Download The glycaemic index of potatoes: the effect of variety

European Journal of Clinical Nutrition (1999) 53, 249±254
ß 1999 Stockton Press. All rights reserved 0954±3007/99 $12.00
http://www.stockton-press.co.uk/ejcn
The glycaemic index of potatoes: the effect of variety, cooking
method and maturity
NL Soh1 and J Brand-Miller1*
1
Human Nutrition Unit, Department of Biochemistry, the University of Sydney, NSW, 2006, Australia
Objective: The aim of this study was to determine the impact of variety, cooking method and maturity on the GI
of potatoes, it was hypothesised that new potatoes may have a relatively lower GI.
Design and subjects: Ten healthy volunteers were recruited as subjects through advertising on the campus of the
University of Sydney. Equal (50 g) carbohydrate portions of eight potato meals (three varieties, four cooking
methods, two states of maturity) and two reference white bread meals were fed in random order to each of the
subjects over a period of 10 weeks. Capillary blood samples were taken in the fasting state and then at 15, 30, 45,
60, 90 and 120 min from the start of each meal. Samples were analysed for plasma glucose concentrations and
incremental areas under plasma glucose curves were calculated. The GI of the potato was calculated as the AUC
of the potato expressed as a percentage of the individual's average AUC of the white bread. This was then
multiplied by 0.7 to index the GI to glucose as the reference food.
Results: GI values (mean s.e.m.) ranged from 65 9 (canned new potatoes) to 101 15 (boiled Desiree
potatoes), glucose ˆ 100. No signi®cant difference was found among the three varieties of potato tested
(P ˆ 0.38) or among the four different cooking methods (P ˆ 0.55). The GI values of the canned new potato
and boiled Desiree potato were signi®cantly different (P ˆ 0.047). The average size of the tuber was found to
correlate with the GI (r ˆ 0.83, P < 0.05).
Conclusions: Potatoes, regardless of variety, cooking method and maturity, have exceptionally high GI values.
New potatoes have relatively lower GI values which is attributed to differences in starch structure.
Sponsors: University of Sydney.
Descriptors: glycaemic index; food; starch; digestion; potatoes
Introduction
The glycaemic index (GI) is a method of ranking foods
according to their postprandial blood glucose response with
respect to that of an equicarbohydrate portion of a reference
food (Wolever et al, 1994). The GI is relevant in both
preventing and managing diabetes mellitus. Two six-year
cohort studies, one in men (SalmeroÂn et al, 1997a) and one
in women (SalmeroÂn et al, 1997b) have demonstrated that
diets with high glycaemic load=low cereal ®bre content are
linked with more than twice the risk of non-insulin dependent diabetes mellitus (NIDDM) when compared to diets
with low glycaemic load=high cereal ®bre content. Hence,
a diet with a low glycaemic index may help prevent
NIDDM. Cross-over studies in NIDDM patients have
shown that decreasing dietary GI leads to improved glycaemic control (Wolever et al, 1992; Brand et al, 1991),
similar to that achieved by hypoglycaemic drugs.
Studies have also shown improved lipidaemic control
with low GI diets in NIDDM and hyperlipidaemic subjects
(Wolever et al, 1992). Establishing and maintaining acceptable plasma lipid levels is important in diabetes management as the disease carries a greater risk of developing
cardiovascular disease (Anderson & Geil, 1994). Cardiovascular disease has also been directly linked to serum
insulin levels (DespreÂs et al, 1996; Salonen et al, 1998).
*Correspondence: Prof J Brand-Miller, Human Nutrition Unit, Department
of Biochemistry G08, University of Sydney NSW 2006, Australia.
Received 30 June 1998; revised 27 October 1998; accepted 6 November
1998
Low GI diets have been shown to decrease fasting and
postprandial insulin responses (Wolever et al, 1991; DAA,
1997) and improve insulin sensitivity in patients with
advanced coronary heart disease (Frost et al, 1996).
The potato (Solanum tuberosum) generally has one of
the highest GI values of any food, although some types
such as `new' potatoes appear to be lower than others. The
published GI values for potatoes vary from as low as 56 to
as high as 85 (on a scale where glucose ˆ 100) for reasons
which are not clear and when centres of study are compared, the potato is the food which yields the most variable
glycaemic response (Wolever, 1990). Furthermore, the
variety of the potato investigated is often not speci®ed,
leading to some confusion over the impact of variety vs
preparation method.
