are higher in than in diabetics without atherosclerosis (37). Olefsky et at. (15)
postulated
that
insulin
resistance
is the
primary step that leads to hyperinsulinemia and then to hypertriglyceridemia. Hypertriglyceridemia is considered an important risk factor in heart disease (38). In our study sucrose
feeding
caused
increases
in both
rum levels of insulin and triglyceride. In contrast to a previously reported (12),
insulin
meal tolerance the meal than
levels
of meal-fed
rats
were generally higher levels of ad libitum-fed
se-
study during
before rats.
a
INSULIN
One
possible
is that
explanation
in the
pr,evious
AND
GLUCOSE
for this discrepancy study
the
meal-fed
rats
were much less fat than rats fed ad libitum. They began to meal feed at weaning and ate much less than the ad libitum-fed rats. Apparently most of their food was converted to energy rather than stored as fat. High insulin values were, therefore, not required physiologically. Our data agree with those of Wiley and Leveille (21), who found higher “fasting” levels of insulin in meal-fed rats than in ad libitum-fed rats. In the Wiley and Leveille (21) study comparable
the weights to weights
of meal-fed rats of ad libitum-fed
were rats.
In our study, 4 hr after the meal, the insulin levels of rats fed ad libitum had not returned to levels found before the meal. This indication of glucose intolerance could be due partially to their increased body fat. It is possible that 12 to 14 hr without food did not have equal physiological effects on meal-fed and ad libitum-fed groups. It may take longer for levels of meal-fed rats to return to pre-meal levels than for ad libitum-fed rats. Unpublished results indicate that stomach contents after 12 to 14 hr without food are greater in meal-fed differences
than in
in ad libitum-fed physiological
rats. These status of the
meal-fed and ad libitum-fed rats may contribute to the differences in fasting insulin and triglyceride in rats on the different feeding patterns. The ip glucose tolerance test measures the response
ofadapted
rats
to the same
stimulus.
It allows direct measurement of the effects of endogenous insulin and endogenous + exogenous insulin. Rezek (39) feels that the two act differently, but in our study sucrose-fed rats appear to be less sensitive to both types of insulin than rats fed starch. Sucrose-fed rats almost always had higher glucose levels than starch-fed rats, which is an indication of insulin resistance especially in view of their higher insulin levels. An inverse relationship was reported between serum insulin and the number of effective insulin receptors (40). The higher the serum insulin levels are, the lower is the number of effective receptor sites. Insulin levels measured 2 hr after injection do not reflect the same pattern as the insulin values 4 hr after the meal tolerance. In the ip test the insulin levels of meal-fed rats are higher at 2 hr than levels of ad libitum-fed rats, while in the meal tolerance test the
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RESPONSES
791
IN RATS
insulin levels ofad libitum-fed rats are higher at 4 hr. Many factors could contribute to this difference. The meal tolerance test was given orally and gastrointestinal hormones and other intestinal factors could influence the level of insulin or glucose. The response to the ip tolerance test would be expected to be faster than the response to the meal tolerance since the ip test bypasses the digestive tract. Glucose received
levels of the starch meal-fed rats that injections with 1 IU of insulin at 1 hr and rebounded at 2 hr, mdi-
dipped cating that glucose levels dropped so low that other factors controlling glucose homeostasis, possibly glucagon, growth hormone, and cortisol, intervened to restore glucose to normal levels. Serum glucose of starch-fed rats that received
injections
with
glucose
only
de-
creased more rapidly than glucose levels of comparable sucrose-fed rats, indicating a greater sensitivity to insulin. The extremely high levels ofglucose at #{189} hr in these sucrosefed and starch ad libitum-fed rats (all > 200) are an indication of glucose intolerance. In the ad libitum-fed rats this could be due to increased fat deposition. Hypertriglyceridemia,
independent
of any
elevation of cholesterol, is considered to be a risk factor for atherosclerosis (41). Farquhar et a!. (42) found that the increase in triglyceride levels in response to high carbohydrate ingestion is proportional to the postprandial increase in insulin produced by the diets. In our study a 2 x 2 ANOVA showed that triglyceride levels were significantly higher in sucrose-fed rats than in starch-fed rats. Olefsky
et at. (43)
reported
that
fasting
ide is a major determinant triglyceride response. They correlations
levels ships
and were
between
insulin independent
crose-fed
rats
bly
starch,
fed
plasma
response.
were
triglyceride
Both
relation-
of obesity.
fatter the
triglycer-
of postprandial also found high
than
question
Since
rats
su-
compara-
arises
as
to
whether sucrose produces metabolic changes indirectly by promoting increased body fat or by a direct effect on the insulin secreting mechanism. Therefore, correlation coefficients (data not shown) between total removable fat (epididymal and perirenal) and affected metabolic parameters were determined. The correlation between triglyceride level and removable fat was significant only in the starch meal-fed rats. The correlation
792
HALLFRISCH
between in both starch-fed relations
The
insulin
and
body
fat was significant
groups of sucrose-fed rats, but not in rats. There were no significant corbetween body fat and blood glucose.
