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Particle size of wheat, maize, and oat test meals: Effects on plasma glucose and insulin responses and on the rate of starch digestion in vitro

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When normal volunteers ate isocaloric wheat-based meals, their plasma insulin responses (peak concentration and area under curve) increased stepwise: whole grains less than cracked grains less than coarse flour less than fine flour. Insulin responses were also greater with fine maizemeal than with whole or cracked maize grains but were similar with whole groats, rolled oats, and fine oatmeal. The peak-to-nadir swing of plasma glucose was greater with wheat flour than with cracked or whole grains. In vitro starch hydrolysis by pancreatic amylase was faster with decreasing particle size with all three cereals. Correlation with the in vivo data was imperfect. Oat-based meals evoked smaller glucose and insulin responses than wheat- or maize-based meals. Particle size influences the digestion rate and consequent metabolic effects of wheat and maize but not oats. The increased insulin response to finely ground flour may be relevant to the etiology of diseases associated with hyperinsulinemia and to the management of diabetes.
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Particle size of wheat, maize, and oat test meals: effects on
Am J Gun Nuir 1988;47:675-82. Printed in USA. © 1988 American Society for Clinical Nutrition 675
plasma glucose and insulin responses and on the rate of
starch digestion in vitro13
Kenneth WHeaton, MD; SamuelNMarcus, MD; Pauline M Emmett, BSc; and Cohn H Bolton, PhD
ABSTRACT When normal volunteers ate isocaloric wheat-based meals, their plasma in-
sulin responses (peak concentration and area under curve) increased stepwise: whole grains
<cracked grains <coarse flour <fine flour. Insulin responses were also greater with fine
maizemeal than with whole or cracked maize grains but were similar with whole groats, rolled
oats, and fine oatmeal. The peak-to-nadir swing ofplasma glucose was greater with wheat flour
than with cracked or whole grains. In vitro starch hydrolysis by pancreatic amylase was faster
with decreasing particle size with all three cereals. Correlation with the in vivo data was imper-
fect. Oat-based meals evoked smaller glucose and insulin responses than wheat- or maize-based
meals. Particle size influences the digestion rate and consequent metabolic effects ofwheat and
maize but not oats. The increased insulin response to finely ground flour may be relevant to
the etiology of diseases associated with hyperinsulinemia and to the management of
diabetes. AmfClinNutr l988;47:675-82.
KEY WORDS Particle size, starch digestion, plasma glucose, plasma insulin, wheat,
maize, oats
Introduction
It might reasonably be expected that within the ali-
mentary tract the more intact the structure of a cereal
grain is, the more slowly the starch within will be di-
gested. Larger food particles have a lower surface-to-vol-
ume ratio and this must reduce the access ofenzymes to
the interior ofthe particle as must the presence of intact
cell walls. However, data to support these ideas are
scanty. A meal of raw wheat flakes evoked a lower
plasma glucose peak than one of whole-meal wheaten
bread (1) but this may have been because raw starch is
poorly digested (2, 3). When rice was ground into flour
it evoked more glycemia and insulinemia than did the
whole grains (4). This phenomenon has not been re-
ported with any other cereal nor have comparisons been
made of coarsely ground and finely milled flour. How-
ever, the in vitro studies ofO’Dea et al (5, 6) suggest that
particle size may be important with wheat, oats, and rye
as well as rice.
The present study was designed to test the hypothesis
stated above. A particular aim was to compare coarsely
milled and finely milled wheat flour because bread and
other wheat-flour products have long been staple foods
but finely milled flour is a relatively recent invention
(7, 8).
Subjects and methods
Test foods
The cereal products used for making the four wheat-based
meals, the three maize-based meals, and the three oat-based
meals were derived from the same batches of English wheat
(Triticum vulgare, variety Avalon), mixed imported maize
(Zea mays), and British oats (Avena sativa). They were milled
at the Flour Milling and Baking Research Association (Chor-
leywood, Herts, UK) in October and November, 1984 and
shipped to Bristol where they were stored at 4 #{176}Cuntil the test
meals were prepared early in 1985.
The four grades of wheat were as follows: whole grains,
cracked grains or kibbled wheat in whjch each grain was broken
into six pieces on average, coarsely milled flour, and finely
milled flour. Both flours were whole meal (ie, unsifted). The
difference in particle size between the coarse and fine flour was
considerable as shown by sieving analysis (Table 1). The fine
flour was similar to the whole-meal flour sold for home baking
in Britain. The coarse flour is not commercially available in
IFrom the University Department of Medicine, Bristol Royal In-
firmary, Bristol, UK.
2Supported by a grant from the Bristol and Weston Health Author-
ity(project #454).
3Reprints not available.
Received February 27, 1987.
Accepted for publication June 16, 1987.
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676 HEATON ET AL
TABLE 1
Sieving analysis ofthe flours and fine meals used in this study and, for comparison, a typical coarse Irish whole-wheat flour
Aperture
Percent retained on sic ye ofgiven aperture afte r sequential sieving
Wheat flour,
fine Wheat flour,
coarse Wheat flour,
Irish Maize meal,
fine Oatmeal,
fine
m
2200
1350
1050
710
390
250
140
-
-
-
-4.2
3.8
13.6
16.9
15.6
7.2
12.1
20.1
5.0
7.5
16.8
15.8
6.6
12.5
16.4
5.7
4.0
-
-
-
0.2
6.8’
13.4
21.8
-
-
-
0.2
9.6’
6.8
13.4
Percent not retained
onanysieve 78.4 15.6 22.1 57.8 70.0
*With maize and oats, Sieves ofaperture 425 and 355 m were used; the percentages retained on the 425.tm sieve were 2.8 and 2.2, respectively,
and on the 355-pm sieve were 4.0 and 7.4, respectively.
England but closely resembles the flour traditionally used for
home baking in Ireland and still widely available there.
The three grades ofmaize were whole kernels, cracked grains
(ie, kernels coarsely chopped up into 23 pieces on average), and
flour (fine maize meal). The three grades of oats were whole
groats; steamed, rolled oats (each flake weighing on average 6.7
mg compared with 17.8 mg for an average groat); and flour
(fine oatmeal). For sieving analysis ofthe maize meal and oat-
meal see Table 1.
The test meals were prepared in batches and frozen at -20
‘C. Spare meals were prepared for use in the in vitro digestion
study.
All test meals were designed to contain 50 g carbohydrate
according to tables of food composition (9, 10). Thus, wheat-
based meals contained 76 g wheat product, maize-based meals
68 g maize product, and oat-based 69 g oat product. The four
batches offlour (coarse and fine wheat flour, fine oatmeal, and
fine maize meal) were each made into scones by forming a
dough with water, salt, baking powder and, to aid palatability,
aspartame (Canderel, GD Searle, High Wycombe, UK) and
baking at 230 #{176}Cfor 10-15 mm. Each of the other six grain
products was weighed into individual tin-foil containers, coy-
ered with 300 mL water, and baked at 180 #{176}Cuntil it was judged
to be cooked. The baking time was 4-5 h for whole grains and
2-3 h for cracked grains and rolled oats.
