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G
lycemic
Response to Pasta: Effect of
Surface
Area, Degree of Cooking, and
Protein
Enrichment
T.
M. S.
WOLEVER, BM, MSc,
D. J. A.
JENKINS, DM,
J.
KALMUSKY, RPDt,
C.
GIORDANO, RPDt,
S.
GIUDICI, RPDt,
A.
L.
JENKINS, RPDt,
L. U.
THOMPSON, PhD,
G. S.
WONG, MD, AND
R. G.
JOSSE,
MD
To
see whether food form, the degree of
cooking,
or protein enrichment affected the glycemic response
to
pasta, we gave test-meal breakfasts to 13 diabetic patients. Macaroni had a significantly greater
glycemic
index (GI) (68 ± 8) than spaghetti (45 ± 6, P < .01); the GI of star pastina was intermediate
(54
± 6). The GI of spaghetti was not significantly affected by cooking for 5 or 15 min (45 ± 6 and
46
± 5, respectively), or by protein enrichment (38 ± 4). The GI of spaghetti was similar in 11 non-
insulin-dependent
and 6 insulin-dependent diabetic patients (49 ± 7 compared with 57 ± 8). We
conclude
that different types of pasta may produce different glycemic responses but that these are not
necessarily
related to differences in cooking or surface area,
DIABETES
CARE
1986;
9=401-404.
T
here is much interest in the glycemic responses to
carbohydrate foods in diabetic patients.1"8 Many
factors affect the glycemic response to meals: im-
portant among these are the food form,69 particle
size,
10
'
11
protein content of the meal,12 and the degree of
cooking.713 Pasta is a popular starchy food, which, in the
form of spaghetti, has been shown to have a low glycemic
response, ~60% that of bread.4'6 However, there are many
different types of pasta available, and each type may have
potentially different metabolic effects because of different sur-
face areas and protein contents. In addition, the traditional
Italian method of cooking pasta
is
different from that in North
America; the Italians prefer their pasta relatively under-
cooked, or "al dente." We have therefore investigated the
effect on the glycemic response in diabetic patients of five
different forms of pasta: "overcooked" spaghetti, "under-
cooked" spaghetti, macaroni, star pastina (small pasta stars),
and protein-enriched spaghetti.
METHODS
Seventeen diabetic patients who had no evidence of gastro-
paresis were studied. Six were classified as insulin dependent
(IDDM: fasting C peptide <0.6 ng/ml with no postprandial
rise) and 11 as non-insulin dependent (NIDDM). Charac-
teristics of the IDDM and NIDDM subjects, respectively,
were
as
follows:
age, 50 ± 6 and 70 ±
2
yr; ideal body weight,
107 ± 5 and 129 ± 10%; duration of diabetes, 19 ± 4 and
10 ± 2 yr; mean fasting blood glucose, 8.7 ± 0.8 and
7.2 ± 0.5 mmol/L; and mean HbAlc, 8.2 ± 0.7 and
6.7 ± 0.4%. The IDDM patients took a mean of
31
± 5 U
of insulin per day. Seven of the NIDDM patients were treated
with insulin (mean 28 ± 11 U/day), three with oral hypo-
glycemic agents, and one with diet only. Fasting fingerprick
capillary blood samples were obtained (Autolet lancets, Owen
Mumford, Woodstock, Oxford, UK). Five minutes after the
patients took their usual insulin or other diabetes medications
(if any), a test meal was given. Fingerprick blood samples
were obtained every 30 min for 3 h after the start of each
meal for measurement of whole blood glucose with an au-
tomatic analyzer (Model 27, Yellow Springs Instruments, Yel-
low Springs, OH).
Test
meals.
Test-meal constituents and cooking methods
are shown in Table 1. White flour and the uncooked spaghetti
were analyzed for nutrient14 and dietary fiber content.15 Mac-
aroni and star pastina were assumed to have the same com-
position as the spaghetti from the same manufacturer.
Each test meal contained 50 g available carbohydrate from
white bread or pasta. For palatability, all the test meals were
served with 32 g cheddar cheese plus 100 g cooked tomato.
