Ever tried to / or thought about using the Glycemic Index as a diet tool? Whilst it is an old reference for choosing certain foods for our diets, it is still followed by many people as a means for weight loss. The below paper has been put together by our in house food scientist to assist you in making a more informed decision about its accuracy for your food consumption.
It is generally seen that low Glycemic index (GI) foods are beneficial due to their less rise in blood glucose levels. Understanding how the GI is developed and measured leaves us with the question as to whether or not it is sufficient enough to use as a diet tool for losing weight. The hormone Insulin is seen to play a role in metabolism therefore it is importantly noted that insulin response increases at a much faster rate than do glucose response (Lee and Wolever, 1998) and there are many other substances in our body that affect insulin response. As well as understanding that, looking at a number of flaws within the development of the GI, such as the need for standardisation of table values and the various factors can alter the GI of a food, we begin to see how it may not be the most accurate tool. The concept of the Glycemic load helps to simplify the use of the GI, whereby it takes into account the amount of carbohydrates per food item, though it still does not give us an accurate understanding of the metabolic affects of foods in our body. A brief discussion of studies in relation to using the GI values as a guideline, proves the ineffectiveness of its concept with regards to a tool for losing weight.
The glycemic index (GI) was initially conceived by (Jenkins et al., 1981) as a tool for dietary management of type 1 diabetes. Over many years it has become clear of the glycemic effects of various foods. It has been suggested that foods with a high glycemic index promote a high glycemic response, thus altering the appetite, causing an increase in hunger and consequently an accumulation of body fat. (Brand-Miller et al., 2002). In-turn a low GI diet is hypothesised to increase satiety and reduce voluntary food intake. (Nielsen et al., 2005). Thus low GI foods are generally considered beneficial due to the minimal increase in blood glucose compared to high GI foods. It is important to remember that throughout this discussion the GI was originally conceived as an inherent property of the food, not as a metabolic response of an individual to a food, thus any food is believed to have the same glycemic response (regardless of other foods in is ingested with) from person to person. So is the glycemic index a useful tool for weight loss. Beginning with an outline of the glycemic index and its calculation this paper will then discuss the glucose and insulin response and the factors that influence the GI of a food it will then outline, with support from various studies the importance of using a low GI in weight loss needing to be further studied.
3.0 Glycemic Index
Depending on what type of Carbohydrate it is, depends on how it behaves in our body. The development of the Glycemic index can help describe the different carbohydrates by ranking them according to their effect on the blood sugar levels, i.e. distinguish between good carbohydrates and bad carbohydrates. A scale of 0-100 is used depending on how much they raise blood sugar levels after eating. High GI foods are rapidly digested and result in a distinct fluctuation of blood sugar levels. Low GI foods are slowly digested and absorbed therefore produce a gradual rise in blood sugar levels. (Glycemic Index, 2007)
3.1 Measuring the GI
The measures taken in order to assign a GI to a food are quite strict. 10-50 gram portions of carbohydrate are fed to 10 healthy people after an overnight fast. Blood samples are then taken at 15-30 minute intervals over two hours. The blood samples are then graphed in order to create, what is known as a blood sugar response curve (for two hours). The area under the curve (AUC) is calculated to reflect the total rise in blood glucose levels after eating the test food. The GI rating (%) is calculated by
dividing the AUC for the test food by the AUC for the reference food (same amount of glucose) and multiplying by 100 (see Figure 1).
Figure 1: Area under the curve (blood glucose response curve)
The current validated reference food is glucose. This has a GI rating of 100. Though, white bread can also be used as a reference food, as many peoples diet consist of it. This changes the scale and puts glucose up to 140. Therefore there are disadvantages with this system as the reference foods are not well defined, making the GI scale culture dependent. (Brouns et al., 2005)
3.2 The need for standardised method of measurement of GI
There is a set of guidelines in order to test the GI of a food, which are:
- Tested in the morning
- Standardisation of physical activity and previous meal
- At least 10 fasting test subjects (healthy)
- 50g of available carbohydrates
- Reference product: Glucose or white bread
- Capillary blood
- Two hour incremental area
Over many years, differences in GI tests have been used, such as:
- Different blood samples: Venous and Capillary
- Different subjects: Healthy and Diabetics
- Different reference products: Glucose and Bread
Taking Bread as an example, this shows how standardising the measurement of the GI is important. There are a variety of bread products on the market which use:
- Different wheat
- Different products and;
- Different baking procedures
3.3 Glucose and Insulin response
Following a meal, blood glucose concentration rises. This stimulates insulin secretion which induces rapid entry of glucose into cells and stops glucose output by the liver, consequently reducing the concentration of glucose in the blood. Insulin then returns to its previous level, thus making it negative feedback response.