In vivo plasma glucose and insulin responses
Different but overlapping groups of 10 healthy volunteers
(Table 2) ate in random order and at intervals of at least 48 h
TABLE 2
Sex, age, and body mass index (kg/m2) ofthe groups ofvolunteers who
ate the three cereal-based meals
Cereal eaten Subjects
(M/F)
n
Mean age
(range)
y
Body mass index
(mean ±SEM)
Wheat 5/5 24 (21-37) 21.9 ± 0.63
Oats 9/1 24(21-27) 23.0±0.59
Maize 7/3 24 (2 1-40) 22.2 ±0.48
test breakfasts made from wheat (all four grades), maize (three
grades), or oats (three grades). Studies in women were done
during the first week ofthe menstrual cycle. The duration of the
overnight fast was standardized for each subject. Meals were
thawed overnight and warmed to 40-50 #{176}Cbefore being served.
The meals were weighed so that their water content could be
estimated by subtracting the weight ofthe raw ingredients. The
water content of the breakfast was made up to 350 mL with
decaffeinated coffee or weak tea. Meals were served with a
sprinkling ofaspartame, a few drops oflemonjuice, powdered
nutmeg, or powdered cinnamon as desired to increase palat-
ability. All breakfasts commenced at the same time for a given
subject and were consumed steadily under supervision over a
20-mm period. No attempt was made to standardize the rate
or amount ofmastication. Subjects were comfortably seated in
a quiet room throughout the study period.
Samples of venous blood were taken via an indwelling can-
nula during fasting and at 10, 20, 30, 40, 50, 60, 75, 90, 105,
120, 150, and 180 mm from the beginning ofthe meal. Plasma
samples were immediately separated by centrifugation and fro-
zen until analyzed. Insulin was measured by a standard radio-
immunoassay (1 1), all the samples from each subject’s set of
test meals being analyzed together. Blood glucose was mea-
sured on an autoanalyzer (AAI System, Technicon, Basing-
stoke, UK)by the glucose-oxidase method (12). The area under
the plasma glucose and insulin curves was taken as the area
above the zero-time or 10-mm value, whichever was the lower.
This study was approved by the Bristol and Weston District
Ethical Committee.
In vitro rate ofdigestion ofstarch bypancreatic amylase
Portions of food were incubated with pancreatin (dried pig
pancreas) for differing periods of time to generate differing
amounts of the digestion products glucose, maltose, maltotri-
ose, and a-limit dextrins (H Ghafari, unpublished observa-
tions, 1983). In a second incubation with the enzyme a-glucosi-
dase, the maltose and maltotriose were hydrolyzed to glucose
(as was any starch that was solubilized). The glucose generated
in the two incubations was measured and related to the esti-
mated amount ofstarch in the original food to give a figure for
percent digestion ofstarch at each time. In preliminary experi-
ments with soluble potato starch, conditions for the in vitro
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glucose
mM/I
1.0
6.0
5.0
&#{149}0
______fine flow
- - - coarse flour
crackedgrains 120
110
100
mg/dl
90
I0
70
60
PARTICLE SIZE AND STARCH DIGESTION 677
digestion study were established so that there was maximal
yield ofglucose. In these experiments the mean maximal yield
ofglucose was 68.5 mg/lOO mg starch (68.5%).
Portions of thawed test meal were oven dried at 85 #{176}Cto
constant weight to determine moisture content. Additional
portions were then weighed out to contain ‘360 mg dry solids
(that is, ‘-250 mg starch assuming starch content of ‘-70%)
(9). They were not warmed as the meals were before being
eaten. These portions were mixed thoroughly with 5 mL 0.2
mmol/L phosphate buffer pH 6.5 containing 10 mmol/L so-
dium chloride (digest medium). At time zero, 20 mg grade VI
pancreatin (Sigma Chemical Company, Poole, UK) in 5 mL
digest medium was added to a series of tubes containing the
food suspensions, and all but one of the tubes were incubated
at 37 #{176}C.After 5, 10, 15, 20, 30, 40, and 60 mm incubation (in
the case of the oat-based meals, 15, 30, 45, 60, 90, 120, and
180 mm) one tube was placed on ice to stop the digestion and
centrifuged at 3500 X g for 15 mm at 4 #{176}C.The unincubated
tube was kept on ice and used as a blank. Enzyme-free blanks
were used initially but were never found to generate glucose
and were omitted thereafter. The supernatant was decanted
and diluted 1 to 20 with digest medium containing 20 mmol/
L disodium EDTA. One milliliter of this solution was incu-
bated with two units a-glucosidase (Sigma) in 1 mL digest me-
dium at 25 #{176}Cfor 2 h. Glucose produced was measured by the
standard glucose-oxidase method with o-dianisidine (Sigma).
The mean between-assay coefficients of variations were as
follows: fine-wheat flour, 1 1.0%; coarse-wheat flour, 10.5%;
cracked wheat, 13.8%; whole-wheat grains, 34.9%; maize flour,
18. 1%; cracked maize, 24.8%; whole maize, 1 13.8%; oat flour,
1 1.5%; rolled oats, 22.2%; and whole groats, 18.6%. (At each of
the seven times, n= 5 for wheat products and n=6 for all other
products.) The large mean coefficients with whole grains of
wheat and maize are due to the very low extent of digestion
of these whole grains, which were clearly intact despite being
thoroughly cooked.
Statistical methods
One-way analysis of variance and Student’s ttest for paired
values were used to compare individual values for plasma glu-
cose and insulin, the swing or descent of plasma glucose from
peak to nadir, areas under plasma concentration curves, and
glucose released by in vitro digestion.
Results
In vivo plasma glucose and insulin responses
With the wheat-based meals, plasma glucose tended to
rise higher and fall lower after flour than after cracked or
whole grains (Fig 1). Consequently, the mean swing of
plasma glucose (descent from peak to nadir) was signifi-
cantly greater after flour (Table 3). The area under the
glucose curve tended to be higher after the two flours
than after whole or cracked grains (Table 3) but the
differences were not significant.
Plasma insulin rose significantly higher as the particle
size ofwheat decreased (Fig 2). This was reflected in step-
wise increases in the peak plasma concentration and in
the area under the curve (Table 4, Fig 3). The biggest
difference was between coarse and fine flour, the area un-
der the insulin curve being 38% higher after the fine flour
(p =0.0063).
- - 0 10 20 30 O 50 50 15 90 105 120 150 110
Time (mm)
FIG 1.Mean plasma glucose concentration in 10 normal subjects
after four isocaloric whole-wheat meals ofdifferent particle size.
With the maize-based meals there were no differences
in plasma glucose responses. However, plasma insulin
tended to rise more after maize flour than after cracked
grains or whole maize (Fig 4) and the area under the in-
sulin concentration curve was 60% higher after the flour
than after cracked grains and 89% higher than after
whole maize (Table 4).