The GI of potatoes needs to be clari®ed because they
make a major contribution to total starch intake. In industrialised countries, potatoes contribute about 15 ± 20% of
total starch intake compared with bread, another staple,
which contributes about 35% (English et al, 1987). Given
the popularity of the potato, a low GI variety and=or
cooking method could signi®cantly lower the overall glycaemic load of the western diet, this in turn may decrease
the risk of NIDDM.
The aim of this present study was to determine the
differences in GI between the more popular varieties of
potatoes commonly sold on international markets and the
effects of different cooking methods on GI. Emphasis was
placed on determining the true available carbohydrate
content of the different potatoes studied, as opposed to
The glycaemic index of potatoes
NL Soh and J Brand±Miller
250
reliance on tables of food composition. It was hypothesised
that new potatoes may have a relatively lower GI due to
differences in starch structure affected by maturity.
Materials and methods
Subjects
Ten healthy volunteers (eight female and two male) were
recruited through advertisements placed around The University of Sydney campus. The study was approved by the
Medical Ethics Committee of The University of Sydney
and all volunteers gave written informed consent. Mean
age s.d. was 25 7 y and mean body mass index s.d.
was 22.8 2.8. Before each test, subjects fasted for 10 h
overnight, during which time consumption of water was
permitted. To avoid the `second meal effect' (Wolever et
al, 1988), they were instructed not to eat legumes in the
meal preceding the fast. Alcohol was limited to two drinks
the day before each test and a similar meal was eaten before
each fast.
On the morning of each test, two ®nger-prick capillary
blood samples were collected ®ve minutes apart to determine baseline glucose levels. Foods were eaten at 0 min
time and over the 2 h following the start of each test meal,
1 ml capillary blood samples were collected at 15, 30, 45,
60, 90 and 120 min. To enhance peripheral blood circulation to the ®ngers, subjects warmed their hands with hot
water bottles for approximately 5 min before each blood
sampling. Blood samples were taken using an Autoclix1
device (Boehringer Mannheim, Australia), collected into
1.5 ml microcentrifuge tubes coated with heparin (10 IU
heparin sodium salt, Sigma Chemical Co., St Louis, USA)
and immediately centrifuged at 12 000 g for 30 s. The
plasma was removed and stored at 720 C for later
analysis.
Test foods
Eight test meals and two reference food meals (white
bread) were given to each subject in randomised order
over a 10 week period. White bread (Tip Top1 Sunblest1,
Sydney, Australia) was chosen as the reference food over
the original glucose as it was considered to be a more
physiological standard (Wolever, 1990). Fresh potatoes
were purchased from Sydney retail supermarkets, in bulk
quantities suf®cient to conduct all tests; canned new potatoes (EdgellTM Mint Tiny TatersTM, Edgell-Birdseye, Melbourne, Australia) were donated by Cowra Export Packers
Ltd. The three varieties of potato chosen for testing were
the major varieties grown for the Australian fresh market
(Kirkham, 1995) and also featured in international markets
in the United Kingdom and United States, namely, Sebago,
Desiree and Pontiac. Fresh new potatoes and canned new
potatoes were tested because immature potatoes are known
to contain starch with different amylose to amylopectin
ratios (Brunt and Zinsmeester, unpublished data). Four
methods of cooking were assessed using one variety, that
is Pontiac: boiled, boiled and mashed, oven-baked and
microwaved. All tests were conducted on the peeled
potato, except in the case of fresh boiled new potatoes
which are generally eaten with the skin intact. Therefore, in
total, eight different potato meals, each containing 50 g
available carbohydrate (starch and sugars) were fed to all
10 subjects. Water was used to make up the meal volume to
750 ml in each case.