correlations
insulin, glucose, not due solely although there the sucrose-fed levels.
indicate
ET
that
increases
15.
in the
16.
and triglyceride levels are to increased fat deposition, may be some connection in rats between fat and insulin
17.
a
References P. J., K. F. CARROLL AND N. HAVENSTEIN. Plasma triglyceride response to carbohydrates, fats, and caloric intake. Metabolism 19: 1, 1970. 2. NAISMITH, D. J., A. L. STOCK AND J. YUDKIN. Effect of changes in the proportions of the dietary carbohydrates and in energy intake on the plasma lipid concentrations in healthy young men. Nutr. Metabol. 16: 295, 1974. 3. REISER, S., 0. MICHAELIS, IV, J. PUTNEY AND J. HALLFRISCH. Effect of sucrose feeding on the intestinal transport of sugars in two strains of rats. J. Nutr. 105: 894, 1975. 4. LAUBE, H., H. U. KL#{246}R,R. FUSSGANGER AND E. F. PFEIFFER. The effect of starch, sucrose, glucose, and fructose on lipid metabolism in rats. Nutr. Metabol. 15: 273, 1973. 5. ANDERSON, J. W., R. H. HERMAN AND D. ZAKIM. NESTEL,
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12.
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and
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F. T.
Interaction
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heart
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23.
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WADHWA,
K. L., AND G. A. LEVEILLE. Metabolic adaptations in meal-fed rats; effects of increased meal frequency or ad libitum feeding in rats previously adapted to a single daily meal. J. Nutr. 100: 450, 1970. FABRY, P., AND J. TEPPERMAN. Meal frequency-a possible factor in human pathology. Am. J. Clin. Nutr. 23: 1059, 1970. Scoos,-69. Evaluation of the health aspects of sucrose as a food ingredient, Contract No. FDA 22375-2004. Bethesda, Md.: Life Sciences Research Of1976.
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cagon, and the cyclic nucleotide protein kinase tem in rats. J. Nutr. 107: 746, 1977. BONDAR, R. J. L., AND D. MEAD. Evaluation
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EGGSTIEN,
and glycerol In: Methods Bergmeyer. 1825-1841.
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30. relationship
triglyceridemia. Am. J. Med. 57: 55 1, 1974. H. P., AND A. M. GLASGOW. Juvenile diabetes mellitus and serum lipids and lipoprotein levels. Am. J. Diseases Children 130: 1 1 13, 1976. COHEN, A. M. High sucrose intake as a factor in the development of diabetes and its vascular complications. Hearings Before the Select Committee on Nutrition and Human Needs of the United States SenCHASE,
22. MUIRURI,
on
glucose tolerance in normal men. Am. J. Clin. Nutr. 26: 600, 1973. COHEN, A. M., A. TEITELBAUM, M. BALOGH AND J. J. GROEN. Effect of interchanging bread and sucrose as main source of carbohydrate in a low fat diet on the glucose tolerance curve of healthy volunteer subjects. Am. J. Clin. Nutr. 19: 59, 1966. FRY, A. J. The effect of a “sucrose-free” diet on oral glucose tolerance in man. Nutr. Metabol. 14: 313, 1972. BRUNZELL, J. D., R. L. LERNER, D. PORTE, JR. AND E. L. BIERMAN. Effect ofa fat free, high carbohydrate diet on diabetic subjects with fasting hyperglycemia. Diabetes 23: 138, 1974. VRANA, A., Z. SLABOCHOVA, L. KAZDOVA AND P. FABRY. Insulin sensitivity of adipose tissue and serum insulin concentration in rats fed sucrose or starch diets. Nutr. Rept. Internat. 3: 31, 1971. COHEN, A. M., AND A. TEITELBAUM. Effect of dietary sucrose and starch on oral glucose tolerance and insulin-like activity. Am. J. Physiol. 206: 105, 1964. RoMsos, D. R., AND G. A. LEVEILLE. Effect of meal frequency and diet composition on glucose tolerance in the rat. J. Nutr. 104: 1503, 1974. REISER, S., AND J. HALLFRISCH. Insulin sensitivity and adipose tissue weight of rats fed starch or sucrose diets ad libitum or in meals. J. Nutr. 107: 147, 1977.