With the oat-based meals, plasma glucose tended to
rise higher with decreasing particle size but the areas un-
der the glucose concentration curves were not signifi-
cantly different (Table 3). Similarly, insulin values
showed no relation to particle size (Table 4). Indeed, the
peak insulin concentration and area under the curve
were higher after rolled oats than after fine oatmeal flour
although this difference did not reach statistical signifi-
cance.
When the responses to all three oat-based test meals
were combined and compared with the responses to all
the maize-based and wheat-based meals, the rise in
plasma glucose was substantially less with oats (mean
maximum rise for all oat-based meals, 1.6 ± SEM 0.1
mmol/L vs 2.7 ± 0. 1 for maize and 2.6 ±0. 1 for wheat,
both p<0.001 from unpaired ttests). The area under
the glucose curve was substantially lower after the oat-
based meals (55.2 ±6.4 mmol/L mm vs 94.4 ±7.0 with
maize and 95.0 ±6.3 with wheat, p <0.001 from un-
paired ttests). Furthermore, the area under the insulin
curve after oat flour was only 57% of that after maize
flour and 56% of that after fine wheat flour (p <0.05)
although the particle size profile was similar for all three
flours (Table 1). Different groups ofsubjects ate the three
groups of meals but the subjects were similar in age, sex,
and body mass index (except for a preponderance of
males in the oats group) and had similar fasting values
for plasma glucose (Table 3).
In vitro digestion of starch
With all three cereals the rate of starch digestion was
inversely related to particle size. Thus with wheat the or-
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#{163}0
30
-fine flour
---coarse flour
.cracked rains
whole grains
0 1020 30 050 60 75 90 105 120 150 160
Time (mm)
678 HEATON ET AL
TABLE 3
Plasma glucose responses to meals ofwheat, maize, and oats ofdifferent particle sizes (mean ± SEM)
Plasma glucose concentration Area under
concentration
Fasting Peak Nadir Swing curve
mmol/L mmol/L mmol/L mmol/L mmol/L mm
Wheat
Whole grains 3.8 ±0. 15.9 ±0.2 3.3 ±0.2 2.7 ±0.2 80.5 ±9.7
Cracked grains 3.9 ±0. 1 6.2 ±0.2 3.3 ±0.2 2.9 ±0.2 86.3 ±I 7.8
Coarse flour 3.8 ±0.2 6.5 ±0.2 3. 1±0.2 3.4 ± 0.2 108.2 ± 2.85
Fine flour’ 3.9 ±0. 1 6.6 ±0.2 3.2 ± 0. 1 3.4 ±0.3 106.2 ±1 1.5
Significant differences None None None 4 >lt
3> l,2t None
Maize
Wholegrains 4.0 ±0.1 6.7 ± 0.3 3.2 ± 0.1 3.5 ± 0.4 102.6 ± 15.3
Cracked grains 4. 1 ±0. 1 6.4 ±0.2 3.2 ± 0. 1 3.2 ±0.2 8 1 .4 ±10.4
Flour 3.9 ±0. 1 6.5 ±0.2 3.0 ± 0.2 3.4 ± 0.2 99.3 ± 10.0
Significant differences None None None None None
Oats
Whole grains 3.7 ±0. 1 5.0 ±0.2 3.0 ±0.2 2.0 ±0.2 4 1.0 ± 7.9
Rolled oats 3.7 ± 0. 1 5.3 ± 0.2 3. 1 ± 0.2 2.2 ±0.2 52.9 ±7.8
Flour 3.7 ±0. 1 5.7 ±0.3 3. 1 ±0.2 2.6 ±0.4 7 1.6 ±15.0
Significant differences None None None None None
SOne subject’s data excluded because oftechnical problems in assay ofplasma glucose after this meal.
tp= 0.047 using the unpaired ttest.
 p = 0.022 and 0.040, respectively, using the unpaired Itest.
der of digestion rates was whole grains <cracked grains
<coarse flour <fine flour (Fig 5). There were obvious
differences between whole and cracked grains and be-
tween cracked grains and coarse flour and a significant
further increase in digestion rate with fine vs coarse flour.
With maize and oats (Figs 6 and 7) there was also an
inverse relationship between particle size and rate of di-
insulin
mU/I
FIG 2. Mean plasma insulin concentration in 10 normal subjects
afterfourisocaloric whole-wheat mealsofdifferent particle size. (1 mU!
L = 7.175 pmol/L.)
gestion. With maize the difference between whole and
cracked grains was greater than that between cracked
grains and fine maize meal (flour), at least from 20 mm
onwards.
As fine flour all three cereals were digested at a similar
rate; at 30 mm the conversion of starch to simple sugars
was 46% for wheat, 42% for maize, and 41% for oats.
However, as whole grains, oats were digested much faster
than wheat or maize; at 30 mm, the conversion of starch
to sugars was 18% for oats vs 5% for wheat and 3% for
maize (both p<0.005).
Correlation between in vitro and in vivo measurements
Among the wheat-based meals there was a significant
correlation between in vitro digestibility of a meal (cx-
pressed as the mean percent ofstarch converted to sugars
after 30 mm incubation) and the mean rise in plasma
glucose and between in vitro digestibility and the mean
swing of plasma glucose after the same meal (r =0.96
and 0.97, respectively, p <0.05 for both). The correla-
tion was not significant with the area under the glucose
concentration curve, with the peak plasma insulin, or
with the area under the insulin concentration curve.
Small numbers precluded looking for correlations
among the oat-based and maize-based meals.
Discussion
When wheat and maize are milled before cooking,
their contained starch is digested more rapidly in vitro
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insuLin
mU/I mm
3000
2000
1000
0 whole cracked coarse fine
grains grains flour flour
FIG 3. Area under plasma insulin concentration curve (mean
±SEM)after four isocaloric whole-wheat meals. Significant differences
as follows: fine flour >all others, coarse flour >whole grains.
PARTICLE SIZE AND STARCH DIGESTION 679
TABLE 4
Plasma insulin responses to meals ofwheat, maize, and oats ofdifferent particle sizes (mean ± SEM)
Plasma insuli n concentration
Area under curve
Fasting Peak
mUlL (pmol/L) mUlL (pmol/L) mUlL mm (pmol/L mm)
Wheat
Wholegrains 7.2±1.1(52±9) 31.4±2.8(225±20) 1211±165(8689±1184)
Crackedgrains 7.5± 1.6(54± 11) 34.2±3.8(245±27) 1403±267(10067± 1916)
Coarse flour 6.3 ±1.2(45 ± 9) 37.7 ± 3.0(270 ± 22) 1718 ±160(12327 ± 1148)
Fine flour 8.3 ±1.6(60 ±11) 46.9 ±4.3(337 ±31) 2366 ±279(16976 ±2002)
Significant differences None 4 >1, 2, 3’
3>lt 4>1, 2, 3t
3>l
Maize
Wholegrains 9.3 ±1.5 (67 ±1 1) 41.8 ± 5.2 (300 ±37) 1238 ±212(8883 ±1521)
Crackedgrains 6.9± 1.3(50±9) 42.3±5.5(304±39) 1461 ±243(10483± 1744)
Flour 8.0± 1.7(57± 12) 48.7±7.5(349±54) 2341±459(16797±3293)
Significant differences None None 3 >1, 211
Oats
Wholegrains 8.0 ± 1.0(57 ±7) 36.4 ±3.9(261 ±28) 1 1 1 1 ±169(7971 ±1212)
Rolled oats 7.7 ±1.6(55 ±1 1) 41 .4 ±4.8 (297 ±34) 1701 ±2 1 1 (12204 ±1514)
Flour 7.9± 1.6(57± 11) 36.4±5.3(261 ±38) 1323± 182(9492± 1306)
Significant differences None None None
*p<0.001, 0.028, and 0.003, respectively.
t p <0.001 ,0.019, and 0.017, respectively.
p=0.006.