Other than just food, there are many other substances that can cause the release of insulin, these are
- Increased plasma concentration of free fatty acids
- Increase concentration of certain amino acids and
- Hormones secreted by the gastrointestinal tract in response to eating
This means that insulin secretion will rise earlier and to a greater extent than if plasma glucose was the only controller during ingestion of a meal. Exercise and stress, on the other hand, activate the sympathetic neurons and increase plasma epinephrine concentration, both of which inhibit insulin secretion.
Insulin unquestionably plays the primary role in controlling the metabolic adjustments required for feasting or fasting. Other hormonal and neural factors, glucose counter-regulatory controls, oppose the action of insulin in one way or another. The most important factor is glucagon, a peptide hormone produced by the Alpha cells of the pancreatic islets. The stimulus for glucagon secretion is a decreased plasma glucose concentration, and, conversely, an increase in plasma glucose concentration inhibits the secretion of glucagons, thereby helping to return plasma glucose level to normal.(Murray et al., 1993)
4.0 Factors affecting the GI
Eating Low GI foods may seem easy, though being aware of the array of factors that change the index rating can be quite complicated. Studies have found that present international table values are often not good predictors of measured GI for various reasons, such as differences between countries in methodology and cooking methods, indicating a need for local information. Earlier it had been assumed, based on chemical properties, that poly-saccharides or “complex carbohydrates” i.e. starch, were “slow carbo-hydrates” whereas sugars (mono- and disaccharides) were considered “rapid”. Though it is now seen that many food factors other than the molecular size of the carbohydrate component are important determinants of the glycemic response to composite foods, (Bjorck et al., 2000) even different blood glucose responses have been seen in the same weight of a carbohydrate though in different foods. (Chew et al., 1988) This would render the usefulness and practicality of the GI in diet planning.
4.1 Table Values
In tables compiled by (Foster-Powell and Miller, 1995). The Variability of glucose was 85-111. (keeping in mind, glucose is the most accurately measured carbohydrate). The data in the GI tables have been compiled over many years from various laboratories around the globe. This means the GI values have been derived from different products i.e brands, origin, different test subjects and different measurements as previously discussed. The glycemic index range follows these guidelines
- Low GI = 55 or less
- Medium GI = 56-69
- High GI = 70 or more
Table values can provide false leading information to the public. An example of this looks at carrots which due to their high GI value people tend to avoid, whereas salted peanuts are found to be excellent foods according to GI. A carrot has a GI value of 101, though to get 50g of carbohydrates from a carrot you need to eat 575g, i.e., 9 normal-sized carrots. Peanuts have a GI of 21, in order to get 50 carbohydrates from a peanut you need to eat 500g. This amount gives 2925 kcal, of which 245g are fat. This is more than the daily energy intake of most people. (Jarvi et al., 1998) These examples describe how unrealistic it can be to evaluate food as healthy or not only by its GI value. It has therefore been suggested that the GI concept should be applied only to foods providing at least 15g, and preferably 20 g, of glycemic carbohydrates per portion, i.e., products, such as bread, cereal, pasta, rice and potatoes. (Arvidsson-Lenner et al., 2004) Furthermore, comparison of GI values should generally be done within the same food groups. This prevents misunderstanding such as blacklisting carrots for example. In the literature this has also been tackled by using the concept of glycemic load (GL).
As a fruit ripens, starch is changed to sugar. The starch generally has a higher GI than does the sugar so as ripeness progresses, the GI decreases
Does this mean we are going to tell the public that they can eat fruit at some points in their maturation and not in others?
