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The Glycemic Index
(GI) is an important theoretical concept in attempting
to understand nutritional processes. It is a number
(usually in the range 10 to 100) characteristic for
a particular type of food, relating to how quickly your
blood-sugar level goes up after you eat some of that
food. This property varies greatly between different
foods.
For a long introductory article on the Glycemic Index,
see:
http://members.lycos.co.uk/ramendosa/gidigest.htm
In general the ideal is a low
index-figure, which implies that blood-sugar level rises
only slowly, i.e. that the food is digested slowly.
In such a case the body's digestive system has time
to deal with the food in the most appropriate fashion.
This may be compared to the "delayed release"
capsules available for some drugs; and in fact one author
goes so far as to suggest that one should regard food
as a drug whose prime function is to control blood-sugar
level.
Low GI (slow change of blood-sugar level) is
especially important for sufferers from diabetes, since
in this disease the body's normal regulatory mechanism
for blood-sugar does not function correctly; and inappropriate
levels, over the long-term, cause many consequential
problems. Conversely, a regular diet of high-GI foods
(such as high-sugar foods), tends to be associated with
just these kind of problems -- and may in fact have
a causative role in the development of diabetes. This
disease is now extremely common in "developed"
countries, and its incidence seems to be increasing
It is also suggested that low-GI foods may be beneficial
in providing a greater feeling of satiety, thus discouraging
overeating and helping to avoid the development of obesity.
Unfortunately however, there are at present a number
of limitations, and the Glycemic Index is less useful
for practical purposes than one might hope. Some of
the problems are discussed below.
As might be expected,
eating a dose of sugar makes the blood-sugar level increase
almost immediately. After about 2 hours however (if
no more food is eaten), the blood-sugar level reaches
a peak and then slowly declines as the body deals with
this "fuel" intake. Other types of food, such
as legumes, tend to be digested more slowly and the
peak level is lower and "flatter". A rapidly-digested
food such as sugar is normally employed as a convenient
reference-standard.
The usual test-procedure is that after a pre-test fasting
period (commonly 8 hours), a standard amount of the
food (commonly 80 grams) is eaten; and at a given time
(2 hours) after eating, the blood-sugar concentration
(mg/100ml) is measured. This figure is then compared
to the level found 2 hours after a "standard"
meal, commonly the same weight of glucose (or sometimes
white bread, which like glucose is digested quickly).
The ratio of the two concentrations, expressed as a
percentage, is the Glycemic Index for that type of food.
(Sometimes a more sophisticated measure is used in which
the blood-sugar level is measured at several different
times and the "area under the curve" (AUC)
is calculated.)
Another figure sometimes
quoted is Glycemic Load (GL). This is simply the amount
of carbohydrate in the food eaten (e.g. in the test-meal
used to measure GI), in grams, "scaled" by
multiplying by the GI. So if the 80g test-meal contained
4g of carbohydrate, and the GI for that food was 50
(%), or 0.5, the Glycemic Load would be 2 (grams).
The thought behind this is that one would like to be
able to assess the effect on blood-sugar of "real"
food-intake, and such effect obviously depends on the
amount eaten, not just the type of food. More specifically,
the effect is presumed to depend mainly on the amount
(and type) of carbohydrate, since the other food components,
protein and fat, are digested much more slowly. Extending
the idea, one might calculate the GL figure for each
(carbohydrate) component of a given meal, and add them
up to give the total GL; which could be thought of as
the weight of "pure" sugar which would be
expected to produce an equivalent blood-sugar effect.
Because of the limitations
of our present state of knowledge, however, the apparent
exactness implied by GI figures is rather deceptive
(see below). General guidelines, rather than mathematical
precision, are probably the most one should expect.
Originally it was assumed
that a clear-cut distinction could be made between the
glycemic effects of different types of carbohydrates
as classified according to well-known categories; sugars
versus starches, or on the basis of size of molecule
-- "simple" carbohydrates (e.g. sugar) versus
"complex" carbohydrates (as found e.g. in
whole-grains). But it has turned out that in practice
it is not really possible to predict in advance which
foods will have high or low GI values. Current research
thus falls back on a descriptive classification into
"RAC" and "SAC" ("rapidly available"
and "slowly available") carbohydrate types;
but it is not yet clear just what is the crucial factor
causing this difference.
- Sugary foods generally have high
GI.
- Legumes (e.g. beans, lentils)
generally have low GI.
- Raw foods have lower GI than the
same foods when cooked.
- Less-processed foods have lower
GI than the processed version (e.g.
whole-grains compared to flour) .
Here we sketch some
of the factors which at present tend to limit the usefulness
of available Glycemic Index data
As can be seen from
the outline description already given, GI measurement
is a somewhat tedious process; and (as usual for bio-measurements)
one needs to take the average result for a large number
of persons. Experiments thus usually compare a rather
limited range of foods, in a given study. For this reason,
and of course as a reliability check, to get an overall
picture we need to use data from many different sources.
But there are a number of important factors which are
unfortunately often not the same between different investigations,
and which may make the results not directly comparable.