Available carbohydrate contents of the fresh potatoes
were analysed using a previously described method (Wills
et al, 1980). Brie¯y, a homogenised food sample is
extracted with methanol and ®ltered, the extract is analysed
for sugar content by HPLC while the starch in the residue is
hydrolysed with amyloglucosidase before also being analysed for sugar content by HPLC. The available carbohydrate content of the food is provided by the sum of the
sugars in the extract and the residue. This method excludes
most resistant starch. Carbohydrate contents for the reference white bread and the canned new potatoes were taken
from manufacturers' information. Table 1 shows the carbohydrate contents of the foods and the weight of 50 g
carbohydrate portions. The average weights per tuber s.d.
(unpeeled) for Sebago, Desiree, Pontiac and new potatoes
were 196 66 g, 188 64 g, 91 28 g and 73 20 g. The
average weight in the canned product was 33 g, the range
being 22 ± 45 g.
Fresh potatoes were peeled, weighed out, dipped for 30 s
in a 0.1% sodium metabisulphite solution to prevent
browning and stored covered in the refrigerator overnight.
To avoid starch retrogradation, potatoes were freshly
cooked each morning. Potatoes were cooked until soft
and large potatoes were halved before cooking. Potatoes
for boiling were heated to 100 C in an excess of boiling
water and then boiled for 35 min. New potatoes were left
unpeeled, the skins pricked with a fork and added to an
excess of already boiling water and boiled for 20 min.
Potatoes for mashing were cut into 1 ± 2 cm cubes, heated
to 100 C in an excess of boiling water and boiled for
15 min. The potato was then drained and mashed with a
fork. In all the potato meals subjected to the boiling
process, the cooking liquid was included in the water
balance of the meal.
Potatoes for baking were prepared by wrapping the
peeled potatoes individually in aluminium foil and baking
them at 190 C in a gas oven for 25 min. Potatoes for
microwaving were placed in a covered ceramic dish and
microwaved at full power (650 W) for 6 ± 7.5 min. The
canned new potatoes were drained, weighed out on the
morning of each test and microwave-heated at full power
for 3 min before serving.
Plasma glucose analysis
Plasma samples, stored at 720 C, were thawed at room
temperature, vortexed and centrifuged before analysis for
glucose concentration. Photometric analyses were conducted in duplicate on a Cobas Fara centrifugal analyser
(Roche Diagnostica, Basle, Switzerland) using a hexokinase=glucose-6-phosphate dehydrogenase method (Unimate 5
Gluc HKTM, Roche Diagnostic Systems, Frenchs Forest,
Australia). All plasma samples pertaining to the one food
Table 1 Carbohydrate (CHO) content of the foods tested based on the
raw product with the exception of canned potatoes
Food
CHO (g=100 g)
1
1
Tip Top ; Sunblest
White bread
Sebago, peeled
Desiree, peeled
New, unpeeled
Pontiac, peeled
Canned new, drained
Available
portion (g)
Weight of 50 g CHO
balance (ml)
Water
43.8
114
620
11.0
11.2
14.0
12.1
12.0
454
446
358
414
416
315
325
415
355
360
The glycaemic index of potatoes
NL Soh and J Brand±Miller
251
were analysed at the same time. Inter- and intra-assay
coef®cients of variance were 1.16% and 1.45%
respectively.
Calculation of GI
The incremental areas under the plasma glucose curves
(AUC) were determined for each food according to standardised criteria (Wolever et al, 1991), ignoring any area
below the baseline. The average AUC for the two white
bread tests was used as the reference value and each
subject's individual GI for each food was calculated. The
GI for each food was taken as the average of all 10
individual values. This was then multiplied by 0.7 to
convert the value to one indexed to glucose, GI ˆ 100
(Foster-Powell & Brand Miller, 1995).
Statistical analyses
The glycaemic responses of the two reference white bread
tests were compared using a paired t-test. Two-way analysis of variance was used to compare GI values between
potato varieties (boiled Sebago, Pontiac and Desiree),
between cooking methods (baked, boiled, mashed and
microwaved Pontiac potatoes) and between the new potatoes and the potato variety with the highest GI. The
correlation coef®cient between GI value and tuber weight
was determined, the level of signi®cance was taken as
P < 0.05.