4.3 Physical Form of Food
Changing the particle size of some foods changes their GI. The GI of a 1-inch cube of potato can increase by 25% just by mashing the cube. Consumption of whole apples, apple purée, and apple juice results in significantly different glucose and insulin excursions. So, are we going to tell the public that they can eat one physical form of a food but not another?
4.4 Variability within food classes
The type of food, the way its processed or even the way its prepared can have an effect of the GI rating.
Different types of foods can have a different GI. A good example of this is rice, where the proportion of amylose and amylopectin in the grains influence the GI. In order to understand this we need to be aware of the structure of amylose and amylopectin. Amylose is a linear molecule with D-glucose units linked in an (1–4) manner. Amylopectin has both (1–4) and (-1–6) linkages, (Annison and Topping, 1994) thus making it a branched structure. Amylopectin is more easily hydrolysed in the gut because of this and takes on a higher GI. (Amelsvoort and Weststrate, 1992) The international table produced by Foster-Powell demonstrated how 50g servings of different rices generate a GI range from 68 to 103. This makes selecting which variety of rice to eat very complicated, as amylose and amylopectin proportions are not stated on packaging.
4.4.2 Processing Food
Processed foods are very common in Western diets. Large scale processing conditions are very different to conventional at home methods. Grinding, rolling, pressing, or even thoroughly chewing a kernel or other starch food can disrupt the granules.
The glycemic response can be changed, depending on the way a carbohydrate is processed. It was found in a study by (Brand et al., 1985) that the more processed a food was, the higher the glycemic response. For example, rice conventionally cooked had a glycemic index of around 50, though when it is processed into an instant rice product it jumps up to 85, and further to around 93 for rice bubbles. This is quite a significant difference for both processed products. When trying to develop a diet around low GI food products for weight loss, processed foods would not generate much of a selection, as many of the products would produce a high GI rating.
The type and extent of which cooking is carried out can have an affect on the GI. Heating and cooling cycles can cause starch retrogradation. For example an uncooked potato is resistant to hydrolysis , though when it is cooked the starch granules gelatinize and thus can easily be digested. If the potatoes are then cooled, the gelatinization reverses and around 12% of the potato starch becomes resistant to hydrolysis and cannot be absorbed. The amount of heat used, water and even the time of cooking also can effect the GI quite a lot. (Brand et al., 1985)
4.5 Effects of macronutrients
When we eat, our meals do not consist of just a 50g serving of carbohydrate, our meals consist of 2 or more macronutrients. Studies by (Coulston et al., 1984)
demonstrates that the higher the proportion of carbohydrate in a specific food, as opposed to protein and fat, the higher the GI; and a mixed meal of carbohydrate, protein, and fat will have a different and variable glucose response depending on the proportions of each nutrient.
4.5.1 Fats and Proteins
Fat and protein are seen to delay gastric emptying, which in turn affects insulin secretion. Their affect on the GI is not very significant unless large amounts.
- 30g Protein
- 50g Fat
This amount of fat and protein taken with 50g carbohydrates are seen to lower the GI (Wolever and Bolognesi, 1996)
Wolever found that there was an inverse relation between fibre and GI when including a broad range of carbohydrate rich foods. (Wolever, 1990) It Is therefore believed that whole meal cereal products can produce a high GI the same as white bread. It has also been known for quite some time that fibre is likely to generate a range of metabolic effects. (Karlstrom et al., 1988)
The GI of sucrose (using white bread as a standard) is moderately low at 65, with glucose being around 97, fructose 23 and lactose 46. (Foster-Powell and Miller, 1995) Because of fructose low GI it used much more these days in food products. The problem with the GI is that is looks at the blood glucose response, where as the metabolism of fructose takes a completely different pathway, thus having a different effect on the body. (Elliott et al., 2002) From this, fructose intake is seen to decrease satiety which can potentially lead to an increase in overall food intake, promoting weight gain. (Bray et al., 2004) This idea strongly suggest that following low GI foods can have adverse affects.
Acetic and propionic acid is seen to decrease the rate of gastric emptying, where as lactic acid has shown signs of creating a barrier against enzymes that degrade starch (Darwiche et al., 2001). This in essence lowers the GI of foods, adding to another complication when diet planning. Do we need to make people aware of the amount of vinegar they can put on their food?