Here are a few examples of such difficulties, which
can be particularly misleading for those lacking scientific
training:
- The high-GI "standard"
food (GI=100) is often glucose, but sometimes another
food is used. If this is clearly stated, then a
correction-factor can be applied -- but some authors
neglect to do this.
- The amount of the meal is often
80g, but sometimes 100g or some other figure. (And
in this regard one could perhaps ask whether it
would not be better to use, instead of a fixed absolute
amount, an amount constant in some other aspect,
e.g. in proportion to the test-person's body-weight.
To overcome this problem, a different measure called
"Glycemic Glucose Equivalent" (GGE) has
been proposed. But there is at present little published
data giving GGE figures.)
- The time of measurement is commonly
2 hours after the test-meal, but in some cases 3
hours; and the pre-test fasting period may also
vary.
- The number of persons tested
has a great influence on the accuracy of the result.
So a test on 100 persons, producing a GI result
of (say) 30, might (or might not) be in fact consistent
with a test on only 5 persons which came up with
a GI result of 50. To decide, one needs to know
more details.
- Food from different sources (e.g.
crops grown in different conditions or in different
regions) may have different properties.
- The exact cooking or processing
method of the test-food may be of great significance,
but this can be difficult to standardise between
different investigations.
But
perhaps the most significant problem is that a great
proportion of the GI investigations have been carried
out on diabetic patients (because of its practical importance
in this disease). It appears highly problematic to try
and compare GI figures found in such patients, where
the blood-sugar metabolism is known to be disturbed
(and where, also, the type and severity of the disease
may differ widely), with figures found in tests on non-diabetic
subjects.
In the early days,
when relatively few measurements had actually been made,
ambitious "ranking" tables for various foods
with (as it now appears) somewhat spurious apparent
precision were constructed. In fact, given the tendency
of many authors to copy uncritically (or even blindly)
from each other, much of this potentially misleading
data is still around today, and still presented as "gospel".
But all the above
factors, and no doubt others as well, mean that for
a given type of food one will often find quite wildly
different GI figures quoted (e.g. for carrots, 16% to
80%; for bread, 40% to 85%). Some of these apparent
discrepancies may be resolvable by assessing the exact
details of the investigations concerned -- provided
these can be found.
Even if the above-mentioned
incompatibilities of different measurements could be
standardised or allowed for, there is another fundamental
difficulty in making practical use of GI figures.
In experiments, the
investigator usually tries to simplify the conditions
as much as possible. But in real life one will in most
cases eat not just one food alone (after a standard
fasting period), but rather a series of meals each combining
several different foods.
As mentioned above,
the "Glycemic Load" concept on the face of
it does offer a simple way of calculating the combined
effect. But, unfortunately, this simple addition procedure
is not necessarily a reliable predictor. The different
foods interact in complex ways, and the real rate of
absorption is characteristic of that particular combination.
For example, it is found that the fat component of a
meal -- not directly taken account of in the GL calculation
-- tends to slow the rise in blood-sugar. Even food-additives
which in themselves have little or no nutritional value
can modify the glycemic effect. It has also been shown
that certain foods eaten some time previously can markedly
influence the glycemic impact of the current meal --
but there may be no effect if the foods are both consumed
at the same time.
Some interesting and
valuable work has been done to compare the overall glycemic
effect of "typical" meals, in a few relatively
simple cases; but then of course the problems of comparability
between different studies are even more difficult.
The whole field is
the subject of ongoing research. No doubt in due ourse
matters will become clearer; but at present, although
the glycemic effect of food intake is an important (but
often neglected) aspect which certainly deserves serious
consideration, caution seems appropriate in using published
GI data as a precise guide in diet-planning.
If you nevertheless want to check out reported findings
for various foods, here are a few interesting links:
http://www.mendosa.com/common_foods.htm
[Classifies common
foods into high/ medium/ low-GI groups.]
www.calvin.biochem.usyd.edu.au/GIDB/searchD3.htm
[Database with results
of tests for a large number of foods, quoting journal
references and other details.]
http://members.lycos.co.uk/ramendosa/gilists.htm
[Edited version of
the above database.]
In summary, Glycemic
Index is undoubtedly an important factor to bear in
mind when trying to optimise your diet -- but the well-known
proverb has literal relevance here: "The proof
of the pudding is in the eating!" Let practical
experience be your ultimate guide.
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Department of Medicine, Children's
Hospital, Boston, Massachusetts 02115, USA.
Prevalence rates of overweight
and obesity have risen precipitously in the United States
and other developed countries since the 1960s, despite
comprehensive public health efforts to combat this problem.
Although considerable attention has been focused on
decreasing dietary fat and increasing physical activity
level, the potential relevance of the dietary glycemic
index to obesity treatment has received comparatively
little scientific notice. This examines how the glycemic
and insulinemic responses to diet may affect body weight
regulation, and argues for the potential utility of
low glycemic index diets in the prevention and treatment
of obesity and related complications.
PMID: 12733742
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Department of Studies in Food Science
& Nutrition, University of MysoreManasagangotri, Mysore
570 006, India.