lating insulin levels to atherosclerosis. Atherosclerosis 27: 1, 1977. OLEFSKY, J. M., J. W. FARQUHAR AND 0. M. REAVEN. Reappraisal of the role of insulin in hyper-
P. 5., E. A. YOUNG, K. SCHMIDT, C. E. ELSON AND D. J. PRINGLE. Metabolic consequences of feeding frequency in man. Am. J. Clin. Nutr. 26: 823, 1973. 19. GWINUP, 0., R. C. BYRON, W. H. R0USH, F. A. KRUGER AND G. J. HAMWI. Effect ofnibbling versus gorging on serum lipids in man. Am. J. Clin. Nutr. 13: 209, 1963. 20. BRAUN, T., A. VRANA AND P. FABRY. Enhanced hypoglycemic effect of exogenous insulin associated with an increased response of adipose tissue and a diminished response in the diaphragm in “meal-fed” rats. Experientia 23: 468, 1967. 21. WILEY, J. H., AND G. A. LEVEILLE. Significance of insulin in the metabolic adaptation of rats to meal ingestion. J. Nutr. 100: 1073, 1970. 18.
1.
AL.
SNEDECOR,
M., AND E. determination of Enzymatic New York:
Triglycerides after alkaline hydrolysis. Analysis, edited by H. U. Academic Press, 1974, p.
KUHLMANN.
G. W., AND W. 0. COCHRAN.
of all differences
between
pairs
of means.
Inspection In: Statis-
INSULIN
AND
GLUCOSE
tical Press,
31. 32.
Methods. Ames, Iowa: Iowa State University 1967, p. 27 1-275. KRAFT, J. R., AND R. A. NOSAL. Insulin values and diagnosis of diabetes. Lancet I: 637, 1975. TURNER, M. R., AND J. S. BRYANT. Insulin secretion in young and adult offspring of rats given diets of
RESPONSES
varying 33.
protein
and
nancy and lactation. CURRY, D. L., K.
tose potentiation 91: 34.
35.
1493,
sucrose
content
during
preg-
Proc. Nutr. Soc. 35: 123A, P. CURRY AND M. GOMEZ.
of insulin
secretion.
Endocrinology
40.
1972. D. L.,
Atherosclerosis
in
diabetes
mellitus.
Arch.
41.
Insulin
and
non-esterified
fatty
acid
me-
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M. The
REZEK,
role
of insulin
in the
glucostatic
control of food intake. Can. J. Physiol. Pharmacol. 54: 650, 1976. MAUGH, T. H., II. Hormone receptors-new clues to the cause of diabetes. Science 193: 220, 1976. CARLSON, L. A., AND L. E. B#{246}I-rIGER. lschaemic heart disease in relation to fasting values of plasma
and cholesterol. Lancet I: 865, 1972. J. W., A. FRANK, R. C. GROSS AND 0.
FARQUHAR,
M. REAVEN.
Med.
HOFFMAN.
tabolism in asymptomatic diabetes and atherosclerotic subjects. Canad. Med. Assoc. J. 102: 1 165, 1970. ALBRINK, M. J., AND E. B. MAN. Serum triglycerides in coronary heart disease. Arch. Internal Med. 103:
triglyceride 42.
Internal
130: 833, 1972. 36. BERSON, S. A., AND R. S. YALOW. Some current controversies in diabetes research. Diabetes 14: 549, 1965. 37. KASHYAP, L., F. MAGILL, L. Roins AND M. M.
793
RATS
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1976. Fruc-
E. S. CONWAY AND J. D. PUTNEY. Dietary influences on gastric emptying of carbohydrate versus fat in the rat. J. Nutr. 107: 104, 1977. SANTEN, R. J.,P. W. WILLIS, Ill AND S. S. FAJANS. TROUT,
38.
IN
Glucose, insulin and triglyceride reand low carbohydrate diets in man. J. Clin. Invest. 45: 1648, 1966. OLEFSKY, J. M., P. CRAPO AND 0. M. REAVEN. Postprandial plasma triglyceride and cholesterol response
43.
sponses 1976.
to high
to a low-fat
meal.
Am. J. Clin.
Nutr.
29: 535,
Hallfrisch,2 Sheldon
M.S.,
Reiser,5
Frances
responses Lazar,3
B.S.,
in rats fed
Carol
Jorgensen,4
for
1 1 to 13 weeks
M.S.,
Ph.D. Rats
ABSTRACT followed
by
triglyceride
6 to levels
fed
54% sucrose
8 weeks
of
than
fed
rats
meal
feeding
had
comparable
significantly
amounts
of starch
ad libitum higher after
12 to
serum insulin response measured before, #{189}, and 4 hr after a meal showed fed rats to be higher than comparable levels of rats fed starch at all three glucose tolerance test measuring serum glucose before, /2, 1, and 2 hr revealed glucose levels of rats fed sucrose to be higher than levels of rats was added to the injection medium, serum glucose of rats fed sucrose comparable in higher levels.
levels of rats fed starch indicating insulin and triglyceride levels than These
results
tolerance.