Results
The GI of the products tested is shown in Table 2, no
statistically signi®cant difference was found among the GI
of the different varieties of potato (Sebago, Pontiac and
Desiree) (P ˆ 0.38, Figure 1) nor among the various cooking methods (boiled, baked, microwaved and mashed
Pontiac potato) (P ˆ 0.55, Figure 2). The only signi®cant
difference was between the canned new potato and boiled
Desiree potato (P ˆ 0.047, Figure 3). The GI of the three
mature varieties and two `new' potato products correlated
with their average tuber weight (r ˆ 0.83, P < 0.05, Figure
4).
Discussion
This study con®rms that potatoes, irrespective of variety,
cooking method or maturity, have exceptionally high GI
Table 2 GI values of test foods s.e.m. (n ˆ 10, except n ˆ 9 for new
potatoes, canned and microwave-heated)
Food
Variety
Sebago, peeled and boiled
Desiree, peeled and boiled
Pontiac, peeled and boiled
Cooking method
Pontiac, peeled and boiled
Pontiac, peeled, boiled
and mashed
Pontiac, peeled and microwaved
Pontiac, peeled and baked
Maturity
New, unpeeled and boiled
New, canned and microwave
heated
GI s.e.m.
GI s.e.m.
(white bread ˆ 100) (glucose ˆ 100)
124 10
144 22
125 13
87 7
101 15
88 9
125 13
130 13
88 9
91 9
112 13
133 15
79 9
93 11
112 17
93 13
78 12
65 9
Figure 1 Top: Incremental glycaemic response to potatoes by variety.
Bottom: Glycaemic index of potatoes by variety s.e.m. (glucose ˆ 100),
none of the differences is statistically signi®cant.
values, with one case equivalent to that of a 50 g glucose
load (Desiree, boiled: GI ˆ 101 15). Current nutritional
advice to increase the intake of starchy foods such as
potatoes may therefore lead to a diet with increased
glycaemic load and hence greater risk of NIDDM (SalmeroÂn et al, 1997a, 1997b).
In the literature, there is a wide range of GI values for
boiled potatoes, from as low as 56 to as high as 85. Because
the variety is usually not speci®ed, it is not possible to
determine whether this is the source of the variation. In this
present study, the GI of boiled Pontiac potatoes was 88,
which is 32 units higher than a previously published value
of 56 (Brand et al, 1985). Such discrepancies may be
largely attributed to the use of different food composition
data when calculating the serving size of the food (Jenkins
et al, 1988). For example, published carbohydrate content
for peeled, boiled new potatoes varies from 12.8 g=100 g
(English & Lewis, 1991) to 17.8 g=100 g (Holland et al,
1991). This results in 50 g carbohydrate portion sizes of
391 g and 281 g respectively, a difference of nearly 30%. In
this present study we used 414 g of Pontiac potato, fresh
weight while the previous study speci®ed 294 g of boiled
Pontiac potato based on data from food tables (Brand et al,
1985), this difference alone can account for the discrepancies
in GI values.
The glycaemic index of potatoes
NL Soh and J Brand±Miller
252
Figure 2 Top: Incremental glycaemic response to Pontiac potato by
cooking method. Bottom: Glycaemic index of Pontiac potato by cooking
method s.e.m. (glucose ˆ 100), none of the differences is statistically
signi®cant.
Authorities differ in their conclusions regarding the
impact of cooking methods on the GI of potatoes. In this
present study, there were no signi®cant differences in GI of
Pontiac potatoes whether they were boiled, oven-baked,
microwaved or mashed. In contrast, Lunetta et al (1995)
found that baked potatoes produced a signi®cantly lower
incremental glycaemic response compared with boiled
potatoes, even when the same amounts of fat were added
to each. They concluded that the baking process led to less
cooking of the internal part of the potato and reduced the
potato's digestibility. Wolever et al (1994), like us, found
no signi®cant differences between baked, boiled and
canned potatoes. However, they found that mashing signi®cantly increased the glycaemic response (by 15 ± 20%).
On the other hand, Englyst & Cummings (1987) found that
starch digestibility of cooled potato was identical when
eaten as large lumps or ®nely sieved twice, implying that
the glycaemic response is unlikely to be affected.