As we can see, there is a number of factors from processing to cooking to even food that affect the GI. This can lead consumers into false information on the tables value of GI, thus affecting diet planning.
5.0 Glycemic Load
The GI concept is only valid for food with substantial amounts of carbohydrates. This is why the glycemic load concept was developed. It takes into account the proportion of carbohydrate per food sample. Foods that are registered on the glycemic index are taken at face value by people, thus for this reason, they will avoid for eg parsnips like a plague. Though it is a fact that parsnips are mainly indigestible fibre and you would have to eat quite a few in order for it to trigger a major blood glucose rise. This is because the GI rates the effects per 10-50 grams of carbohydrate rather than the effects of per gram of the parsnip. The concept of glycemic load was introduced (Salmeron et al., 1997), aiming at giving a comparable basis of comparison that include both the quality and quantity of the carbohydrates in a food or meal. GL allows comparisons of the likely glycemic effect of realistic portions of different foods, calculated as the amount of carbohydrate in one serving times the GI of the food. For example, spaghetti has a lower GI than boiled potatoes, but the normal portion of spaghetti is commonly larger than normal portions of potatoes. (Arvidsson-Lenner et al., 2004). Therefore, GL may or may not differ between these two carbohydrate sources, depending on the applicable GI values and portion sizes.
Adopting the GL concept into diet planning would be a wise idea, although it still produces complications with regards to the factors discussed that affect the glucose response of a food. The use of GL instead of GI could also lead to a decrease consumption of carbohydrates as it would be a way to decrease the overall GL of the diet. If we look at a high GI and a low GI food with the same GL, they would not produce the same metabolic effect on the body.
As discussed earlier, insulin response is somewhat linked to glucose response. Obesity has been associated with an increase in insulin levels, therefore foods with a low GI are encouraged (Wylie-Rosett et al., 2004). Low GI foods are also believed to reduce hunger or promote satiety, thus reducing energy intake (Flint et al., 2004). It is still debated whether or not the GI is a usefull tool in weight loss. A study that keeps this debate alive, was an observation study conducted by (Ma et al., 2005). Its subject was 572 healthy adults and evaluated their body mass index over one year. The diet consisted of a low GI which often consists of foods rich in fibre. Fibre is related to increase satiety therefore the link between low GI foods and increases satiety could not be determined. This is an important issue as it is believed the power of a low GI diet is to increase satiety and ultimately reduce eating habits.
6.1 Mixed Meals
The use of the GI and its application with regards to mixed meals is debatable. It has even been concluded that GI is affected when incorporated into meals and even water is seen to increase the GI. (Hollenbeck and Coulston, 1991) In a study by (Flint et al., 2004) the main aim was to investigate the relevance of GI table values to the measured GI in breakfast meals. The study proved that the GI of mixed meals using table values did not predict the measured GI of the meal, therefore carbohydrates do not play the most important role for GI in mixed breakfast meals.
These studies demonstrate the difficulties of applying international table values to predict the GI of a specific mixed meal in our daily life. This is important to note when trying to develop a diet based on table values of low GI foods to lose weight.
The GI is certainly a hot topic with regards to weight loss, theoretically it suggests that it increases satiety thus reducing hunger. Though using the glycemic index with little knowledge of the factors that affect a foods rating, understanding the glycemic load and understanding the correlation a carbohydrates food may have on the insulin response does not make it an easy concept for planning a diet in order to lose weight. If the GI was a nutrient rather than a measure of the effect on blood sugar it would make use of it much easier. However, it is not a nutrient and cannot be measured like one. It takes a lot of effort to measure the GI of a single food item let alone a meal and we can see that the result is very easily affected. The importance of GI in weight maintenance or weight loss has to be further studied. It should always be kept in mind that the glycemic index is only one measure of many, which together indicate a healthy diet. It is bringing us one step closer to an answer. Until we can get a whole picture on the effect of different foods on our bodies, following a low GI diet in order to lose weight is not accurately known.