In the present study the effect
of processing on starch fractions (rapidly digestible
starch (RDS), slowly digestible starch (SDS) and resistant
starch) were measured, using controlled enzymic hydrolysis
with pancreatin and amyloglucidase, in six rice varieties;
namely, BT rice, Gauri rice, Sona masoori, parboiled
rice, Salem parboiled rice, and steamed rice. The processes
studied were pressure cooking, boiling, steaming and
straining. Rapidly available glucose (RAG) was also
measured to derive a Starch Digestion Index (SDI). Cooking
of rice by different methods decreased the amylose content.
The degree of gelatinization ranged from 56 to 95, with
pressure cooking resulting in the maximum degree. The
starch fractions varied depending on the cooking method.
Significant inverse correlations were seen between RDS
and SDS (r = 0.40, P < 0.05), and between amylose and
SDI (r = 0.60, P < 0.01). RAG and RDS related positively
(r = 0.90, P < 0.01). The SDI of rice varieties cooked
by the boiling and straining method were significantly
higher (P < 0.05). The results emphasize that cooking
methods influence the nutritionally important starch
fractions in rice varieties.
PMID: 12701235
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Department of Internal Medicine,
Faculty of Medicine and Biomedical Sciences University
of Yaounde 1, Cameroon.
OBJECTIVE: To evaluate glycaemic
and insulinaemic index and in vitro digestibility of
the five most common Cameroonian mixed meals consisting
of rice+tomato soup (diet A), bean stew+plantains (B),
foofoo corn+ndole (C)yams+groundnut soup (D), and koki
beans+cassava (E). SUBJECTS: Ten healthy non-obese volunteers,
aged 19-31 y, with no family history of diabetes or
hypertension. INTERVENTIONS: A 75 g oral glucose tolerance
test followed by the eating of the test diets with carbohydrate
content standardized to 75 g every 4 days with blood
samples taken at 0, 15, 30, 60, 120 and 180 min. In
vitro digestion of each diet according to Brand's protocol.
MAIN OUTCOME MEASURES: Plasma glucose, cholesterol,
triglyceride, insulin and C-peptide, with calculation
of glycaemic and insulinaemic index defined as the area
under the glucose and insulin response curve after consumption
of a test food divided by the area under the curve after
consumption of a control food containing the same amount
of carbohydrate, and digestibility index. RESULTS: Glycaemic
index (GI) varied from 34.1 (diet C) to 52.0% (diet
E) with no statistical difference between the diets,
and insulinaemic index varied significantly from 40.2%
(C) to 70.9% (A) (P=0.03). The digestibility index varied
from 18.9 (C) to 60.8% (A) (P<0.0001), and did not correlate
with glycaemic or insulinaemic indices. However, carbohydrate
content correlated with GI (r=0.83; P=0.04), digestibility
index (r=-0.70; P<0.01), and insulinaemic index (r=0.91;
P<0.01). Plasma C-peptide and plasma lipids showed little
difference over 180 min following the ingestion of each
meal. CONCLUSIONS: Glycaemic index of these African
mixed meals are relatively low and might not be predicted
by in vitro digestibility index.
PMID: 12700620
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Department of Family and Preventive
Medicine, University of Utah, Salt Lake City, Utah,
USA.
Simultaneous consideration of
the influence of the different types of carbohydrates
and fats in human diets on mortality rates (especially
the diseases of aging), and the probable retardation
of such diseases by caloric restriction (CR) leads to
the hypothesis that restriction of foods with a high
glycemic index and saturated or hydrogenated fats would
avoid or delay many diseases of aging and might result
in life extension. Many of the health benefits of CR
might thereby be available to humans without the side
effects or unacceptability of semi-starvation diets.
PMID: 12699727
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Englyst Carbohydrates - Research
& Services Ltd, 2 Venture Road, Chilworth Science Park,
Hampshire SO16 7NP, UK.
Elucidating the role of carbohydrate
quality in human nutrition requires a greater understanding
of how the physico-chemical characteristics of foods
relate to their physiological properties. It was hypothesised
that rapidly available glucose (RAG) and slowly available
glucose (SAG), in vitro measures describing the rate
of glucose release from foods, are the main determinants
of glycaemic index (GI) and insulinaemic index (II)
for cereal products. Twenty-three products (five breakfast
cereals, six bakery products and crackersand twelve
biscuits) had their GI and II values determined, and
were characterised by their fat, protein, starch and
sugar contents, with the carbohydrate fraction further
divided into total fructose, RAG, SAG and resistant
starch. Relationships between these characteristics
and GI and II values were investigated by regression
analysis. The cereal products had a range of GI (28-93)
and II (61-115) values, which were positively correlated
(r(2)) 0.22, P<0.001). The biscuit group, which had
the highest SAG content (8.6 (SD 3.7) g per portion)
due to the presence of ungelatinised starch, was found
to have the lowest GI value (51 (SD 14)). There was
no significant association between GI and either starch
or sugar, while RAG was positively (r(2)) 0.54P<0.001)
and SAG was negatively (r(2)) 0.63, P<0.001) correlated
with GI. Fat was correlated with GI (r(2)) 0.52, P<0.001),
and combined SAG and fat accounted for 73.1% of the
variance in GI, with SAG as the dominant variable. RAG
and protein together contributed equally in accounting
for 45.0 % of the variance in II. In conclusion, the
GI and II values of the cereal products investigated
can be explained by the RAG and SAG contents. A high
SAG content identifies low-GI foods that are rich in
slowly released carbohydrates for which health benefits
have been proposed.