Our study showed no effect of cooking method on the GI
of just one variety of potato (Pontiac). This does not
necessarily imply that other potato varieties will behave
in the same way. However, we can think of no scienti®c
reason why there might be differences. Cooking methods
Figure 3 Top: Incremental glycaemic response to canned new potato,
boiled new potato and Desiree potato. Bottom: Glycaemic index for
canned new potato, boiled new potato and Desiree potato s.e.m.
(glucose ˆ 100).
Figure 4 Correlation between average weight of potato tuber and GI
( s.e.m.).
The glycaemic index of potatoes
NL Soh and J Brand±Miller
involving `moist heat' (mashing, baking, microwaving) are
likely to affect different varieties in similar ways. Potato
starch gelatinises at 55 ± 66 C (Crapo et al, 1981) which is
well below the temperatures involved in baking and boiling
potatoes. Furthermore, fresh potato tubers contain suf®cient
water to fully gelatinise their starch contents when heattreated (Kingman & Englyst, 1994) and resistant starch
granules are unlikely to remain in potatoes cooked using
conventional domestic methods. To avoid differences in
resistant starch content as a result of cooling, we served all
the products immediately after cooking (or heating in the
case of the canned product).
Both boiled new potatoes and canned new potatoes had
the lowest GI values of the potatoes tested, the difference
reaching statistical signi®cance when compared with the
highest GI potato. In absolute terms, the average GI of
canned potatoes was almost 36% less, a difference that is
probably biologically important. The relatively lower
values of the new potatoes may be due to differences in
starch structure. As potatoes mature, the quantity of amylose increases but the difference is small and not likely to
affect the glycaemic response (Brunt & Zinsmeester,
unpublished data). On the other hand, the degree of
amylopectin branching signi®cantly increased with the
maturity of the potato. Amylopectin has an irregular,
branching structure and is more readily gelatinised than
the linear amylose molecule leading to a higher glycaemic
effect (Wolever, 1990). We speculate that the lower GI of
new potatoes may be due to reduced amylopectin branching
and hence greater resistance to gelatinisation. Canned new
potatoes may be more immature again as the typical size is
smaller: the average weight of the fresh new potato was
73 g while that of the canned was only 33 g. To test the
hypothesis that the size of the potato in¯uenced the GI (via
differences in maturity and starch structure), we determined
the correlation between GI and the average size of the
potato tuber in our study (Figure 4). The r value of 0.83
(P < 0.05) suggests that the starch of more mature potatoes
is easier to digest, leading to a higher GI.
The unintentional inclusion of some resistant starch in
the 50 g available carbohydrate portion of canned new
potatoes might also have contributed to its low GI. The
carbohydrate content of this product was provided by the
manufacturer who used the `carbohydrate by difference'
method (calculated by substracting the percentages of
water, protein, fat, ash and dietary ®bre from 100). The
manufacturer used the AOAC method (Prosky et al, 1988)
of measuring dietary ®bre which includes some but not all
resistant starch (RS). In the published literature, the RS of
cold canned new potatoes is 6.8% of total starch but reheating reduces this to 1.4% (Kingman & Englyst, 1994).
The canned new potatoes in our study had a total starch
content of 11.6 g=100 g drained weight. Hence, of the 50 g
carbohydrate portion served, 48.3 g was starch of which
1.4% may have been RS ˆ 0.7 g. This small amount would
not account for all of the difference between the GI of the
canned new potatoes and the mature potatoes.
The very high GI values of the potatoes tested begs the
question: is the potato an `undesirable' food? Foods containing glucose are not recommended to people with
diabetes because of their assumed potential to cause hyperglycaemia. Potatoes are still recommended in diabetes due
to their low fat and high micronutrient content. Their high
satiety (Holt et al, 1995) may also bene®t NIDDM patients
as weight control is often part of their treatment. Despite its
status as a high carbohydrate food, the potato is relatively
low when compared with most cereal foods: close 0.4 kg
was needed to achieve the 50 g carbohydrate portions used
in this study. It is unlikely that such an amount would
normally be consumed in one sitting and this would affect
the glycaemic response in the usual setting. Nonetheless, to
achieve a prescribed goal in carbohydrate (200 g) or
number of exchanges (12), potatoes could well contribute
to an exceptionally high glycaemic load, this, in turn, may
increase insulin demand and exacerbate insulin resistance.