Sucrose
feeding
has
been
clear
are
Am.
J. Clin.
evidence
Nutr.
reported
that
32: 787-793,
to cause
elevated serum levels of insulin and triglyceride in humans (1, 2) and in rats (3, 4). Reports of its effect on glucose tolerance are contradictory. Anderson et at. (5) reported that diets containing up to 80% of the calories as sucrose improved glucose tolerance in humans while Cohen et at. (6) have found impairment ofglucose tolerance in humans consuming sucrose in comparison to bread. Other
researchers have little humans
have found sucrose or no effect on glucose (7, 8). Sucrose
feeding
feeding tolerance has
to in
been
re-
ported to decrease insulin sensitivity (9), impair glucose tolerance (10, 1 1), and increase fat deposition in rats (12). Hyperinsulinism, hypertriglyceridemia, glucose intolerance
insulin resistance, have all been linked either heart disease ( 13-15) or diabetes 17), both major health problems in this try.
Meal
feeding
has been
reported
and with (16, coun-
to cause
same effects produced by sucrose feeding in humans such as elevated insulin levels (18) and hypertriglyceridemia (19). Al-
though meal feeding appears to increase insulin sensitivity (20) and improve glucose tolerance
feeding
insulin
The
insensitivity. fed ad libitum
sucrose
feeding
insulin, 14 hr without
ad libitum glucose,
and
food.
The
insulin levels of sucrosetimes. An intraperitoneal after a glucose injection fed starch. When insulin remained higher than
Meal feeding generally resulted but had little effect on glucose
has
undesirable
effects
on
glucose
1979.
toward meal feeding in industrialized ties (23) possible synergistic effects feeding along with meal feeding
socieof sucrose should be
investigated.
Although there are considerable data documenting undesirable effects of sucrose, a clear association between the present level of sucrose consumption in this country and diabetes or heart disease is not generally accepted (24). This study was done to investigate the effects ofsucrose on some parameters associated with these diseases: insulin response, insulin insensitivity, serum levels of insulin, glucose and triglyceride. Meal feeding was used to see if it augmented the effects of sucrose.
Materials
and methods
Ninety-six male weanling Wistar rats were fed a diet containing either 54% sucrose or cooked corn starch and 10% each of lactalbumin and casein, 4% each of beef
of the
some
when
insulin in rats
or S weeks
serum
(11) in the rat, other effects of meal rats such as increases in serum (21) and fat deposition (22) occur also in
rats are
American
fed sucrose. In view of the trend
Journal
of Clinical
Nutrition
32: APRIL
I From the Carbohydrate Nutrition Laboratory, Nutrition Institute, Science and Education Administration, United States Department of Agriculture, Beltsville, Maryland 20705, and the Department of Chemistry, University of Maryland, College Park, Maryland 20740. 2 Biological Laboratory Technician, Carbohydrate Nutrition Laboratory. a Biological Aid, Carbohydrate Nutrition Laboratory. Nutritionist, Department of Chemistry. r, Research Chemist, Carbohydrate Nutri-
tion Laboratory.
1979,
Downloaded from https://academic.oup.com/ajcn/article-abstract/32/4/787/4666390 by University of Glasgow user on 30 June 2018
pp.
787-793.
Printed
in U.S.A.
787
HALLFRISCH
788 TABLE
Meal
I tolerance
ET
AL.
test’ Insulin
Diet/feeding
pattern
Body
wt
Percent
food
consumed
Before
response
meal I/2hr
S
Starch/meal Sucrose/meal
31 1 ± 5.7” 318 ± 4.1”
92.4
Starch/ad libitum Sucrose/ad libitum 2 x 2 ANOVA’
352 367
77.1
Insulin
a
libitum feeding. that do not share effect significant;
± 2.40 ± 0.87 ± 3.26
36 ± 3.6” 45 ± 4.Oh 23 ± l.8e
87.3 ± 2.60
36 ± 5.3”
96.5
5.8c ± 6.8c P ±
NS
of rats
5 weeks
fed
0.75
g of sucrose
of ad libitum
P, feeding
pattern
or starch
effect
significant
mix.’
