|
|
| |
|
| |
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.
|
|
|
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
|
|
|
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
|
|
|
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
|
|
|
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
|
|
|
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
|
|
|
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
|
|
|
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
|
|
|
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
|
|
|
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
|
|
|
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
|
|
|
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
|
|
|
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
|
|
|
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
|
|
|
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
|
|
|
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
|
|
|
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
|
|
|
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
|
|
|
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
|
|
|
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
|
|
|
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
|
|
|
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
|
|
|
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
|
|
|
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
foods and health. Several prospective observational studies
have shown that the chronic consumption of a diet with a high
glycemic load (GI x dietary carbohydrate content) is independently
associated with an increased risk of developing type 2 diabetes,
cardiovascular disease, and certain cancers. This revised
table contains almost 3 times the number of foods listed in
the original table (first published in this Journal in 1995)
and contains nearly 1300 data entries derived from published
and unpublished verified sources, representing > 750 different
types of foods tested with the use of standard methods. The
revised table also lists the glycemic load associated with
the consumption of specified serving sizes of different foods.
PMID: 12081815
|
|
|
Institute of Nutrition and Food Hygiene,
Chinese Academy of Preventive Medicine, Beijing 100050, China.
In order to study the effect of protein,
fat and dietary fiber on glycemic index(GI) of mixed food,
the response of blood glucose and plasma insulin to nine diets
with different components of food were tested by using glucose
oxidase and radioimmunoassay. Glycemic index of 9 mixed foods
show as follows, rice: 83.2 +/- 3.1, rice + stir fry pork:
72.0 +/- 14.0, rice + stir fry pork and celery: 57.1 +/- 11.2,
rice + stir fry garlic sprout: 57.9 +/- 7.8, rice + stir fry
garlic sprout and eggs: 62.8 +/- 16.7, steamed bread: 80.1
+/- 22.5, steamed bread + butter: 68.0 +/- 16.3, and steamed
bread + beef: 49.4 +/- 22.8. Protein(P, beta 1 = -0.696, P
< 0.01) and dietary fiber(Fi, beta 2 = -7.364, P < 0.01) can
reduce the blood glucose response and were significantly related
to GI. Fat also can inhibit the increment of blood glucose,
but there is no significant relation with GI. When the co-ingestion
of protein with carbohydrate, the serum insulin response increased
greatly and the glycemic response reduced. The addition of
fat can reduce the glycemic response without change in serum
insulin. Dietary fiber can reduce the serum insulin response
and inhibit the glycemic response. CONCLUSION: Protein and
dietary fiber of mixed food could markedly affect the glycemic
index of foods and reduced the blood glucose response.
PMID: 12016989
|
|
|
Jean Mayer USDA Human Nutrition Research
Center on Aging at Tufts University, Boston, Massachusetts
02111, USA.
We evidence regarding the influence
of dietary fat, fiber, the glycemic index and sugar on energy
intake and body weight. Although data from comprehensive long-term
studies are lacking, published investigations suggest that
the previous focus on lowering dietary fat as a means for
promoting negative energy balance has led to an underestimation
of the potential role of dietary composition in promoting
reductions in energy intake and weight loss. More randomized
s are needed to examine the relative utility of different
putative dietary factors in the treatment of obesity.
PMID: 11999542
|
|
|
University Complutense Madrid, Faculty
of Pharmacy, Department of Nutrition, Avda. Complutense s/n
Ciudad University, E-28040 Madrid, Spain.
The capacity of two species of edible
seaweeds (Wakame, Undaria pinnatifida and Chondrus, Chondrus
crispus) to modify the rate of white bread starch digestibility
by an in vitro digestion system, as well as glucose retardation
index and apparent viscosity were studied. Both Algae showed
different effect on glucose retardation index. While Wakame
did not make difficult dialysis of glucose, it only retained
2.50 +/- 2.99% to respect a negative control. Chondrus impaired
the diffusion of a 28.70 +/- 2.35% of glucose, which are very
close to those of citrus pectin (31.50 +/- 4.12%). On the
other hand, viscosity of Chondrus solution was higher than
Wakame and slightly lower than citrus pectin solution. The
analysis showed a very low content of total starch in Wakame
(0.51%) and Chondrus (0.47%). Algae reduced the digestion
of white bread starch. The profile of starch hydrolysis was
characteristic for each alga. Glycaemic index estimated from
the degree of starch hydrolysis within 90 min was low (79)
with respect to white bread (value 100). Seaweeds showed a
suitable capacity to modify in vitro starch digestibility
of white bread. Chondrus produces a more pronounced response.
This fact seem to be due to different composition of samples.
PMID: 11890047
|
|
|
Instituto de Medicina Social, State University
of Rio de Janeiro, UERJ, Brazil.
OBJECTIVE: To evaluate the dietary patterns
of adults living in the city of Rio de Janeiro, Brazil and
their associations with body mass index (BMI). RESEARCH METHODS
AND PROCEDURES: A survey was conducted in 1996 in a probabilistic
sample of 2040 households. Weight and height were measured
and food intake was based on an 80-item semi-quantitative
food frequency questionnaire. Dietary patterns were identified
through factor analysis. RESULTS: More than one-third of the
adult population (20 to 60 years old) was overweight (BMI
= 25 to 29.9 kg/m(2)), and 12% were obese (BMI >or= 30 kg/m(2)).
Three major dietary patterns were identified: mixed pattern
when all food groups and items had about the same factor loading,
except for rice and beans; one pattern that relies mainly
on rice and beans, which was called a traditional diet; and
a third pattern, termed a Western diet, where fat (butter
and margarine) and added sugar (sodas) showed the highest
positive loading and rice and beans were strong negative components.
Among men, the Western diet also included deep-fried snacks
and milk products with high positive values. The traditional
diet was associated with lower risk of overweight/obesity
in logistic models adjusted for dieting, age, leisure physical
activity, and occupation (13% reduction in men and 14% reduction
in women comparing the traditional and Western diets). DISCUSSION:
Factors contributing to the effects of the Brazilian traditional
diet may include low-energy density, high-dietary fiber content,
incorporation of low glycemic index foods such as beans, or
a relatively low food variety.
PMID: 11786600
|
|
|
| |