It is possible that `wild' or less domesticated varieties of
potato have lower GI values than current ones. Starchy
vegetables which were important foods in the diets of some
Australian Aborigines (for example, cheeky yam (Discorea
bulbifera), pencil yam (Vigna lanceolata), bush potato
(Ipomoea costata)) and Paci®c Islanders (for example,
sweet potato (Ipomoea batatas)) have been shown to be
digested more slowly than Western starchy staples (Thorburn et al, 1987a). and to produce signi®cantly lower
glycaemic responses when compared to Sebago potatoes
(Thorburn et al, 1987a, 1987b). Given the popularity of the
potato and its extraordinarily high GI, it may be valuable to
manipulate the genotype of wild or cultivated varieties of
potato to yield a commercially viable low GI potato.
Conclusions
Neither variety nor cooking method appears to have
marked effects on the GI of potatoes tested in this current
study. Apparent differences among varieties in the literature may be methodological artifacts resulting from differences in assumed carbohydrate content. Apart from the
canned variety, all the potatoes tested in the present study
had high GI values (GI > 78). The lower GI of canned new
potato (GI ˆ 65) may result from differences in starch
structure in immature potatoes but may also be due to
unintentional inclusion of some resistant starch in the 50 g
carbohydrate portion. The lower GI of canned new potatoes
is probably of suf®cient magnitude to be clinically important in the dietary management of diabetes. The correlation
between the average size of the potatoes and their GI needs
to be con®rmed in further studies.
Acknowledgements ÐWe are grateful to Cowra Export Packers Ltd who
donated the canned new potatoes, Edgell-Birdseye, Australia who provided nutritional information and the volunteers who undertook the ten
weeks of GI testing.
References
Anderson JW & Geil PB (1994): Nutritional management of diabetes
mellitus. In Modern Nutrition in Health and Disease. In Vol 2, 8th edn,
ME Shils, JA Olson & M Shike (eds.) Philadelphia: Lea and Febiger. pp
1259 ± 1286.
Brand JC, Colagiuri S, Crossman S, Allen A, Roberts DCK & Truswell AS
(1991): Low-glycemic index foods improve long-term glycemic control
in NIDDM. Diabetes Care 14, 95 ± 101.
Brand JC, Nicholson PL, Thorburn, AW & Truswell AS (1985): Food
processing and the glycemic index. Am. J. Clin. Nutr. 42, 1192 ± 1196.
Crapo PA, Insel J, Sperling M & Kolterman OG (1981): Comparison of
serum glucose, insulin and glucagon responses to different types of
complex carbohydrate in noninsulin-dependent diabetic patients. Am. J.
Clin. Nutr. 34, 184 ± 190.
DespreÂs JP, Lamarche B, MaurieÁge P, Cantin B, Dagenais GR, Moorjani S
& Lupien PJ (1996): Hyperinsulinemia as an independent risk factor for
ischemic heart disease. N. Engl. J. Med. 334, 952 ± 957.
Dietitians Association of Australia (1997): Glycaemic index in diabetes
management. Aust. J. Nutr. Diet. 54, 57 ± 63.
253
The glycaemic index of potatoes
NL Soh and J Brand±Miller
254
English R, Cashel K, Bennett S, Berzins J, Waters A & Magnus P (1987):
National Dietary Survey of Adults: 1983ÐNo. 2 Nutrient Intakes. 29.
Canberra: Australian Government Publishing Service.
English R & Lewis J (1991): Nutritional Values of Australian Foods.
Canberra: Australian Government Publishing Service, pp 31 ± 32.
Englyst HN & Cummings JH (1987): Digestion of polysaccharides of
potato in the small intestine of man. Am. J. Clin. Nutr. 45, 423 ± 431.
Foster-Powell K & Brand Miller J (1995): International tables of glycemic
index. Am. J. Clin. Nutr. (suppl) 62, S871 ± S890.
Frost G, Keogh B, Smith D, Akinsanya K & Leeds A (1996): The effect of
low-glycemic carbohydrate on insulin and glucose response in vivo and
in vitro in patients with coronary heart disease. Metabolism 45,
669 ± 672.