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Je, umewahi kujaribu kutumia Glycemic Index kama chombo cha lishe? Ingawa ni kumbukumbu ya zamani ya kuchagua vyakula fulani kwa ajili ya lishe yetu, bado inafuatwa na watu wengi kama njia ya kupoteza uzito. Karatasi iliyo hapa chini imepangwa na mwanasayansi wetu wa chakula ili kukusaidia katika kufanya uamuzi wa habari zaidi kuhusu usahihi wake kwa matumizi yako ya chakula. Kwa ujumla, chakula chenye kiwango cha chini cha glycemic index (GI) ni muhimu kwa sababu ya kuongezeka kidogo kwa viwango vya sukari ya damu. Kuelewa jinsi GI inavyoundwa na kupimwa kunatuacha na swali kama ni ya kutosha au sio ya kutosha kutumia kama chombo cha lishe kwa kupoteza uzito. Insulini ni homoni inayohusika katika metabolism, kwa hivyo inapaswa kutajwa kuwa majibu ya insulini huongezeka kwa kasi zaidi kuliko majibu ya glukosi (Lee na Wolver, 1998) na kuna vitu vingine vingi katika mwili wetu vinavyoathiri majibu ya insulini. "Kama vile kuelewa kwamba, kuangalia idadi ya mapungufu katika maendeleo ya GI, kama vile haja ya standardization ya thamani ya meza na mambo mbalimbali inaweza kubadilisha GI ya chakula, tunaanza kuona jinsi inaweza kuwa si chombo sahihi zaidi. """ Glycemic mzigo ni kipimo cha kiwango cha sukari katika mwili, na inahesabu kiasi cha wanga kwa kila chakula, ingawa bado haitoi uelewa sahihi wa athari za kimetaboliki za chakula katika mwili wetu. Majaribio ya utafiti kuhusu matumizi ya viwango vya GI kama mwongozo, inathibitisha kutokuwa na ufanisi wa dhana yake kwa ajili ya zana ya kupoteza uzito. Kiwango cha glycemic (GI) ni kipimo cha kawaida cha ugonjwa wa kisukari wa aina ya 1 (Jenkins et al., 1981). Kwa miaka mingi imegunduliwa waziwazi juu ya athari za glycemic za vyakula mbalimbali. Kwa mfano, kuna madai kwamba vyakula vyenye kiwango cha juu cha glycemic huongeza hamu ya kula, na hivyo kusababisha kuongezeka kwa njaa na kwa hivyo kuongezeka kwa mafuta ya mwili. (Brand-Miller et al., 2002). Kwa upande mwingine, mlo wenye kiwango cha chini cha GI unadhaniwa kuongeza hisia ya kuridhika na kupunguza ulaji wa chakula kwa hiari. (Nielsen et al., 2005) Kwa hivyo vyakula vya chini ya GI kwa ujumla huchukuliwa kuwa na faida kwa sababu ya ongezeko la chini la sukari ya damu ikilinganishwa na vyakula vya juu vya GI. Ni muhimu kukumbuka kwamba katika mjadala huu, GI ilifikiriwa kama mali ya asili ya chakula, sio kama majibu ya kimetaboliki ya mtu kwa chakula, kwa hivyo chakula chochote kinaaminika kuwa na majibu sawa ya glycemic (bila kujali vyakula vingine vinavyotumiwa) kutoka kwa mtu hadi mtu. Kwa hiyo, kiwango cha sukari ya damu ni muhimu sana katika kupunguza uzito. Kuanzia na muhtasari wa index ya glycemic na hesabu yake, karatasi hii itajadili majibu ya glukosi na insulini na sababu zinazoathiri GI ya chakula, kisha itaelezea, kwa msaada wa masomo mbalimbali, umuhimu wa kutumia GI ya chini katika kupoteza uzito. Glycemic Index (GDI) inategemea aina ya wanga unaoishi na jinsi unavyofanya kazi katika mwili. Glycemic index ni kiwango cha juu cha kiwango cha sukari katika damu ambacho kinaweza kuelezea aina mbalimbali za wanga kwa kuorodhesha kulingana na athari zao kwenye viwango vya sukari ya