§p= 0.030.
IIp=0.010 and 0.012, respectively.
and evokes a greater plasma insulin response, indicating
that the starch is digested and absorbed more rapidly in
vivo as well as in vitro. Finely milled wheat flour is di-
gested in vitro significantly faster than its coarsely milled
equivalent and evokes a substantially greater insulin re-
sponse.
Cooking conditions were not identical for all grades of
cereal; all test meals were fully cooked in the everyday
sense, but it is possible that some starch remained ungel-
atinized in the scones, which had briefbaking times. This
being so, our data underestimate the increase in digest-
ibility that occurs when wheat and maize are ground into
flour. Freezing the meals may have caused retrograda-
tion ofsome starch. However, the freezing and reheating
were identical for all meals so there should not have been
any major differences in their content ofresistant starch
(13, 14).
Thus, with wheat and maize the findings were much as
predicted. They indicate that grinding these grains into
flour, especially fine flour, affects their digestibility pro-
foundly, but simply breaking them into several small
pieces has little or no effect.
These conclusions are essentially from the insulin re-
sponses. The glucose responses were not significantly
different with the various grades of wheat and maize cx-
cept that there were differences between the wheat-based
meals for the swing of plasma glucose. Thus, it appears
that measurements of plasma glucose are less sensitive
than measurements of plasma insulin in detecting
differences in the digestibility ofstarch (at least in nondi-
abetic subjects); our previous work suggests the same for
the absorption of sugars from sugar-rich meals (1 1). On
the other hand, both studies indicate that differences in
the responses to foods that would otherwise be missed
can be detected if the swing of plasma glucose is calcu-
lated.
The idea that the structural integrity of starchy foods
determines their rate ofdigestion has been foreshadowed
by studies showing that the plasma glucose and insulin
response to rice and corn is less than that to potato (15-
19) because when rice and corn are cooked, they retain
their solidity and presumably their structure more than
does potato. The traditional, coarsely milled wheat and
rye products bulgur and pumpernickel were reported to
evoke less glycemia (in diabetic subjects) than did ordi-
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_______fine flour
cracked grains
. . whole graiiw
60
50
50
40
30
20
10
insulin
mU/I
mg glucose
per 100mg
starch
10
0 5 10 15 20
I #{149}#{149}#{149} whole grains
30 tO 50 60
Time (mm)
Time (miii)
mg glucose
per 100mg
starch
50
&0
30
20
10
0
mg glucose
per 100mg
starch
- - -- - #{149}i_- - - rolled oats
--- -I- -  .:whole grains
0 15 30 5 60 90 120
Time (mm) 180
680 HEATON ET AL
FIG 4. Mean plasma insulin concentration in 10 normal subjects
after three isocaloric maize meals ofdifferent particle size. (1 mU/L
= 7.175 pmol/L.)
nary wheat and rye bread (20), but in these studies the
source of wheat and rye varied. When normal subjects
swallowed rice, maize, or lumps ofpotato without chew-
ing, the glycemic response was greatly reduced (21); un-
chewed potato can even be recovered from the feces (22).
O’Dea et al (4, 5) compared the glucose and insulin re-
sponses ofnormal subjects to batches ofwhite and brown
rice in two forms, as whole grains and milled into flour,
and found increased glycemia and insulinemia with the
milled materials. They also found starch digestion by
FIG 6. In vitro digestion ofstarch in three maize products of differ-
ent particle size. Glucose and the glucose equivalent of maltose and
maltotriose released at seven time points (mean ±SEM ofsix different
estimations). At every time point the three values are significantly
different from each other(p <0.05). (1 mg glucose = 5.551 mol.)
amylase in vitro to be much faster with the ground rice
and there were close correlations between the percent of
starch digested in 30 mm and the peak plasma glucose
and insulin concentrations.
Correlations between in vitro and in vivo measures of
wheat starch digestion could be demonstrated in this
study but there were anomalies. Correlations existed
with indices ofglucose but not ofinsulin response, which
is paradoxical in view ofthe greater sensitivity of insulin
measurements. The difference between coarse and fine
wheat flour was substantial in vivo (with indices of insu-
lin release) but less impressive in vitro. The striking
difference between whole and cracked maize in vitro had
no counterpart at all in vivo. Ofcourse, the in vitro incu-
bation system is a very crude approximation of gastroin-
testinal events. In particular, it involves nothing equiva-
0 5 10 15 20 ( 40 50 60
Time 1mm)
FIG 5. In vitro digestion ofstarch in four whole-wheat products of
different particle size. Glucose and the glucose equivalent of maltose
and maltotriose released at seven time points (mean ±SEM of five
different estimations). With 38 out ofthe 42 possible comparisons the
mean values are significantly different from each other (p <0.05). (1
mgglucose = 5.551 mol.)
FIG 7. In vitro digestion ofstarch in three oats products of different
particle size. Glucose and the glucose equivalent ofmaltose and malto-
triose released at seven time points (mean ±SEM of six different esti-
mations). With 17 ofthe 21 possible comparisons the mean values are
significantly different from each other(p <0.05). (1 mgglucose = 5.551
zmol.)
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PARTICLE SIZE AND STARCH DIGESTION 681
lent to the chewing of food which, with whole grains es-
pecially, must reduce particle size and facilitate access of
digestive enzymes. Also, there is no preliminary peptic
digestion, which may leave some starch (at least in the
unmilled and coarsely milled products) encapsulated
within a protein matrix (23). Finally, gastric emptying is
a determinant ofthe rate ofdigestion in vivo.
The more rapid digestion of rice, wheat, and maize
when they are cracked or milled into flour is presumably
due to the easier access of amylase to starch when the
surface-to-volume ratio offood particles is increased and
cell walls are mechanically disrupted. Loss of histological
integrity has also been invoked to explain why the starch
in beans, peas, and lentils is digested faster in vitro if the
pulses are dry milled before cooking (24). An additional
factor in vivo may be faster gastric emptying ofsmall par-
tides. However, with maize a 23-fold reduction in parti-
dc size that should have led to faster gastric emptying
made no difference to the plasma insulin response.