Holland B, Unwin ID & Buss DH (1991): Vegetables, Herbs and Spices.
5th Supplement to McCance and Widdowson's The Composition of
Foods 4th Edition, 10 ± 15. Cambridge: Royal Society of Chemistry and
Ministry of Agriculture, Fisheries and Food.
Holt SHA, Brand Miller JC, Petocz P & Farmakalidis E (1995): A satiety
index of common foods. Eur. J. Clin. Nutr. 49, 675 ± 690.
Jenkins DJA, Wolever TMS & Jenkins AL (1988): Starchy foods and
glycemic index. Diabetes Care 11, 149 ± 159.
Kingman SM & Englyst HN (1994): The in¯uence of food preparation
methods on the in-vitro digestibility of starch in potatoes. Food
Chemistry 49, 181 ± 186.
Kirkham R (1995): Potatoes. In: Horticulture Australia: The Complete
Reference of the Australian Horticultural Industry. B Coombs (ed.)
Hawthorn East, Victoria: Morescope Publishing, pp.250 ± 256.
Lunetta M, Di Mauro M, Crimi S & Mughini L (1995): In¯uence
of different cooking processes on the glycaemic response to
potatoes in non-insulin dependent diabetic patients. Diab. Nutr.
Metab. 8, 49 ± 53.
Prosky L, Asp N-G, Schweizer TF, DeVries JW & Furda I. (1988):
Determination of insoluble, soluble and total dietary ®ber in foods
and food products interlaboratory study. J. Assoc. Off. Anal. Chem. 71,
1017 ± 1023.
SalmeroÂn J, Ascherio A, Rimm, EB, Colditz GA, Spiegelman D, Jenkins
DJ, Stampfer MJ, Wing AL & Willett WC (1997a): Dietary ®ber,
glycemic load, and risk of NIDDM in men. Diabetes Care 20, 545 ±
550.
SalmeroÂn J, Manson JE, Stampfer MJ, Colditz GA, Wing AL & Willett
WC (1997b): Dietary ®ber, glycemic load, and risk of non-insulindependent diabetes mellitus in women. JAMA 277, 472 ± 477.
Salonen JT, Lakka TA, Lakka HM, Valkonen VP, Everson SA & Kaplan
GA (1998): Hyperinsulinemia is associated with the incidence of
hypertension and dyslipidemia in middle-aged men. Diabetes 47,
270 ± 275.
Thorburn AW, Brand JC & Truswell AS (1987a): Slowly digested and
absorbed carbohydrate in traditional bushfoods: a protective factor
against diabetes? Am. J. Clin. Nutr. 45, 98 ± 106.
Thorburn AW, Brand JC, O'Dea K, Spargo RM & Truswell AS (1987b):
Plasma glucose and insulin responses to starchy foods in Australian
Aborigines: a population now at high risk of diabetes. Am. J. Clin. Nutr.
46, 282 ± 285.
Wills RBH, Balmer N & Green®eld H (1980): Composition of Australian
foods. 2. Methods of analysis. Food Technol. Australia 32, 198 ± 204.
Wolever TMS (1990): The glycemic index. World Rev. Nutr. Diet. 62,
120 ± 185.
Wolever TMS, Jenkins DJA, Jenkins AL & Josse RG (1991): The
glycemic index: methodology and clinical implications. Am. J. Clin.
Nutr. 54, 846 ± 854.
Wolever TMS, Jenkins DJA, Ocana AM, Rao VA & Collier GR (1988):
Second-meal effect: low-glycemic-index foods eaten at dinner improve
subsequent breakfast glycemic response. Am. J. Clin. Nutr. 48,
1041 ± 1047.
Wolever TMS, Jenkins DJA, Vuksan V, Jenkins AL, Wong GS & Josse
RG (1992): Bene®cial effects of low-glycemic index diet in overweight
NIDDM subjects. Diabetes Care 15, 562 ± 564.
Wolever TMS, Katzman-Relle L, Jenkins AL, Vuksan V, Josse RG &
Jenkins DJA (1994): Glycaemic index of 102 complex carbohydrate
foods in patients with diabetes. Nutr. Res. 14, 651 ± 669.