PMID: 12628028
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Department of Nutritional Sciences,
University of Toronto, Toronto, Ontario, Canada.
OBJECTIVE:: Practical use of the
glycaemic index (GI), as recommended by the FAO/WHO,
requires an evaluation of the recommended method. Our
purpose was to determine the magnitude and sources of
variation of the GI values obtained by experienced investigators
in different international centres. DESIGN:: GI values
of four centrally provided foods (instant potato, rice,
spaghetti and barley) and locally obtained white bread
were determined in 8-12 subjects in each of seven centres
using the method recommended by FAO/WHO. Data analysis
was performed centrally. SETTING:: University departments
of nutrition. SUBJECTS:: Healthy subjects (28 male,
40 female) were studied. RESULTS:: The GI values of
the five foods did not vary significantly in different
centres nor was there a significant centrexfood interaction.
Within-subject variation from two centres using venous
blood was twice that from five centres using capillary
blood. The s.d. of centre mean GI values was reduced
from 10.6 (range 6.8-12.8) to 9.0 (range 4.8-12.6) by
excluding venous blood data. GI values were not significantly
related to differences in method of glucose measurement
or subject characteristics (age, sex, BMI, ethnicity
or absolute glycaemic response). GI values for locally
obtained bread were no more variable than those for
centrally provided foods. CONCLUSIONS:: The GI values
of foods are more precisely determined using capillary
than venous blood sampling, with mean between-laboratory
s.d. of approximately 9.0. Finding ways to reduce within-subject
variation of glycaemic responses may be the most effective
strategy to improve the precision of measurement of
GI values.European Journal of Clinical Nutrition (2003)
57, 475-482. doi:10.1038/sj.ejcn.1601551
PMID: 12627186
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Center for Pediatric Nutrition
Research, Department of Pediatrics, School of Medicine,
University of Utah, Salt Lake City 84132, USA.
BACKGROUND: One in 5 American
children is overweight, despite a decrease in total
fat consumption. This has sparked an interest in the
carbohydrate composition of diets, including the glycemic
index (GI). OBJECTIVE: To investigate whether a low-GI
meal replacement (LMR) produced similar metabolichormonal,
and satiety responses in overweight adolescents as a
low-GI whole-food meal (LWM) when compared with a moderately
high-GI meal replacement (HMR). METHODS: Randomized,
crossover study comparing LMR, HMR, and LWM in 16 (8
male/8 female) adolescents during 3 separate 24-hour
admissions. The meal replacements consisted of a shake
and a nutrition bar. Identical test meals were provided
at breakfast and lunch. Metabolic and hormonal indices
were assessed between meals. Measures of participants'
perceived satiety included hunger scales and ad libitum
food intake. RESULTS: The incremental areas under the
curve for glucose were 46% and 43% lower after the LMR
and LWM, respectively, compared with the HMR. Insulin's
incremental area under the curve was also significantly
lower after both low GI test meals (LMR = 36%; LWM =
51%) compared with the HMR. Additional food was requested
earlier after the HMR than the LMR (3.1 vs 3.9 hours,
respectively), although voluntary energy intake did
not differ. CONCLUSIONS: Differences in insulin response
between the meal replacements occurred, and prolongation
of satiety after the LMR, based on time to request additional
food, was observed. We speculate that the prolonged
satiety associated with low GI foods may prove an effective
method for reducing caloric intake and achieving long-term
weight control.
PMID: 12612226
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Departments of Nutrition.
The epidemiological data that
directly examine whole grain v. refined grain intake
in relation to weight gain are sparse. However, recently
reported studies offer insight into the potential role
that whole grains may play in body-weight regulation
due to the effects that the components of whole grains
have on hormonal factors, satiety and satiation. In
both s and observational studies the intake of whole-grain
foods was inversely associated with plasma biomarkers
of obesity, including insulin, C-peptide and leptin
concentrations. Whole-grain foods tend to have low glycaemic
index valuesresulting in lower postprandial glucose
responses and insulin demand. High insulin levels may
promote obesity by altering adipose tissue physiology
and by enhancing appetite. The fibre content of whole
grains may also affect the secretion of gut hormones,
independent of glycaemic response, that may act as satiety
factors. Future studies may examine whether whole grain
intake is directly related to body weight, and whether
the associations are primarily driven by components
of the grain, including dietary fibre, bran or germ.
PMID: 12740053
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Department of Medicine, Children's
Hospital, Boston, Massachusetts 02115, USA.