The
rats
were
kept
in individual
stainless steel cages with wire mesh bottoms in a temperature-humidity controlled room with 12 hr periods of light and dark. The dark cycle was from 8:00 AM to 8:00 PM and the light cycle from 8:00 PM to 8:00 AM. After 5 weeks of ad libitum feeding, 24 rats consuming each diet were meal-fed their respective diets an to 8 weeks for 3 hr during each dark cycle. was done at this time because rats normally portion of their food (approximately 80%)
The light cycle was reversed during
additional 6 Meal feeding eat the major
regular
work
was drawn
after and 4 hr. 1 1 to 13 weeks of feeding, from all rats at the end of a regular to 14 hr without food, blood samples After
and
triglyceride
food was removed 3-hr meal. After 12 were analyses.
collected Eight
for rats
from each of the four diet/treatment groups received ip injections with 250 mg glucose per 100 g body weight in Krebs-Ringer bicarbonate buffer, pH 7.4. Eight rats from each
of the 6
Vitamin
(gram/kilogram
four diet
groups
received
fortification
mix):
para
ip injections mixture
aminobenzoic
samples
were
obtained
after
samples
were collected
with
(Teklad)
acid,
the
contains
11.013;
ascorbic acid, 101.66; biotin, 0.044; vitamin B12 (0.1% trituration in mannitol), 2.974; calcium pantothenate, 6.608; choline chloride dihydrogen citrate, 349.692; folic acid, 0.198; inositol, 1 1.013; menadione, 4.956; niacin, 9.912; pyridoxine . HCI, 2.203; riboflavin, 2.203; thiamin.
HCI, 2.203; retinyl palmitate concentrate (500,000 IU/ g), 3.96; ergocalciferol (500,000 IU/g), 0.441; tocopheryl acetate (500 IU/g), 24.229. (Mention of a trademark or proprietary product does not constitute a guarantee or warranty ofthe product by the United States Department of Agriculture, and does not imply its approval to the exclusion of other products that may also be suitable.)
Downloaded from https://academic.oup.com/ajcn/article-abstract/32/4/787/4666390 by University of Glasgow user on 30 June 2018
from
was nicked with a scalpel, tamed by gently stroking. adequate for the entire meal
tolerance
test. Bleeding
removed Serum
for 12 to 14 hr. Blood samples for insulin were taken from the tail. The rats were meal tolerance test which consisted of feeding them 0.75 g of diet per 100 g body weight. Food cups were removed and weighed after 15 mm, and blood
above + 0.25 IU final 32 rats (eight
with the glucose 1.0 IU of insulin per 100 g body weight. collected at #{189}, 1, and 2 hr after injection.
day.
feeding pattern determinations then given a
glucose,
±
35 ± 77 ± l0.0’ D,P
injections
in alcohol and applying by stroking. Epididymal
for convenience the
received
described weight. The
at night (26). so that meal
Two weeks before the termination of the experiment after a total of 9 to 10 weeks of feeding, food was removed from 12 rats consuming each diet from each
insulin,
3.6k 8W 4.8b
±
(P < 0.05).
group)
occur
29 52
feeding
tamin
would
13.1”
g body
glucose medium per 100 g body
time
±
155 ± 23.0 81 ± 7.? 94 ± 18.2h D,P
D,P diet/l00
tallow, lard, corn oil, hydrogenated coconut oil, and cellulose, 5% Bernhart-Tomarelli salt mix (25), and vifortification
1 14
serum
weight after 12 to 14 hr without food at followed by 4 to 5 weeks of meal feeding or 9 to 10 weeks of ad Results expressed as mean ± SEM of 1 1 to 12 determinations. “‘ Only values within a column the same superscript(s) are significantly different (P < 0.05). C NS, no significant effects; D, diet
response
the end of either
4hr
Lunh1s insulin/mi
decapitation.
of insulin from
each
medium BlOOd
The
All other
+
was 2-hr blood
the tail. The end of the tail and blood flow was mainUsually, one cut each was tolerance and for the glucose
was stopped direct pressure, and perirenal
by dipping the tail and was restarted fat
pads
were
and weighed was analyzed
immediately after decapitation. for glucose essentially by the (27), insulin by the double antibody
hexokinase method method of Hales and Randle (28), and triglyceride by a modification of the method of Eggstein (29). The data were subjected to analyses of variance (ANOVA) and Duncan’s multiple range test (30). Differences of P < 0.05 are reported as statistically significant.
Results
Table 1 shows body weights at the time of the meal tolerance, percentage of food consumed in 15 min, and serum insulin levels before, #{189}, and 4 hr after the meal (0.75 g of diet per 100 g body weight). Body weights of the ad libitum-fed rats were significantly greater than of meal-fed rats, but there was no diet effect. Although meal-fed rats ate a greater percentage ofthe diet than ad libitumfed rats, there were no statistical differences in food consumed. At all sampling times, before, #{189}, and 4 hr, there were significant diet and feeding pattern effects on serum insulin levels. All group means for sucrose-fed rats were higher than for corresponding starchfed rats, but not all differences were significant. The most notable effect was at 4 hr after the meal, when insulin levels in rats fed su-
INSULIN
crose
were
about
twice
starch. levels
Before and of meal-fed
higher
than
AND
as high
GLUCOSE
as in rats
RESPONSES
insulin
levels
of ad
libitum-fed
levels
789
RATS
no significant differences, but glucose levels of rats fed starch reached a minimum at 1 hr while levels of the rats fed sucrose continued to decline from 1 hr to 2 hr after injection.