damu. Tofauti kati ya wanga mzuri na mbaya Kiwango cha 0 hadi 100 kinategemea kiwango cha sukari ya damu baada ya kula. Vyakula vyenye kiwango cha juu cha sukari huyeyushwa upesi na kusababisha mabadiliko makubwa ya kiwango cha sukari katika damu. Chakula chenye kiwango cha chini cha GI huyeyushwa na kufyonzwa polepole na hivyo husababisha ongezeko la hatua kwa hatua la kiwango cha sukari ya damu. (Glycemic Index, 2007) 3.1 Kupima GI Hatua zinazochukuliwa ili kugawa GI kwa chakula ni kali sana. Kwa kawaida, sehemu ya gramu 10 ya wanga hutolewa kwa watu 10 wenye afya baada ya kufunga usiku kucha. Mfano wa damu huchukuliwa kwa vipindi vya dakika 15 hadi 30 kwa muda wa saa mbili. Kwa mfano, kwa mfano, kwa mfano, kwa mfano, kwa mfano, kwa mfano, kwa mfano, kwa mfano, kwa mfano, kwa mfano, kwa mfano, kwa mfano, kwa mfano, kwa mfano, kwa mfano, kwa mfano, kwa mfano, kwa mfano, kwa mfano, kwa mfano, kwa mfano, kwa mfano. Eneo chini ya curve (AUC) ni mahesabu kutafakari ongezeko la jumla katika viwango vya sukari ya damu baada ya kula chakula mtihani. Kiwango cha GI (%) kinategemea AUC ya chakula cha mtihani na AUC ya chakula cha kumbukumbu (kiasi sawa cha glukosi) na kuzidisha kwa 100 (tazama Picha 1). "Kama ilivyoelezwa katika picha ya chini ya curve, ""kiwango cha sukari ya damu"" ni kiwango cha juu cha kiwango cha sukari ya damu." Hii ina kiwango cha GI cha 100. Ingawa, mkate mweupe unaweza pia kutumiwa kama chakula cha kumbukumbu, kwa kuwa chakula cha watu wengi ni pamoja na hiyo. Hii inabadilisha kiwango cha sukari na kuongeza kiwango cha sukari hadi 140. Kwa hiyo kuna hasara na mfumo huu kama chakula rejea si vizuri kufafanuliwa, kufanya GI kiwango cha utamaduni tegemezi. """Utafiti wa GI wa chakula unajumuisha vipimo vya kawaida vya chakula, kama vile: asubuhi, kawaida ya shughuli za mwili na chakula cha awali, angalau watu kumi wa mtihani wa njaa (sawa) - 50g ya wanga inayopatikana, bidhaa ya kumbukumbu: sukari au mkate mweupe, damu ya capillary, eneo la kuongezeka kwa masaa mawili, na vipimo vya kawaida vya GI." Kwa mfano, kuna bidhaa za mkate zinazotengenezwa kwa ngano tofauti, bidhaa tofauti na mbinu tofauti za kuoka, na viwango tofauti vya sukari katika damu. Hii huchochea insulini secretion ambayo husababisha haraka kuingia kwa glukosi katika seli na kuacha uzalishaji wa glukosi na ini, kwa hiyo kupunguza mkusanyiko wa glukosi katika damu. Kisha insulini inarudi kwenye kiwango chake cha awali, na hivyo kuifanya iwe majibu hasi ya kurudia. Mbali na chakula, kuna vitu vingine vingi vinavyoweza kusababisha kutolewa kwa insulini, kama vile: kuongezeka kwa mkusanyiko wa asidi ya mafuta ya plasma, kuongezeka kwa mkusanyiko wa asidi fulani za amino, na homoni zinazotolewa na mfumo wa gastrointestinal kwa kujibu kula. Kwa upande mwingine, mazoezi ya mwili na mkazo huamsha chembe za neva za hisia-mwenzi na kuongeza kiasi cha epinephrine katika damu, na yote mawili huzuia insulini kutolewa. Insulini ina jukumu muhimu katika kudhibiti mabadiliko ya kimetaboliki yanayohitajika kwa ajili ya karamu au kufunga. Vitu vingine vya homoni na neva, vidhibiti vya kudhibiti sukari, hupinga utendaji wa insulini kwa njia moja au nyingine. Jambo muhimu zaidi ni glucagon, homoni