Each subject also took at least three test meals of white bread
only (mean 5.6 ± 0.7, range 3-12).
The test meals were consumed in random order. Four of
the IDDM subjects were unable to complete all the tests and
were given only the 5-min spaghetti test meal. Because no
significant difference in the glycemic response to spaghetti
DIABETES
CARE, VOL. 9 NO. 4, JULY-AUGUST 1986
401
GLYCEMIC RESPONSE TO PASTA/T. M. S. WOLEVER AND ASSOCIATES
TABLE 1
Test-meal constituents, cooking methods, and mean ± SE glycemic indices
FoodDry wt
(g)Cooking methodGlycemic index'
White bread
White bread + C + Tt
5-min spaghetti§ + C + T
15-min spaghetti§ + C + T
Macaroni§ + C + T
Star pastina§ + C + T
Spaghetti|| + C + T
(protein-enriched)
67.0t
67.
Ot
66.0
66.0
66.0
66.0
66.3
Baked in diet kitchen
Baked in diet kitchen
Boiled, 180 ml water, 5 min
Boiled, 300 ml water, 15 min;
frozen, reheated before test
Boiled, 180 ml water, 5 min
Boiled, 180 ml water, 5 min
Boiled, 180 ml water, 7 min
100A
99 ± 4A
45 ± 6B
46 ± 6B
64 ± 8C
54 ± 6BC
38±4
R
Excess water from cooking was consumed with the test meals.
'Means not sharing the same letter superscript are significantly different (P < .01).
tWeight of flour. $C = 32 g mild cheddar cheese, T = 100 g cooked tomato. §Lancia-Bravo Foods Ltd., Toronto, Canada; ||Catelli Plus, Catelli Ltd.,
Montreal, Canada.
was found between IDDM and NIDDM subjects, the results
of 2 IDDM subjects who completed all the test meals were
pooled with the results of the 11 NIDDM subjects.
The study was approved by the human experimentation
ethics committee of the University of Toronto.
Data
analysis.
The glycemic indices (GIs) of the test meals
were calculated using the three white bread tests taken closest
to the date of each test meal, which has been shown to
minimize the variability of GI calculations.16 Results are ex-
pressed as means ± SE. The dimensions of uncooked pasta
were measured and the surface areas calculated by appropriate
formulas. Incremental areas under the blood glucose response
-O White bread
-#-
White bread plus cheese and tomato
60 120
Time (min)180
FIG. I. Mean ± SE blood glucose responses of 13 diabetic patients
(I I NIDDM and 2 IDDM) who took meals of white bread containing
50 g available carbohydrate or same amount of white bread with 32 g
cheddar cheese plus 100 g cooked tomato.
curves were calculated geometrically using the blood glucose
increments.17 Any area beneath the fasting blood glucose
level was ignored. After demonstration of significant heter-
ogeneity by two-way analysis of variance,18 the means were
compared using Fisher's test (if F > 10) or Tukey's test (if
F < 10). The significance of the differences for the six IDDM
patients who tested spaghetti and bread was assessed by Stu-
dent's t test for paired data.
RESULTS
Effect of added cheese and tomato. The effect on the glycemic
response of adding cheese and tomato to bread was negligible
(Fig. 1, Table 1). Therefore, no adjustment for added cheese
and tomato was made to the GI of the pasta meals.
Effect
of
type
of pasta. The mean glycemic responses to the
pasta meals were significantly lower than those to the bread
meals (Fig. 2, Table 1). The GI of spaghetti was significantly
lower than that of macaroni (P < .01). The glycemic re-
sponses to star pastina and protein-enriched spaghetti were
not significantly different from those to regular spaghetti (Fig.
2,
Table 1).
Effect of
cooking.
Cooking spaghetti for 5 or 15 min had
virtually no impact on the mean glycemic response (Fig. 2)
orGI (Table 1).
Comparison of IDDM with NIDDM subjects. IDDM and
NIDDM subjects responded similarly to spaghetti cooked for
5 min, or "al dente" (Fig. 3). The GIs for spaghetti in IDDM
(57 ± 8, N = 6) and NIDDM (49 ± 7, N = 11) patients
were not significantly different.