With oats the in vitro findings were out of line with
the in vivo findings. In vitro digestion rate increased as
particle size decreased but in vivo the plasma glucose and
insulin responses were not significantly different between
the three oat-based meals. This implies that with oats
there is a factor that strongly influences digestion or ab-
sorption in vivo but that was inoperative in the in vitro
system. This factor could be the viscous properties of the
soluble fl-D-glucan that is the main component of dietary
fiber in oats (25). This gummy material might create a
viscous microclimate in the intestinal lumen and so im-
pede the diffusion ofamylase to starch or the diffusion of
glucose and maltose towards the mucosa. These effects
would have been minimized in the in vitro incubation
because this involved constant mechanical shaking.
Another anomaly with oats was that the meals evoked
relatively small glucose and insulin responses compared
with the other two grains although the starch was di-
gested in vitro equally fast; indeed, whole groats were
more digestible than whole wheat and maize. Again, this
can be explained by oats containing an unusually high
proportion of soluble viscous fiber that limits the rate of
digestion or absorption in vivo. Our findings are consis-
tent with those of Jenkins et al (18) who reported the
glycemic index after oat flakes to be only 49 ± 8 com-
pared with 75 ± 10 after wheat flakes and 80 ± 6 after
corn flakes. A caveat is that the starch content ofour oats
meals may not have been identical with that ofour maize
and wheat meals because we used food-table values for
starch and did not measure it directly.
In conclusion, this study demonstrates that wheat and
maize, two ofthe major staple foods ofmankind, are di-
gested faster the more they are reduced in particle size.
Finely milled wheat flour evokes substantially greater in-
sulin responses than coarsely milled flour. Oat products
do not behave in this way, possibly because ofthe differ-
ent physical properties ofoat fiber. Our finding of greater
insulin secretion after finely milled flour raises the possi-
bility that in susceptible genotypes regular consumption
ofsuch flour increases the risk ofdiseases in which hyper-
insulinemia has a possible etiological role, namely, obe-
sity (26), diabetes (27), gallstones (28), and atherosclero-
sis (29). There may also be a practical consequence. Be-
cause the management of diabetes mellitus is aided by
incorporating into the diet slow-release carbohydrates
such as legume seeds (30), it may also be aided by the
replacement of flour with whole or cracked grains or by
the use ofa coarsely milled flour. 13
The in vitro studies were expertly performed by Miss A Moffau, who
also helped with statistical analysis. Plasma glucose and insulin assays
were carried out by the Chemical Pathology Department ofthe Bristol
Royal Infirmary. Dr SCW Hook kindly provided the samples of whole
and milled wheat, maize, and oats and carried out the sieving analyses
at FMBRA, Chorleywood, Herts, UK. Dr C Oettl#{233}helped with the col-
lection of samples.
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... Wholegrain consumption can improve acute postprandial glycaemia compared with refined grains [1] and is associated with reduced risk of developing type 2 diabetes [2,3] and other non-communicable diseases [3]. More specifically, the grain particle size of wholegrain foods can affect acute postprandial glycaemia and insulinaemia [3][4][5][6][7][8][9][10], so it is an important determinant of the health benefits of wholegrain foods. However, grain particles are not uniformly sized, and therefore, a wholegrain food or ingredient could include a wide range of wholegrain particles from very tiny to fully intact grains. ...
... An alternative method grinds the grains between two millstones to produce a coarser flour, commonly referred to as stoneground flour. Few studies have actually measured the metabolic response to different wholegrain flour [3,6,8,9]. Bread made with stoneground or coarse wholegrain flour results in a lower acute postprandial glycaemic response among people with type 2 diabetes compared to bread made with roller-milled wholegrain flour [3,8], but the same effect has not been shown for people with normal glucose tolerance [6,9,11]. However, consumption of foods made from coarse compared with finely milled flours can result in reduced postprandial insulinaemia in both people with diabetes and those with normal glucose tolerance [6,8,9]. ...
... Few studies have actually measured the metabolic response to different wholegrain flour [3,6,8,9]. Bread made with stoneground or coarse wholegrain flour results in a lower acute postprandial glycaemic response among people with type 2 diabetes compared to bread made with roller-milled wholegrain flour [3,8], but the same effect has not been shown for people with normal glucose tolerance [6,9,11]. However, consumption of foods made from coarse compared with finely milled flours can result in reduced postprandial insulinaemia in both people with diabetes and those with normal glucose tolerance [6,8,9]. ...
Article
Full-text available
Wholegrain flour produced by roller-milling is predominantly comprised of fine particles, while stoneground flour tends to have a comparatively smaller proportion of fine particles. Differences in flour particle size distribution can affect postprandial glycaemia in people with type 2 diabetes and postprandial insulinaemia in people with and without type 2 diabetes. No prior studies have investigated the effect of wholegrain flour particle size distribution on glycaemic or insulinaemic response among people with impaired glucose tolerance or risk factors for type 2 diabetes. In a randomised crossover study, we tested the 180-min acute glycaemic and insulinaemic responses to three wholegrain breads differing in flour particle size and milling method: (1) fine roller-milled flour, (2) fine stoneground flour, and (3) coarse stoneground flour. Participants (n = 23) were males and females with risk factors for type 2 diabetes (age 55–75 y, BMI >28 kg/m2, completing less than 150 min moderate to vigorous intensity activity per week). Each test meal provided 50 g available carbohydrate, and test foods were matched for energy and macronutrients. There was no significant difference in blood glucose iAUC (incremental area under the curve) between the coarse stoneground flour bread and the fine stoneground flour bread (mean difference −20.8 (95% CI: −51.5, 10.0) mmol·min/L) and between the coarse stoneground flour bread and the fine roller-milled flour bread (mean difference −23.3 (95% CI: −57.6, 11.0) mmol·min/L). The mean difference in insulin iAUC for fine stoneground flour bread compared with the fine roller-milled flour bread was −6.9% (95% CI: −20.5%, 9.2%) and compared with the coarse stoneground flour bread was 9.9% (95% CI: −2.6%, 23.9%). There was no evidence of an effect of flour particle size on postprandial glycaemia and insulinaemia among older people with risk factors for type 2 diabetes, most of whom were normoglycaemic.
... Whole and refined grain-based foods vary substantially in composition and properties, starting from the botanical source and grain variety and ending in how they are prepared (9). Food form, food matrix and energy density of the final product (7), processing (10), and other physical properties such as particle size (10)(11)(12)(13) all add complexity to the health value of grain-based foods. ...
... Whole and refined grain-based foods vary substantially in composition and properties, starting from the botanical source and grain variety and ending in how they are prepared (9). Food form, food matrix and energy density of the final product (7), processing (10), and other physical properties such as particle size (10)(11)(12)(13) all add complexity to the health value of grain-based foods. ...
... Yet, semolina had the lowest glycemic response (iAUC 0-120 min ) (although only significantly lower than the whole wheat flour), showing that particle size, and not the whole grain property, reduced glycemic response. Previous studies support this finding with an inverse relation between particle size and glycemic response (10,47), although the meal forms in these studies were not always comparable and included dietary components other than the grain. It is also possible that semolina has a more densely packed endosperm (48) and/or other starch structural features (49) that accounted for its lower glycemic response than the whole wheat flour. ...