Prevalence rates of overweight
and obesity have risen precipitously in the United States
and other developed countries since the 1960s, despite
comprehensive public health efforts to combat this problem.
Although considerable attention has been focused on
decreasing dietary fat and increasing physical activity
level, the potential relevance of the dietary glycemic
index to obesity treatment has received comparatively
little scientific notice. This examines how the glycemic
and insulinemic responses to diet may affect body weight
regulation, and argues for the potential utility of
low glycemic index diets in the prevention and treatment
of obesity and related complications.
PMID: 12733742
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Faculty of Medicine, Human Nutrition
Center, University of Chile, PO Box, Correo 21, Santiago,
Chile.
A study was performed to examine
the rate of digestion of available carbohydrate in legumes
and its mixtures with cereals, prepared as commonly
eaten. The legumes and cereals studied were lentil (Lens
sculenta), pea (Pisum sativum)bean (Phaseolus vulgaris,
var tortola), rice (Oryza sativa) and spaghetti. Foods
were purchased at the city market. Total starch content
and the carbohydrate digestion rates were determined
using the enzymatic method proposed by Englyst et al.
Total starch levels ranged from 7.78 g/100 g in cooked
flour bean to 20.6 g/100 g in a bean-spaghetti dish,
and dietary fiber contents ranged from 2.4 g/100 g in
a cooked 70:30 lentil-rice mixture to 5.26 g/100 g in
a cooked whole bean. The rapid digestion rate carbohydrates
showed values from 4.8 in the bean soup to 8.9 in the
bean-spaghetti combination. The same results show, expressed
as rapid available glucose (RAG), the amount of rapid
carbohydrate/100 g food or meal as eaten, and as the
starch digestion index (SDI), the percentage of rapid
carbohydrate digestion rate in relation to the total
amount of carbohydrate. The RAG values ranged between
5.0 for cooked beans and 10 for cooked beans and spaghetti,
and the SDI ranged between 40 for cooked pea flour and
62 for cooked bean flour. Legumes prepared as soup showed
a higher rapid digestion rate than legumes prepared
as whole grain. The bean-spaghetti based-meal and the
lentil-based meal showed glycemic index mean and standard
deviation values of 76.8 +/- 43.4 and 49.3 +/- 29.5,
RAG values of 7.0 and 6.0, and SDI values of 57 and
54, respectively. The knowledge of the importance of
the carbohydrate digestion rates in human health in
increasing, and probably will soon be used in the development
of the food pyramid. The foods with a moderate fraction
of rapid digestion rate, such as legumes, should be
included in the base of the pyramid.
PMID: 12701368
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Department of Nutritional Sciences,
Faculty of Medicine, University of Toronto, Toronto,
Ontario, Canada.
Current dietary guidelines of
the American Diabetes Association emphasize the importance
of minimizing risk factors for cardiovascular disease
while maximizing diabetes control. Potential advantages
are seen for increased monounsaturated fat intake, but
only the quantity rather than the quality of the carbohydrate
is considered important. However, of the carbohydrate
issue suggests that many cultures now at high risk of
diabetes originally consumed starchy staples higher
in fiber and with a lower glycemic index than eaten
currently. Furthermore, diets high in cereal fiber have
been associated with improved glycemic control, and
low glycemic index diets resulted in reduction in glycosylated
proteins in type 1 and 2 diabetes. Finally, large cohort
studies have demonstrated beneficial effects of cereal
fiber and low glycemic index carbohydrate foods in reducing
the risk both for diabetes and cardiovascular disease.
The effect of insoluble cereal fiber is not readily
explained, but a low glycemic index may result from
a slower rate of carbohydrate absorption. Increased
meal frequency as a model for reducing the rate of carbohydrate
absorption has been shown to reduce day-long glucose
and insulin levels in type 2 diabetes and reduce serum
lipids in nondiabetic subjects. Therefore, there appears
to be a potential role for low glycemic index, high-cereal
fiber foods for prevention and treatment of diabetes.
Both the nature of the dietary fat and the carbohydrate
should be considered as potentially modifiable factors
that together with weight control and exercise may play
a role in diabetes and cardiovascular disease prevention
and treatment.
PMID: 12566136
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URPOI & UFDNH, National Institute
for Agronomic Research (INRA), Rue de la Geraudiere,
BP 71627, 44316 Nantes Cedex, 03, France.
Starch and fibre can be extracted,
using wet or dry processes, from a variety of grain
legumes and used as ingredients for food. alpha-Galactosides
can be isolated during wet processes from the soluble
extract. Starch isolates or concentrates are mostly
produced from peas, whereas dietary fibre fractions
from peas and soyabean are commercially available. The
physico-chemical characteristics of fibre fractions
very much depend on their origin, outer fibres being
very cellulosic whereas inner fibres contain a majority
of pectic substances. Inner fibres are often used as
texturing agents whereas outer fibres find their main
uses in bakery and extruded products, where they can
be introduced to increase the fibre content of the food.