DISCUSSION
T
he results confirm the low GI of pasta.6 In addition,
they indicate that differences exist in the glycemic
response to different forms of pasta; these differ-
ences are not necessarily related to the surface area,
the degree of cooking, or protein enrichment.
Surface area has been ascribed an important role in deter-
402DIABETES CARE, VOL. 9 NO. 4, JULY-AUGUST 1986
GLYCEMIC RESPONSE TO PASTA/T. M. S. WOLEVER AND ASSOCIATES
O-White Bread
-A- Star Pastina
Macaroni
Spaghetti
-O White Bread -#- Enriched Spaghetti
Spaghetti -Q- 15min Spaghetti
60 120
Time (min)180
FIG.
2.
Mean
± SE
blood glucose responses
of 13
diabetic patients
(11 N/DDM and
2
IDDM) who took meals of white
bread,
macaroni,
star pastina,
5-min
("aldente")
spaghetti,
15-min {overcooked) spaghetti,
or protein-enriched
spaghetti.
For each time, means not sharing same letter
are significantly different
(P < .01).
mining the rate of digestion of starch, which, in turn, is
related to the glycemic response.19 Increasing the surface area
by grinding rice, for example, has been associated with an
increased rate of enzymatic hydrolysis and enhanced glycemic
and endocrine responses.1011 Although the surface areas of
the 66-g portions of uncooked spaghetti, macaroni, and star
pastina were quite different
(0.11,
0.091,
and 0.14 m2, re-
spectively), they did not relate to the glycemic response. This
was probably because the surface areas would have been in-
creased to different extents by chewing.
Starch produces a greater glycemic response when cooked
than when consumed raw,713 presumably because cooking
increases the degree of starch gelatinization and its suscep-
tibility to enzymatic digestion. In this study, the difference
between cooking spaghetti for 5 or 15 min was not reflected
in a different glycemic response, despite the fact that the
"overcooked" spaghetti was frozen and reheated as well as
cooked for a longer period of time and was, therefore, much
softer than the 5-min spaghetti. Nevertheless, our "over-
cooked" spaghetti may not have been overcooked enough to
see the true effect of the very-overcooked pasta that is some-
times eaten in North America (e.g., canned pasta).
The addition of protein to meals has been found to increase
insulin secretion and reduce the glycemic response12 only
when relatively large amounts of protein (30-50 g protein/
50
g
carbohydrate) are used. The lack of effect of added cheese
and tomato (containing 9.1 g protein) or of protein-enriched
spaghetti (2.3 g more protein than the portion of regular
o-White bread
-•- Aldente spaghetti
IDDM
60 120
Time (min)180
FIG.
3.
Mean
±
SE blood glucose responses of 6 IDDM subjects (top
panel) and JJ NIDDM
subjects
(bottom panel) who took meab of
white bread or "al dente" spaghetti.
DIABETES CARE, VOL. 9 NO. 4, JULY-AUGUST 1986403
GLYCEMIC RESPONSE TO PASTA/T. M. S. WOLEVER AND ASSOCIATES
spaghetti) on the glycemic response was probably due to the
small amounts of protein added.
We conclude that pasta has a significantly lower GI than
bread. However, different types of pasta have different gly-
cemic responses that are not necessarily related to surface
area, the degree of cooking, or protein enrichment.
ACKNOWLEDGMENTS:
T.M.S. W. received a Fellowship from the
Kellogg's Company, Battle Creek, Michigan. These studies
were supported by the Natural Sciences and Engineering Re-
search Council of Canada.
From the Department of Nutritional Sciences, Faculty of Med-
icine (T.M.S.W., D.J.A.J., J.K., C.G., S.G., A.L.J., L.U.I.); and
the Division of Endocrinology and Metabolism, St. Michael's Hos-
pital (T.M.S.W., D.J.A.J., G.S.W., R.G.J.), University of Toronto,
Toronto, Ontario M5S 1A8, Canada.
Address reprint requests to Dr. Thomas M. S. Wolever at the
above address.
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