Article
Background: Epidemiological and some clinical studies support the view that whole grain foods have lower glycemic response compared to refined grain foods. However, from the perspective of food material properties, it is not clear why whole grain cereals containing mostly insoluble and non-viscous dietary fibers (e.g., wheat) would reduce postprandial glycemia. Objectives: We hypothesized that glycemic response for whole grain wheat milled products would not differ from that of refined wheat when potentially confounding variables (wheat source, food form, particle size, viscosity) are matched. Our objective was to study the effect of whole grain versus refined wheat milled products on postprandial glycemia, gastric emptying, and subjective appetite. Design: Using a randomized crossover design, healthy participants (n = 16) consumed six different medium-viscosity porridges made from whole grain or refined wheat milled products, all from the same grain source and mill: whole wheat flour, refined wheat flour, cracked wheat, semolina, reconstituted wheat flour with fine bran, and reconstituted wheat flour with coarse bran. Postprandial glycemia, gastric emptying, and appetitive response were measured using continuous glucose monitors, the 13C-octanoic acid breath test, and visual analog scale (VAS) ratings. Bayes factors were implemented to draw inferences about null effects. Results: Little-to-no differences were observed in glycemic responses, with lower incremental area under the curve (iAUC0-120 min) glycemic response only for semolina (mean difference [MD]: –966 mg min/dL; 95% CI: –1775, –156; P = 0.02) and cracked wheat (MD: –721 mg min/dL; 95% CI: –1426, –16; P = 0.04) compared to whole wheat flour porridge. Bayes factors suggested weak-to-strong evidence for a null effect (i.e., no effect of treatment type) in glycemic response, gastric emptying, and VAS ratings. Conclusions: While whole grain wheat foods provide other health benefits, they did not in their natural composition confer lower postprandial glycemia or gastric emptying compared to their refined wheat counterparts.
... En effet, l'amidon sous sa forme non transformée est lentement dégradé par les amylases salivaires et pancréatiques. Un autre facteur clé, en plus de la structure de l'amidon réside dans la transformation des aliments qui va déterminer l'étendue de la gélatinisation de l'amidon ainsi que l'intégrité de la taille des particules et de la paroi cellulaire végétale [376,377]. Tous les processus mécaniques qui altèrent la surface des granules d'amidon augmentent leur sensibilité aux enzymes digestives [308,349] car ils perdent partiellement ou totalement leur structure cristalline, permettant une plus grande accessibilité aux enzymes sans les obstructions causées par les doubles hélices ou par les complexes amylose-lipides dans les amidons de céréales [349]. ...
... La modulation des glucides dans l'alimentation, comme outil pour améliorer le contrôle glycémique, a intéressé de nombreux auteurs ces dernières décennies avec un focus de plus en plus fort concernant la qualité des glucides, au-delà même de leur quantité. Dans notre étude, nous nous sommes intéressés à la digestibilité de l'amidon, principal composé glucidique des produits céréaliers, guidés par le fait que plusieurs études, comparant les effets physiologiques de produits amylacés, ont montré une corrélation entre la digestibilité in vitro de l'amidon et les réponses glycémiques et insulinémiques postprandiales [377,416,418,462]. Dans leur métaanalyse, Vinoy et al. [439] ont confirmé les effets de la teneur en SDS des produits céréaliers sur la réponse métabolique et ont montré que la consommation de produits riches en SDS était fortement liée à une réponse glycémique plus faible, induite par une cinétique du taux 213 d'apparition du glucose exogène plus lente et que le degré auquel le SDS affectait la réponse d'apparition exogène du glucose différait selon la teneur en SDS du produit alimentaire. ...
Thesis
L’hyperglycémie chronique est impliquée dans le développement de complications associées au DT2 et la variabilité glycémique (VG) apparait comme une composante à part entière de l'homéostasie du glucose. Les mesures hygiéno-diététiques, en première ligne dans la prise en charge du DT2, passent entre autres par une modification de l’alimentation, dans laquelle les glucides occupent une place prépondérante. Au-delà de la quantité, la qualité des glucides a été mise en avant comme ayant un impact déterminant sur les excursions glycémiques. Notamment, la digestibilité des produits à base d’amidon pourrait alors avoir un impact sur le contrôle glycémique chez les patients atteints de DT2. Mais il y a aujourd’hui un réel besoin d’apporter une caractérisation des produits plus complète sur cet aspect et de mener des études de faisabilité et d’efficacité de tels régimes modulant la digestibilité de l’amidon. Mes travaux de thèse montrent qu’il est possible de concevoir un régime riche en amidon lentement digestible (SDS), grâce à des choix de produits amylacés disponibles dans le commerce, des conseils de cuisson et des recommandations adaptées. Pour la première fois, nous avons montré que le contrôle de la digestibilité de l'amidon de produits amylacés avec des instructions de cuisson appropriées dans une population atteinte de DT2 augmentait la consommation de contenu en SDS dans un contexte de vie réelle et que ce type de régime était bien accepté dans telle population. De plus, nous avons montré que l’augmentation du rapport SDS/glucides était associée à une amélioration du contrôle glycémique postprandial et qu’il existait une corrélation linéaire inverse entre les paramètres de VG et la teneur en SDS. La mise en œuvre d’un régime riche en amidon lentement digestible dans une population atteinte de DT2, a montré une différence significative sur le profil de variabilité glycémique, mais également sur les excursions glycémiques postprandiales, évalués par le CGMS, en comparaison avec un régime pauvre en amidon lentement digestible. Ce type de régime a également permis aux patients d’atteindre des cibles glycémiques postprandiales plus appropriées. Grâce à un travail de revue de la littérature, nous avons mis en évidence que la déviation standard (SD), le coefficient de variation (CV), l’amplitude moyenne des excursions glycémiques (MAGE) et la moyenne glycémique (MBG) étaient les paramètres de VG les plus étudiés en termes de relation avec les paramètres de diagnostic du DT2 et les complications liées au DT2 et qu’ils montraient des relations fortes, en particulier avec l’HbA1c. Dans les études interventionnelles, nous avons pu voir que la SD, le MAGE et le temps dans la cible (TIR) étaient les paramètres les plus utilisés comme critères d’évaluation, montrant des améliorations significatives suite aux interventions pharmacologiques ou nutritionnelles, souvent en lien avec des paramètres de contrôle glycémique comme l’HbA1c, la glycémie à jeun ou en postprandial. La VG apparaît donc comme une composante clé de la dysglycémie du DT2. Au-delà de son utilisation par le patient comme support du contrôle glycémique, le CGMS apparait comme un outil pertinent en recherche clinique pour évaluer l’efficacité des interventions même si à ce jour, il reste encore très peu utilisé pour les interventions nutritionnelles. Des études plus approfondies seront cependant nécessaires pour confirmer l'impact bénéfique de telles interventions alimentaires à long terme. Nous avons conçu une étude à plus grande échelle pour étudier l'impact à long terme d’un régime riche en SDS sur la variabilité et le contrôle glycémiques (CGMS) et les complications et comorbidités associées chez le patient atteint de DT2. La modulation de la digestibilité de l'amidon dans l'alimentation pourrait alors être utilisée comme un outil nutritionnel simple et approprié pour améliorer l'homéostasie glucidique au quotidien dans le DT2.