fed
#{189} hr after the meal, insulin rats were significantly
rats, but 4 hr after the meal insulin ad libitum-fed rats were higher. Table 2 shows data for glucose
IN
The
of
pattern
of glucose
response
to 0.25 IU of
than corresponding levels of rats fed starch, indicating an impaired response to both en-
insulin was essentially the same as the response to 1.0 IU of insulin. The decline of glucose levels after injection indicates that the insulin was effective. The 2-hr insulin levels of rats fed sucrose and receiving injections with insulin were significantly higher than levels of rats fed starch. The rats mealfed starch had the lowest 2-hr insulin levels. Table 3 shows body and adipose tissue weights, and combined serum levels of insutin, glucose, and triglyceride after 12 to 14 hr without food. For all parameters measured
dogenous
the
tests
of
tolerance glucose medium medium + 1.0 IU of insulin weight. Serum insulin levels
rats
injected
with
and with glucose per 100 g body at 2 hr after injection effect ofdiet on serum
are also shown. The glucose was significant
in most cases; however, feeding little effect. With two exceptions cose levels of rats fed sucrose
fed
and
exogenous
sucrose.
levels
The
was
insulin
effect
significant
pattern had serum gluwere higher
at
in the
of diet
on
#{189} and
2 hr
rats
glucose
than were
ad libitum-fed of rats fed
levels of rats not statistically
levels
of rats
rats. sucrose
with
1 .0 IU
Diet/feeding
glucose
tolerance
Although are higher
of insulin
Glucose Before
was
mg/WI.)
weighi
0
134
±
9.1
Sucrose/meal
0
136
±
10.5
244
Starch/ad libitum Sucrose/adlibitum
0 0
114 ± 146 ±
11.1
202
8.5
223
1.0 1.0 1.0
139 151 128
±
8.2
±
7.0’
±
6.5”
91
±
8.9”
1.0
159
±
l0.3
140
±
22.8’
libitum
2X2ANOVK’ ii
Serum
without either
Results
154
NS
2X2ANOVAd
Sucrose/adlibitum
7.8” ± 35.8e ± l3.5b ± 17.2’
glucose
expressed
same superscript(s) feeding pattern
the
and
insulin
are effect
±
SEM
significantly significant,
(.
D ‘
91
triglyceride
levels
this
of rats levels
Insulin
of
levels
4.8k
98 ±
±
65
l3.Ov
102 ± 77 ± 98 ±
of 6 to 8 determinations. different (P < 0.05). D x P, diet
x pattern
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uinhis/ml
‘
155 169 122
±
163
±
± ±
injection or starch of meal
after feeding
46
±
77h
9. 1’
49
±
14.2h 12.5
30 40
±
4.2’ 4.8h
±
35h
P
100
±
16.4
105
±
79
±
12.3 16.5 1 1.6
209 177 203
±
74 ± 75 ± NS
of 250 mg glucose 12 to 14 hr without or 1 1 to 13 weeks
serum
5.2’
D 13.Oh 20.3’ 13.7h 8W
D
to intraperitoneal
of rats fed sucrose by 6 to 8 weeks
2hr
2hr
DxP
±
D
responses
addition of insulin for 5 weeks followed
as mean
than
and
mt serum
145 ± 5.2” 200 ± 25.7’ 187 ± 21.?’ 171 ± 8.0’
±
D
or with ad libitum
during
higher
hr
Starch/meal
Starch/meal Sucrose/meal Starch/ad
recorded
response
l/2hr
g body
not
feeding different.
injection
j
IU/IbVJ
although a
test”
I. nsuinin-
pattern
significant,
means within always statistically
per 100 g body weight were significantly higher in rats fed the sucrose diet before, #{189},were significantly fed starch. Insulin and 1 hr after injection. At 2 hr there were TABLE 2 Intraperitoneal
was
study, but a preliminary experiment has shown that meal-fed rats eat about 80 to 85% of the amount consumed by ad libitum-fed rats. A previous study indicates that rats more readily consume the sucrose diet than the starch diet ( 12). Ad libitum-fed rats were significantly heavier and fatter than meal-fed rats. Serum glucose levels of rats fed sucrose
fed starch, the differences significant. The glucose
injected
of diet
treatment were not
pattern Food intake
in rats
receiving injections with glucose only. The insulin levels at 2 hr after injection of glucose alone were significantly higher in meal-fed rats than in insulin levels
effect
specific
24.? 43.2’ ± 19.5h ± 12.3’ D
per
100 g body
weight
food. The rats were fed of ad libitum feeding.
b. C Only values within a column that do not share NS, no significant effects; D, diet effect significant;
interaction
significant
(P < 0.05).
the P.