Most investigations on impacts on health have been performed
on soyabean fibres. When positive observations were
made on lipaemia, glucose tolerance or faecal excretion,
they were unfortunately often obtained after non-realistic
daily doses of fibres. Legume starches contain a higher
amount of amylose than most cereal or tuber starches.
This confers these starches a lower bioavailability
than that of most starches, when raw or retrograded.
Their low glycaemic index can be considered as beneficial
for health and especially for the prevention of diseases
related to insulin resistance. When partly retrograded,
these starches can provide significant amount of butyrate
to the colonic epithelium and may help in colon cancer
prevention. alpha-Galactosides are usually considered
as responsible for flatus but their apparent prebiotic
effects may be an opportunity to valorize these oligosaccharides.
PMID: 12498630
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The Hebrew University of Jerusalem,
Faculty of Agricultural, Food and Environmental Quality
Sciences, Institute of Biochemistry, Food Science and
Nutrition, P.O. Box 12, Rehovot, 76100, Israel.
This evaluates the potential health
benefits of three legume sources that rarely appear
in Western diets and are often overlooked as functional
foods. Fenugreek (Trigonella foenum graecum) and isolated
fenugreek fractions have been shown to act as hypoglycaemic
and hypocholesterolaemic agents in both animal and human
studies. The unique dietary fibre composition and high
saponin content in fenugreek appears to be responsible
for these therapeutic properties. Faba beans (Vicia
faba) have lipid-lowering effects and may also be a
good source of antioxidants and chemopreventive factors.
Mung beans (Phaseolus aureus, Vigna radiatus) are thought
to be beneficial as an antidiabetic, low glycaemic index
food, rich in antioxidants. Evidence suggests that these
three novel sources of legumes may provide health benefits
when included in the daily diet.
PMID: 12498629
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Department of Psychology, University
of Wales Swansea, Singleton Park, Swansea, SA2 8PP UK.
RATIONALE: Glucose is the main
metabolic fuel of the brain. The rate of glucose delivery
from food to the bloodstream depends on the nature of
carbohydrates in the diet, which can be summarized as
the glycaemic index (GI). OBJECTIVES: To assess the
benefit of a low versus high GI breakfast on cognitive
performances within the following 4 h. METHODS: The
influence of the GI of the breakfast on verbal memory
of young adults was measured throughout the morning
in parallel to the assessment of blood glucose levels.
The learning abilities of rats performing an operant-conditioning
test 3 h after a breakfast-like meal of various GI was
also examined. RESULTS: A low GI rather than high GI
diet improved memory in humans, especially in the late
morning (150 and 210 min after breakfast). Similarly,
rats displayed better learning performance 180 min after
they were fed with a low rather than high GI diet. CONCLUSION:
Although performances appeared to be only remotely related
to blood glucose, our data provide evidence that a low
GI breakfast allows better cognitive performances later
in the morning.
PMID: 12488949
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Research Department of Human Nutrition,
Centre for Advanced Food Studies, The Royal Veterinary
and Agricultural University, Frederiksberg, Denmark.
In diabetes research the glycaemic
index (GI) of carbohydrates has long been recognized
and a low GI is recommended. The same is now often the
case in lipid research. Recently, a new debate has arisen
around whether a low-GI diet should also be advocated
for appetite- and long-term body weight control. A systematic
was performed of published human intervention studies
comparing the effects of high- and low-GI foods or diets
on appetite, food intake, energy expenditure and body
weight. In a total of 31 short-term studies (< 1 d),
low-GI foods were associated with greater satiety or
reduced hunger in 15 studies, whereas reduced satiety
or no differences were seen in 16 other studies. Low-GI
foods reduced ad libitum food intake in seven studies,
but not in eight other studies. In 20 longer-term studies
(< 6 months), a weight loss on a low-GI diet was seen
in four and on a high-GI diet in two, with no difference
recorded in 14. The average weight loss was 1.5 kg on
a low-GI diet and 1.6 kg on a high-GI diet. To conclude,
there is no evidence at present that low-GI foods are
superior to high-GI foods in regard to long-term body
weight control. However, the ideal long-term study where
ad libitum intake and fluctuations in body weight are
permitted, and the diets are similar in all aspects
except GI, has not yet been performed.
PMID: 12458971
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Department of Medicine, Children's
Hospital, Boston, MA 02115, USA.
A reduction in dietary fat has
been widely advocated for the prevention and treatment
of obesity and related complications. However, the efficacy
of low-fat diets has been questioned in recent years.
One potential adverse effect of reduced dietary fat
is a compensatory increase in the consumption of high
glycaemic index (GI) carbohydrate, principally refined
starchy foods and concentrated sugar. Such foods can
be rapidly digested or transformed into glucose, causing
a large increase in post-prandial blood glucose and
insulin. Short-term feeding studies have generally found
an inverse association between GI and satiety. Medium-term
s have found less weight loss on high GI or high glycaemic
load diets compared to low GI or low glycaemic load
diets. Epidemiological analyses link GI to multiple
cardiovascular disease risk factors and to the development
of cardiovascular disease and type 2 diabetes. Physiologically
orientated studies in humans and animal models provide
support for a role of GI in disease prevention and treatment.