... Starch that is slowly digested in vitro elicits low glycaemic and insulinaemic responses in vivo (8,9) , effects that are generally considered to be beneficial (10,11) . The glycaemic impact of dietary starch is influenced by its chemical structure (12) , which depends on plant variety (13,14) and its physico-chemical properties such as the degree of starch gelatinisation (15,16) , food matrix (17) and particle size (18,19) , and may be altered by chemical or enzymatic treatment (20) , food processing (21,22) and by the addition of fat and protein (23)(24)(25) . Englyst et al. proposed that the glycemic impact of foods could be explained by their content of rapidly available glucose (RAG, the amount of glucose from rapidly digested starch and free sugars that is rapidly available for absorption) and slowly available glucose (SAG, the amount of glucose from slowly digested starch and free sugars that is slowly available for absorption) (26,27) . ...
Article
Full-text available
Dietary starch contains rapidly (RAG) and slowly available glucose (SAG). To establish the relationships between the RAG:SAG ratio and postprandial glucose, insulin and hunger, we measured postprandial responses elicited by test meals varying in the RAG:SAG ratio in n 160 healthy adults, each of whom participated in one of four randomised cross-over studies ( n 40 each): a pilot trial comparing six chews (RAG:SAG ratio 2·4–42·7) and three studies comparing a test granola (TG1-3, RAG:SAG ratio 4·5–5·2) with a control granola (CG1–3, RAG:SAG ratio 54·8–69·3). Within studies, test meals were matched for fat, protein and available carbohydrate. Blood glucose, serum insulin and subjective hunger were measured for 3 h. Data were subjected to repeated-measures analysis of variance (ANOVA). The relationships between the RAG:SAG ratio and postprandial end points were determined by regression analysis. In the pilot trial, 0–2 h glucose incremental areas under the curve (iAUC0–2; primary end point) varied across the six chews ( P = 0·014) with each 50 % reduction in the RAG:SAG ratio reducing relative glucose response by 4·0 %. TGs1-3 elicited significantly lower glucose iAUC0–2 than CGs1–3 by 17, 18 and 17 %, respectively (similar to the 15 % reduction predicted by the pilot trial). The combined means ± sem ( n 120) for TC and CG were glucose iAUC0–2, 98 ± 4 v . 118 ± 4 mmol × min/l ( P < 0·001), and insulin iAUC0–2, 153 ± 9 v . 184 ± 11 nmol × h/l ( P < 0·001), respectively. Neither postprandial hunger nor glucose or hunger increments 2 h after eating differed significantly between TG and CG. We concluded that TGs with RAG:SAG ratios <5·5 predictably reduced glycaemic and insulinaemic responses compared with CGs with RAG:SAG ratios >54. However, compared with CG, TG did not reduce postprandial hunger or delay the return of glucose or hunger to baseline.
Article
Background Starch's digestibility in foods strongly depends on the structure, other ingredients, and processing conditions used. This study aimed to investigate the effect of psyllium fiber on gelatinization, crystallinity, and in vitro digestibility of starches having different crystalline structures (A, B, and C). Wheat, potato, and tapioca starches with and without added psyllium fiber were heated at 90°C for 10 min at three different solid: water (w:v) ratios (1:1, 1:2, and 1:5). The added fiber content was 50% (dry base) in the solid fraction for the fiber added samples. Results Wheat, potato, and tapioca starches showed different structural, morphological, and starch digestibility properties. The effect of cooking and fiber addition on starch digestion differed for the starch types, mainly wheat starch. Psyllium addition during cooking decreased the rapidly digestible starch (RDS) fractions while increasing the slowly digestible starch (SDS) and remaining/resistant starch (RS) fractions. The effect of psyllium fiber addition was not limited to restricting the swelling and gelatinization of starch granules during heating. Psyllium fiber effectively restricted the mobility of digestive enzymes during digestion. Conclusions Understanding the relationship between psyllium and starch digestibility for different types of starch could assist in designing food formulations with lower starch digestibility. These in vitro data, however, should be confirmed by in vivo studies. This article is protected by copyright. All rights reserved.
Article
As an important staple food, grain is subject to substitution and adulteration with cheaper cereals. Therefore, verification of authenticity is an issue for flour. In this work, Raman spectroscopy was used as non-invasive technique to discriminate the species barley, rye, spelt and wheat. In total, 129 samples with different origins and varieties from two harvest years were used as training data. Principal component analysis and partial least-squares discriminant analysis showed a clear differentiation of the species (accuracies >98%). Quality control of anomalous spectra improved the classification accuracy with Mahalanobis distance and Hotelling’s T² and Q residuals statistics proving superior to manual selection. Validation with 86 independent samples including an additional harvest year per species corroborated the feasibility of discrimination (accuracy: 88%) and shows the impact of the variety and harvest year. The discrimination of the spectra was primarily based on starch, protein and arabinoxylan signals.
Chapter
Whole grains or whole grain foods contain “all the essential parts and naturally-occurring nutrients of the entire grain seed in their original proportions” and its carbohydrates include endosperm starch and non-starch polysaccharides, and minor amounts of inulin and simple sugars. A good understanding of the mechanism and role carbohydrates play in the health benefits associated with whole grain foods is a necessary basis to develop strategies to optimize their impact in unprocessed and processed foods. Low gastrointestinal is equated with a slow digestion property of starch that moderates and extends glycemic response. Food structure is a key factor affecting starch digestion, and any disruption of the physical or botanical structure of cereal grains can increase rate of digestion and postprandial glycemic response. Dietary fibres can slow the absorption of glucose or other nutrients from both its physiochemical property such as high viscosity and the ileo-colonic brake systems, which enhance carbohydrate quality of whole grain foods.
Chapter
This chapter reviews the evidence for an association between intake of whole grains and both total and cause-specific mortality. It presents issues pertaining to dietary patterns and human intervention studies and cardiovascular mortality and cancer mortality. The results of the studies of cardiovascular mortality or ischemic heart disease mortality display some more variability than for total mortality, but the results are based on fewer cases of death per study. The prospective cohort studies report a fairly consistent decrease in total mortality, regardless of whether they studied single whole grain products or total whole grains, and at different levels of intake. Results from both a priori and a posteriori studies of dietary patterns have suggested that whole grains play a role as a part of a healthful dietary pattern. Antioxidants, dietary fibre and many phytochemicals in the whole grain contribute to its anti-inflammatory properties.
Chapter
Consumption of whole grain has been suggested to decrease the risk of obesity, indicated by a decreased weight or weight gain in prospective studies. Appetite sensation may be affected during or immediately after whole grain consumption, potentially mediated by mechanisms related to stomach distension or a lower glycemic response. Various single-meal studies have investigated the effects of different types of whole grain products on subjective appetite sensation and ad libitum energy intake at a subsequent meal in acute settings. The presence of dietary fibre and resistant starch as well as the firmer botanical structure of whole grain foods may impair digestion and absorption in the small intestine, which increases the passage of macronutrients to the colon. Factors such as dietary fibre content and composition, particle size and cereal type may determine effects on appetite. Consumption of certain whole grain foods has been reported to influence appetite sensation after the following meal, the so-called “second-meal effect.”