790
HALLFRISCH
TABLE 3 Body and fat weights Diet/feeding
.
and serum
ET
AL.
profiled .
pattern
Final
Starch/meal
body
Epididymal
WI
2x2ANOVA’
perirenal
g
gil00
g body
± 89h ± 7.2’ 374 ± 6.5” 402 ± 7.8e D,P
3.2 4.7 4.0 5.1
± O.2O ± 0.19” ± 0.19’
300 344
Sucrose/meal Starch/ad libitum Sucrose/ad libitum
+
±
at
0.26”
Serum
insulin
.
Serum
glucose
unhIs/m!
mg/100
136 ± 4.?
34 ± 34h 46 ± 6.0’ 23 ± 3.2”
33
D,P
±
mt
165
16’ 18’ 96 ± 1?
C
144 ± 6.0’ 122 ± 5.6” 150 ± 5.1’ D
3.2’
D,P
.
triglycende
Serum
±
185 ±
171 ± 20’ D,P
weight and serum profile of rats fed sucrose or starch either ad libitum for 5 weeks followed by 6 to 8 of meal feeding or ad libitum feedinfor 1 1 to 13 weeks after 12 to 14 hr without food. Results expressed as mean ± SEM of 20 to 24 determinations. C Only values within a column that do not share the same superscript(s) are significant (P < 0.05). “ D. diet effect significant; P, feeding pattern effect significant (P < 0.05). a
Body
weeks
meal-fed
rats
libitum-fed
were
rats.
affected
higher
Feeding
than
levels
pattern
all parameters
except
of ad
significantly
glucose
level.
Discussion
An abnormal insulin response with a normat glucose tolerance is considered to be the earliest detectable symptom associated with diabetes (3 1). The meal tolerance test was used to determine the insulin response of rats that were adapted to a semisynthetic diet containing 54% carbohydrate as either sucrose
or starch.
The
meal
tolerance
has
sev-
eral advantages over a glucose tolerance test. The insulin response is measured under normal dietary conditions and includes the effects of other diet components, such tein (32) and fat, on the total response. cose is not a usual dietary component could affect gastrointestinal hormones
enzymes starch.
differently The
meal
than
tolerance
the also
as proGluand and
sucrose would
or
include
the effects on the insulin response of dietary adaptations such as increased sucrose activity in sucrose-fed rats. Since sucrose is one-half fructose which is not insulinogenic, one might expect the insulin response to be lower with sucrose
than
with
starch
which
is comprised
entirely ofglucose. However, Curry et at. (33) found fructose, in the presence of glucose, to be insulinogenic. In the meal tolerance test the greatest percent difference in insulin levels between rats fed sucrose and starch was at 4 hr after the meal. At this time insulin levels of rats fed sucrose
are
about
two
times
their
before
meal
values. The delay in the return of insulin levels to normal is a sign of glucose intolerance (3 1). According to Trout et al. (34)
Downloaded from https://academic.oup.com/ajcn/article-abstract/32/4/787/4666390 by University of Glasgow user on 30 June 2018
sucrose
leaves
the stomach
more
quickly
than
starch. Evidence also indicates that the digestion and absorption of sucrose are faster in sucrose-fed rats than in starch-fed rats (3). The components of a sucrose diet, therefore, would appear in the blood more quickly than components of a starch diet. The elevated 4hr levels of insulin in sucrose-fed rats cannot be explained on the basis of intestinal differences, such as differences in transport or in enzyme activity, but appear to represent an adaptive decrease in sensitivity to insulin. There is evidence that the arterial wall is an insulin-sensitive tissue and that chronic exposure to high insulin levels results in the development of the type oflipid-filled lesions that are found in early atherosclerosis (14). The ratio of insulin to glucose is significantly higher in diabetics with atherosclerosis than in diabetics without atherosclerosis (35). Two observations indicate that an elevated insulin level might be the cause oflater abnormalities of carbohydrate and lipid metabolism found in patients with atherosclerotic disease: 1) carbohydrate intolerant subjects respond to oral glucose with hyperinsulinemia (36) and 2) insulin levels in diabetic patients with atherosclerosis are higher in than in diabetics without atherosclerosis (37). Olefsky et at. (15)
postulated
that
insulin
resistance
is the
primary step that leads to hyperinsulinemia and then to hypertriglyceridemia. Hypertriglyceridemia is considered an important risk factor in heart disease (38). In our study sucrose
feeding
caused
increases
in both
rum levels of insulin and triglyceride. In contrast to a previously reported (12),
insulin
meal tolerance the meal than
levels
of meal-fed
rats
were generally higher levels of ad libitum-fed
se-
study during
before rats.
a
INSULIN
One
possible
is that
explanation
in the
pr,evious
AND
GLUCOSE
for this discrepancy study
the
meal-fed
rats
were much less fat than rats fed ad libitum. They began to meal feed at weaning and ate much less than the ad libitum-fed rats. Apparently most of their food was converted to energy rather than stored as fat. High insulin values were, therefore, not required physiologically. Our data agree with those of Wiley and Leveille (21), who found higher “fasting” levels of insulin in meal-fed rats than in ad libitum-fed rats. In the Wiley and Leveille (21) study comparable
the weights to weights
of meal-fed rats of ad libitum-fed
were rats.