This examines the mechanisms underlying the potential
benefits of a low GI diet, and whether such diets should
be recommended in the clinical setting.
PMID: 12458970
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Food Industry Science Centre, New
Zealand Institute for Crop and Food Research, Palmerston
North.
The glycaemic index (GI) is the
blood glucose response to carbohydrate in a food as
a percentage of the response to an equal weight of glucose.
Because GI is a percentage, it is not related quantitatively
to food intakes, and because it is based on equi-carbohydrate
comparisons, GI-based exchanges for control of glycaemia
should be restricted to foods providing equal carbohydrate
doses. To overcome these limitations of GI, the glycaemic
glucose equivalent (GGE), the weight of glucose having
the same glycaemic impact as a given weight of food,
is proposed as a practical measure of relative glycaemic
impact. To illustrate the differences between GGE and
GI in quantitative management of postprandial glycaemia,
published values for carbohydrate content, GI and serving
size of foods in the food groupings, breads, breakfast
cereals, pulses, fruit and vegetables, were used to
determine the GGE content per equal weight and per serving
of foods. Food rankings and classifications for exchanges
based on GGE content were compared with those based
on GI. In all of the food groupings analysed, values
for relative glycaemic impact (as GGE per 100 g food
and per serving) within each of the categories, low,
medium and high GI were too scattered for GI to be a
reliable indicator of the glycaemic impact of any given
food. Correlations between GI and GGE content per serving
were highest in food groupings of similar carbohydrate
content and serving size, including breads (r = 0.73)
and breakfast cereals (r = 0.8), but low in more varied
groups including pulses (r = 0.66), fruit (r = 0.48)
and vegetables (r = 0.28). Because of the non-correspondence
of GI and GGE content, food rankings by GI did not agree
with rankings by GGE content, and placement of foods
in GI-based food exchange categories was often not appropriate
for managing glycaemia. Effects of meal composition
and food intake on relative glycaemic impact could be
represented by GGE content, but not by GI. Because GGE
is not restricted to equicarbohydrate comparisons, and
is a function of food quantity, GGE may be applied,
irrespective of food or meal composition and weight,
and in a number of approaches to the management of glycaemia.
Accurate control of postprandial glycaemia should therefore
be achievable using GGE because they address the need
to combine GI with carbohydrate dose in diets of varying
composition and intake, to obtain a realistic indication
of relative glycaemic impact.
PMID: 12230236
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School of Allied Medical Professions-Medical
Dietetics Division, The Ohio State University, Columbus,
OH 43210-1234, USA.
The study objective was to determine
whether a small dose of fructose administered before
or simultaneously with a high glycemic index, starchy
food decreases postprandial glycemic response. Nondiabetic
healthy adults (n = 31; mean +/- SEM: age, 26 +/- 1
y; weight, 66.1 +/- 2.6 kg; body mass index, 23.3 +/-
0.6 kg/m(2)) were studied in a randomized crossover
design. Treatments consisted of 50 g available carbohydrate
from instant mashed potatoes fed alone (control) or
with 10 g fructose fed 60, 30 or 0 min before the potato
meal. Capillary finger-stick blood samples were analyzed
for glucose concentration at -60, -30, 0, 15, 30, 45,
60, 90 and 120 min relative to the ingestion of the
potato meal. Compared with the control, the positive
incremental area under the glucose curve was reduced
25 and 27% (P < 0.01) when fructose was fed either 60
or 30 min before the meal, respectively. In contrast
to previous studies demonstrating that immediate administration
of a small amount of fructose lowers the glycemic response
to a glucose solution, we found that fructose must be
consumed before a starchy food to reduce postprandial
glycemia.
PMID: 12221216
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Unita di epidemiologia, Istituto
nazionale per lo studio e la cura dei tumori, via Venezian
1, 20133 Milano.
Alzheimer Disease, characterised
by a global impairment of cognitive functions, is more
and more common in Western societies, both because of
longer life expectancy and, probably, because of increasing
incidence. Several hints suggest that this degenerative
disease is linked to western diet, characterised by
excessive dietary intake of sugar, refined carbohydrates
(with high glycaemic index), and animal product (with
high content of saturated fats), and decreased intake
of unrefined seeds--cereals, legumes, and oleaginous
seeds--and other vegetables (with high content of fibres,
vitamins, polyphenols and other antioxidant substances,
phytoestrogens) and, in several populations, of sea
food (rich in n-3 fatty acids). It has been hypothesised,
in fact, that AD, may be promoted by insulin resistance,
decreased endothelial production of nitric oxide, free
radical excess, inflammatory metabolites, homocysteine,
and oestrogen deficiency. AD, therefore, could theoretically
be prevented (or delayed) by relatively simple dietary
measures aimed at increasing insulin sensitivity (trough
reduction of refined sugars and saturated fats from
meat and dairy products), the ratio between n-3 and
n-6 fatty acids (e.g. from fish and respectively seed
oils), antioxidant vitamins, folic acid, vitamin B6,
phytoestrogens (vegetables, whole cereals, and legumes,
including soy products), vitamin B12 (bivalve molluscs,
liver), and Cr, K, Mg, and Si salts. This comprehensive
improvement of diet would fit with all the mechanistic
hypotheses cited above. Several studies, on the contrary,
are presently exploring monofactorial preventive strategies
with specific vitamin supplementation or hormonal drugs,
without, however, appreciable results.
