
FoodgroupAgeBMI2yFruit
(n = 5 F, 6 M)22.9
±3.922.9
±1.4Bakery
products (n = 6 F, 6 M)22.2
±3.723.1 ±2.7Snacks
andconfectionery(n = 5 F, 7 M)21.0
±1.222.9 ±3.5Protein-rich
foods (n 5 F, 6 M)22.4
±2.824.3 ±3.1Carbohydrate-rich
foods (n = 5 F, 8 M)21.0
±1.923.0 ±1.9Breakfast
cereals (n = 5 F, 6 M)22.8
±3.922.8
±1.4
1268
HOLT ET AL
tube radioimmunoassay kit (Coat-A-Count; Diagnostic Prod
ucts Corporation, Los Angeles). For both plasma glucose and
insulin analysis, all nine plasma samples for a particular sub
ject's test were analyzed within the same run to reduce any
error introducedby interassayvariation.When possible,all
plasma samples for a particular subject were analyzed for
insulin within the same run. For the insulin analysis, the mean
within-assay CV was 5% and the mean between-assay CV was
7%.
Statistical analysis
Cumulative changes in postprandial plasma glucose and
insulin responses for each food were quantified as the incre
mental area under the 120-mn response curve (AUC), which
was calculated by using the trapezoidal rule with fasting con
centrations as the baseline and truncated at zero. Any negative
areas tended to be small and were ignored. For each subject, an
IS (%) was calculated for each test food by dividing the insulin
AUC value for the test food by the insulin AUC value for white
bread (the reference food), and expressed as a percentage as
follows:
IS (%)
Area under the 120-mm insulin response
curve for 1000 U test food
Areaunderthe 120-mminsulinresponsecurve
for 1000 Id white bread
TABLE 3
Characteristics of each group of subjects'
‘¿I ± SD.
2 In kg/rn2.
a reference food controls for inherent differences between
individuals that affect insulin sensitivity, such as body weight
and activity levels.
Subjects were fed 1000-U portions of the test foods in a
random order on separate mornings after a 10-h overnight
fast. Within each food group, each subject acted as his or her
own control, being tested at the same time of day and under
as similar conditions as possible. Subjects were asked to
refrain from unusual activity and food intake patterns, to
abstain from alcohol and legumes the day before a test, and
to eat a similar meal the night before each test. When
subjects arrived at the lab in the morning, they completed a
short questionnaire assessing recent food intake and activity
patterns. A fasting finger-prick blood sample was collected
and subjects were then given a test food and 220 mL water
(0 mm). When possible, foods were presented under a large
opaque plastic hood with a hole through which volunteers
pulled out pieces of the test food one at a time. This was an
attempt to minimize between-subject variation in cephalic
phase insulin secretion arising from the sensory stimulation
associated with the anticipation and act of eating (27).
However, this was not feasible for the liquid foods (yogurt
and ice cream), foods served in a sauce (baked beans and
lentils), or with milk (all of the breakfast cereals), which
were presented in standard bowls without the hood.
Subjects were asked to eat and drink at a comfortable rate.
Immediately after finishing the test food, subjects recorded the
time taken to eat the food and completed a questionnaire
assessing various appetite responses and the food's palatability.
[These results are reported in a separate paper (28).] Subjects
remained seated at tables in a quiet environment and were not
permitted to eat or drink until the end of the session (120 mm).
Finger-prick blood samples (1.5—2.5mL) were collected
from warmed hands immediately before the meal (0 mm) and
15, 30, 45, 60, 75, 90, 105, and 120 mm after the start of the
meal (into plastic tubes that had been kept on ice) with use of
an automatic lancet device (Autoclix; Boehringer Mannheim
Australia, Castle Hill, Australia). Blood samples were centri
fuged immediately after collection (1 miii at 12 500 X g at
room temperature) and plasma was pipetted into chilled tubes
and immediately stored at —¿20°Cuntil analyzed (< 1 mo).
Plasma glucose concentrations were analyzed in duplicate with
a Cobas Fara automatic spectrophotometric analyzer (Roche
Diagnostica, Basel, Switzerland) and the glucose hexokinase
enzymatic assay. The mean within-assay and between-assay
precisions (CVs) were both < 6%. Plasma insulin concentra
tions were measured in duplicate by using an antibody-coated
X100 (1)
This equation is similar to that developed by Wolever and
Jenkins (29) for calculating GI values. A glucose score (GS)
(not the same as a GI score, which is based on a 50-g carbo
hydrate portion) for each food was also calculated by using the
same equation with the corresponding plasma glucose results.
Analysis of variance (ANOVA) and Fisher's probable least
significant-difference test for multiple comparisons were used to
determine statistical differences among the foods within each food
group (STATVIEW STUDENT SOFFWARE; Abacus Concepts
mc, Berkley, CA). Linear-regressionanalysis was used to test
associations between glucose and insulin responses and nutritional
indexes (MINITAB DATA ANALYSIS SOFFWARE, version
7.0; Minitab Inc, State College, PA). Test foods not containing a
particular nutrient were excluded from these analyses. Therefore,
sample sizes for the correlations between individual nutrients and
the mean GSs and ISs varied from 32 to 36. Mean results for white
bread for each food group were included in some statistical anal
yses, so these correlations were made with 43 values. One subject
from the protein-rich food group did not complete the fish test and
one subject from the breakfast cereal group did not complete the
Sustain test. Therefore, in total, 503 indiVidUal tests were fully
completed.
Stepwise-multiple-regression analysis was used to examine
the extent to which the different macronutrients and GSs ac
counted for the variability of the ISs (MINITAB DATA
ANALYSIS SOFTWARE). For this analysis, the individual
white bread OS and IS results were included for the carbohy
drate-rich food group only; therefore, this analysis was per
formed with 446 individual observations for 38 foods. Includ
ing the white bread results for each food group (n = 503)
suggests that independent repeat tests were done for white
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