In our study, 4 hr after the meal, the insulin levels of rats fed ad libitum had not returned to levels found before the meal. This indication of glucose intolerance could be due partially to their increased body fat. It is possible that 12 to 14 hr without food did not have equal physiological effects on meal-fed and ad libitum-fed groups. It may take longer for levels of meal-fed rats to return to pre-meal levels than for ad libitum-fed rats. Unpublished results indicate that stomach contents after 12 to 14 hr without food are greater in meal-fed differences
than in
in ad libitum-fed physiological
rats. These status of the
meal-fed and ad libitum-fed rats may contribute to the differences in fasting insulin and triglyceride in rats on the different feeding patterns. The ip glucose tolerance test measures the response
ofadapted
rats
to the same
stimulus.
It allows direct measurement of the effects of endogenous insulin and endogenous + exogenous insulin. Rezek (39) feels that the two act differently, but in our study sucrose-fed rats appear to be less sensitive to both types of insulin than rats fed starch. Sucrose-fed rats almost always had higher glucose levels than starch-fed rats, which is an indication of insulin resistance especially in view of their higher insulin levels. An inverse relationship was reported between serum insulin and the number of effective insulin receptors (40). The higher the serum insulin levels are, the lower is the number of effective receptor sites. Insulin levels measured 2 hr after injection do not reflect the same pattern as the insulin values 4 hr after the meal tolerance. In the ip test the insulin levels of meal-fed rats are higher at 2 hr than levels of ad libitum-fed rats, while in the meal tolerance test the
Downloaded from https://academic.oup.com/ajcn/article-abstract/32/4/787/4666390 by University of Glasgow user on 30 June 2018
RESPONSES
791
IN RATS
insulin levels ofad libitum-fed rats are higher at 4 hr. Many factors could contribute to this difference. The meal tolerance test was given orally and gastrointestinal hormones and other intestinal factors could influence the level of insulin or glucose. The response to the ip tolerance test would be expected to be faster than the response to the meal tolerance since the ip test bypasses the digestive tract. Glucose received
levels of the starch meal-fed rats that injections with 1 IU of insulin at 1 hr and rebounded at 2 hr, mdi-
dipped cating that glucose levels dropped so low that other factors controlling glucose homeostasis, possibly glucagon, growth hormone, and cortisol, intervened to restore glucose to normal levels. Serum glucose of starch-fed rats that received
injections
with
glucose
only
de-
creased more rapidly than glucose levels of comparable sucrose-fed rats, indicating a greater sensitivity to insulin. The extremely high levels ofglucose at #{189} hr in these sucrosefed and starch ad libitum-fed rats (all > 200) are an indication of glucose intolerance. In the ad libitum-fed rats this could be due to increased fat deposition. Hypertriglyceridemia,
independent
of any
elevation of cholesterol, is considered to be a risk factor for atherosclerosis (41). Farquhar et a!. (42) found that the increase in triglyceride levels in response to high carbohydrate ingestion is proportional to the postprandial increase in insulin produced by the diets. In our study a 2 x 2 ANOVA showed that triglyceride levels were significantly higher in sucrose-fed rats than in starch-fed rats. Olefsky
et at. (43)
reported
that
fasting
ide is a major determinant triglyceride response. They correlations
levels ships
and were
between
insulin independent
crose-fed
rats
bly
starch,
fed
plasma
response.
were
triglyceride
Both
relation-
of obesity.
fatter the
triglycer-
of postprandial also found high
than
question
Since
rats
su-
compara-
arises
as
to
whether sucrose produces metabolic changes indirectly by promoting increased body fat or by a direct effect on the insulin secreting mechanism. Therefore, correlation coefficients (data not shown) between total removable fat (epididymal and perirenal) and affected metabolic parameters were determined. The correlation between triglyceride level and removable fat was significant only in the starch meal-fed rats. The correlation
792
HALLFRISCH
between in both starch-fed relations
The
insulin
and
body
fat was significant
groups of sucrose-fed rats, but not in rats. There were no significant corbetween body fat and blood glucose.
correlations
insulin, glucose, not due solely although there the sucrose-fed levels.
indicate
ET
that
increases
15.
in the
16.
and triglyceride levels are to increased fat deposition, may be some connection in rats between fat and insulin
17.
a
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