PMID: 12197047
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Department of Nutritional Sciences,
Faculty of Medicine, University of Toronto, FitzGerald
Building, 150 College Street, Toronto, Ontario, Canada
M5S 3E2.
Increased satiety and decreased
food intake are reported following the consumption of
low glycaemic index (GI) foods, which gradually increase
blood glucose. This observation, however, is not uniformly
supported and few studies have examined the impact of
different GI foods on satiety and intake in the elderly.
After an overnight fast, 10 men and 10 women (aged 60-82
years) consumed similar amounts of available carbohydrate
as high (glucose drink or potatoes) or low (barley)
GI foods or a non-energy placebo drink on four mornings.
Blood glucose and subjective appetite were measured
throughout a 120 min post-ingestion period, followed
by consumption of an ad libitum lunch. Differences in
plasma glucose after test food ingestion (glucose >
potatoes > barley > placebo; P < 0.03) did not predict
subjective appetite or lunch intake. Potatoes increased
subjective satiety the most, followed by barley, then
glucose, which trended towards greater satiety than
placebo. Potatoes led to less hunger than placebo (P
= 0.0023) and less prospective consumption than the
other three foods (P < 0.0083), and potatoes and barley
led to greater fullness than glucose and placebo (P
< 0.0001). Lunch intake was decreased, compared with
placebo (502 +/- 47 kcal, P < 0.031), by potatoes (405
+/- 40 kcal) and barley (441 +/- 41 kcal); however,
only potatoes (41.9 +/- 12.3%) led to greater compensation
at lunch for test food ingestion compared with glucose
(11.9 +/- 9.5%, P = 0.016). These results suggest that
elderly subjects are sensitive to the effects of different
foods on subjective appetite and food intake, and that
the GI of the foods tested did not predict their effects
on satiety and food intake.
PMID: 12090026
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Obesity Research Center, St. Luke's-Roosevelt
Hospital Center, Columbia University College of Physicians
and Surgeons, New York, NY 10025, USA.
It has been suggested that foods
with a high glycemic index are detrimental to health
and that healthy people should be told to avoid these
foods. This paper takes the position that not enough
valid scientific data are available to launch a public
health campaign to disseminate such a recommendation.
This paper explores the glycemic index and its validity
and discusses the effect of postprandial glucose and
insulin responses on food intake, obesity, type 1 diabetes,
and cardiovascular disease. Presented herein are the
reasons why it is premature to recommend that the general
population avoid foods with a high glycemic index.
PMID: 12081854
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Human Nutrition Unit, School of
Molecular and Microbial Biosciences, University of Sydney,
NSW, Australia.
Although weight loss can be achieved
by any means of energy restriction, current dietary
guidelines have not prevented weight regain or population-level
increases in obesity and overweight. Many high-carbohydrate,
low-fat diets may be counterproductive to weight control
because they markedly increase postprandial hyperglycemia
and hyperinsulinemia. Many high-carbohydrate foods common
to Western diets produce a high glycemic response [high-glycemic-index
(GI) foods], promoting postprandial carbohydrate oxidation
at the expense of fat oxidation, thus altering fuel
partitioning in a way that may be conducive to body
fat gain. In contrast, diets based on low-fat foods
that produce a low glycemic response (low-GI foods)
may enhance weight control because they promote satiety,
minimize postprandial insulin secretion, and maintain
insulin sensitivity. This hypothesis is supported by
several intervention studies in humans in which energy-restricted
diets based on low-GI foods produced greater weight
loss than did equivalent diets based on high-GI foods.
Long-term studies in animal models have also shown that
diets based on high-GI starches promote weight gain,
visceral adiposity, and higher concentrations of lipogenic
enzymes than do isoenergetic, macronutrientcontrolled,
low-GI-starch diets. In a study of healthy pregnant
women, a high-GI diet was associated with greater weight
at term than was a nutrient-balanced, low-GI diet. In
a study of diet and complications of type 1 diabetes,
the GI of the overall diet was an independent predictor
of waist circumference in men. These findings provide
the scientific rationale to justify randomized, controlled,
multicenter intervention studies comparing the effects
of conventional and low-GI diets on weight control.
PMID: 12081852
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Human Nutrition Unit, School of
Molecular and Microbial Biosciences, University of Sydney,
NSW, Australia.
Reliable tables of glycemic index
(GI) compiled from the scientific literature are instrumental
in improving the quality of research examining the relation
between GI, glycemic load, and health. The GI has proven
to be a more useful nutritional concept than is the
chemical classification of carbohydrate (as simple or
complex, as sugars or starches, or as available or unavailable),
permitting new insights into the relation between the
physiologic effects of carbohydrate-rich f
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