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A case control study of gall stone disease in relation to diet, alcohol, and relative weight was undertaken. The study population comprised 267 hospital patients with newly diagnosed gall stone disease, 241 individually matched controls selected from the community, and 359 controls who were patients in hospital. Dietary intake was estimated with a quantitative food frequency questionnaire. Multiple logistic regression analysis was used to estimate the net association between individual nutrients and the risk of formation of gall stones. Variations in risk with sex and age were examined in the light of prior evidence of influences of sex hormones and age on hepatobiliary metabolism. In both sexes increased intake of alcohol was associated with a decreased risk of developing gall stones; increased intake of simple sugars in drinks and sweets was associated with an increased risk; and increased intake of energy or fat was associated with an increased risk in young subjects. Obesity was associated with an increased risk only in young women.
Article
The availability for digestion of starch in vitro after flaking, steam cooking and popping of whole grain wheat was studied and compared with that of raw and boiled wheat. Some physical and morphological characteristics were also investigated and correlated with starch availability for amylolysis. In an in vitro assay using hog pancreatic α-amylase after preincubation with pepsin, starch in flaked wheat was less available than that in boiled, popped and steam-cooked wheat. The starch in raw wheat was digested only slightly. When pepsin was omitted, the availability to α-amylase of starch in raw and boiled wheat decreased substantially, indicating that a large fraction of the starch was encapsulated in a protein matrix. The starch in flaked wheat elicited lower plasma glucose and plasma insulin levels in rats in vivo than that in boiled wheat after a gastric load. With raw wheat, the plasma glucose peak was much delayed and of lower magnitude compared with that with the heat-treated samples. In order to obtain good agreement with the in vivo results, a pepsin step had to be included in the in vitro assay using α-amylase. Differential scanning calorimetry measurements indicated that starch in flaked wheat was not gelatinised completely and this fact probably accounted for the lower availability in flaked wheat compared with boiled, popped or steam-cooked wheat.
Article
After accurate determination of the content of available carbohydrate in a wide variety of cereals, as in vitro method was used to study factors that influence hydrolysis rates of starch in foods. Fiber, physical form, cooking, and the possible presence of a natural amylase inhibitor were all shown to affect hydrolysis rates of starch. Fiber only exerted an inhibiting effect on the rate of hydrolysis when it formed a physical barrier to limit access of the hydrolytic enzymes to the starch (as in whole brown rice, for example). Particle size played an important role in determining the rate of hydrolysis. Cooking made the starch much more readily available for enzymic hydrolysis presumably by gelatinizing it. Stoneground wholemeal flour was hydrolyzed more slowly than white flour. This is consistent with the presence of a natural amylase inhibitor that has been isolated from wheat germ in the whole grain. Our results suggest that such amylase inhibitor activity is destroyed by passage through the roller mill, since the starch in wheat germ and standard wholemeal flour (i.e., not stoneground but reconstituted after passage through the roller mill) was hydrolyzed at a rate identical to white flour.
Article
Oral glucose-tolerance tests (G.T.T.s) with serum - immunoreactive - insulin (I.R.I.) measurements were done on a " diabetic " Tamil Indian family, on members of a Cape Coloured population who screened positive on urine and capillary-blood testing, and on controls. The more potentially diabetic a group became, the higher the fasting insulin level and the greater the insulin response, whether this potentiality was indicated by overweight, borderline G.T.T.s, or diabetic parentage, and however the insulin response was expressed. However, when chemical diabetes appeared, the I.R.I. response was reduced and delayed. It is concluded that, with regard to oral glucose stimulation in these two population groups, the earliest biochemical lesion is associated with insulin excess rather than insulin deficiency.
Article
We have studied the effects of glucose, sucrose, and various starches on postprandial plasma glucose and insulin responses in 19 subjects. All carbohydrate loads were calculated to contain 50 gm. of glucose, and the response to each carbohydrate was tested twice: when given alone in a drink or when given in combination with other nutrients as a meal. The data demonstrate: (1) Glucose and sucrose elicited similar plasma glucose response curves, but sucrose elicited a somewhat greater (20 per cent) plasma insulin response. (2) Raw starch ingestion resulted in a 44 per cent lower glucose response and a 35-65 per cent lower insulin response than did either glucose or sucrose ingestion. (3) When carbohydrate was given as a meal the plasma glucose responses were 40-60 per cent lower than when the same carbohydrate was given as a drink, while the insulin responses were generally similar, and (4) when different cooked starches were compared, the plasma glucose and insulin responses to rice were significantly lower (50 per cent) than to potato. In conclusion, the size of the carbohydrate molecule appears to influence the postprandial glucose and insulin responses such that more complex carbohydrates (starches) elicit lower responses. This effect may be related to differences in digestion rather than to differences in absorption.
Article
The digestion and absorption of dietary starch and nonstarch polysaccharides (NSP) in the small intestine of man from oats, cornflakes, and white bread has been determined by feeding seven ileostomists test meals containing these foods and estimating carbohydrate recovery in the effluent. NSP, the main constituent of dietary fiber, was almost completely recovered from all three test meals, including the water soluble beta-glucan which is the main NSP in oats. Less than 0.6% of the starch in oats was recovered as starch with a further 1.2% as dextrins and maltose. 4% of cornflake starch however was recovered, of which the main part was resistant to alpha-amylase digestion in vitro unless specially dispersed. Similarly with white bread 2.5% of ingested starch reached the terminal ileum of which the greater part was starch resistant to alpha-amylase in vitro. Overall 5.8% of the carbohydrate in white bread, 5.3% in cornflakes, and 11.7% in oats was recovered. This study supports the view that human digestive enzymes do not break down dietary NSP. It also identifies a fraction of starch, RS, present in processed food which resists breakdown by alpha-amylase both in vitro and in the small intestine of man.
Article
The polysaccharide content of some cereal foods is reported, measured by a recently described technique. This method allows accurate determination of plant cell wall and other plant polysaccharides and identification and measurement of starch made resistant to digestion by α-amylase and pullulanase during food processing (resistant starch). The results reported are at variance with values for dietary fibre measured by other published methods by a factor of up to 10 in some foods. This is due partly to the failure of some methods to identify resistant starch separately from NSP and partly to other details of methodology. Implied in these findings is the need to critically assess methods used for the chemical determination of non-starch polysaccharides and the need to be cautious in interpreting dietary-fibre-intake data especially in population studies.
Article
The responses of serum glucose and insulin to both cooked and raw starch were studied in 11 healthy men. Serum insulin values rose less after starch, whether raw or cooked, than after an equivalent load of glucose. That the response of insulin after cooked starch was less than after glucose suggests that viscosity of the meal was involved, whereas the greater reduction in the response of insulin to raw starch was unlikely to have had a viscosity component. Thus, both dietary fibre type and cooking can alter the response.