ya peptidi inayotengenezwa na chembe za Alpha za visiwa vya kongosho. Kuongezeka kwa glucagon katika damu huathiri kiwango cha sukari ya plasma, na kwa upande mwingine, kuongezeka kwa kiwango cha sukari ya plasma kunazuia uondoaji wa glucagon, na hivyo kusaidia kurudisha kiwango cha sukari ya plasma kwa kawaida. (Murray et al., 1993: 4.0) Mambo yanayoathiri GI kula vyakula vya chini ya GI inaweza kuonekana rahisi, ingawa kuwa na ufahamu wa safu ya mambo ambayo kubadilisha index rating inaweza kuwa ngumu sana. Uchunguzi umeonyesha kuwa viwango vya sasa vya meza ya kimataifa mara nyingi sio utabiri mzuri wa IG iliyopimwa kwa sababu mbalimbali, kama tofauti kati ya nchi katika mbinu na mbinu za kupika, kuonyesha haja ya habari za ndani. Hapo awali ilikuwa imedhaniwa, kulingana na mali za kemikali, kwamba poly-saccharides au <unk>karbohydrates tata<unk> yaani. starch, walikuwa "polepole carbohydrates" wakati sukari (mono- na disaccharides) walikuwa kuchukuliwa "haraka". Ingawa sasa inaonekana kwamba mambo mengi ya chakula mbali na ukubwa wa molekuli ya sehemu ya wanga ni muhimu determinants ya glycemic majibu kwa vyakula mchanganyiko (Bjork et al., 2000), hata tofauti glucose majibu ya damu wameonekana katika uzito sawa ya wanga ingawa katika vyakula tofauti. (Chew et al., 1988) Hii ingekuwa kutoa manufaa na vitendo ya GI katika mipango ya lishe. "Tabla ya ""Values"" iliyoundwa na Foster-Powell na Miller" Uwezekano wa kubadilika kwa sukari ya sukari ni 85-111. Kwa mfano, glukozi ni moja ya wanga unaopimwa kwa usahihi zaidi. Takwimu katika meza za GI zimekusanywa kwa miaka mingi kutoka maabara mbalimbali duniani kote. Hii inamaanisha kwamba viwango vya GI vimetokana na bidhaa tofauti, yaani, bidhaa, asili, masomo tofauti na vipimo tofauti kama ilivyojadiliwa hapo awali. Kiwango cha Glycemic Index (GI) ni chini ya 55 au chini ya 55 na ya kati ya 56 hadi 69 na ya juu ya 70 au zaidi ya 70 na inaweza kuwa na athari mbaya kwa afya ya binadamu. Mfano wa hii inaonekana katika karoti ambayo kutokana na thamani yao ya juu ya GI watu huwa na kuepuka, wakati karanga salted ni kupatikana kuwa vyakula bora kulingana na GI. Kwa mfano, karoti ina kiwango cha GI cha 101, lakini ili kupata 50g ya wanga kutoka kwa karoti, unahitaji kula 575g, yaani, karoti 9 za ukubwa wa kawaida. Peanuts zina GI ya 21, na ili kupata wanga 50 kutoka kwa karanga unahitaji kula 500g. Kiasi hiki kinatoa 2925 kcal, ambayo 245g ni mafuta. Hiyo ni zaidi ya kiasi cha nishati ambacho watu wengi hutumia kila siku. "Jarvi et al. (1998): ""Kila kitu kinaweza kuwa na thamani ya afya, lakini sio tu kwa sababu ya thamani yake ya GI.""" Kwa hiyo, ni muhimu kuzingatia kwamba bidhaa za chakula zinapaswa kuwa na kiwango cha chini cha glycemic ya angalau 15 g kwa kila kipimo cha chakula, na kwa vyema zaidi ya 20 g kwa kila kipimo cha chakula, kama vile mkate, nafaka, pasta, mchele na viazi. (Arvidsson-Lenner et al., 2004) Kwa kuongezea, kulinganisha maadili ya GI kwa ujumla inapaswa kufanywa ndani ya vikundi vya chakula sawa. Hii inazuia kutoelewana kama vile orodha nyeusi ya karoti kwa mfano. Katika fasihi hii pia imeshughulikiwa kwa kutumia dhana ya mzigo wa glycemic (GL). Tunda linapokomaa, wanga hubadilishwa kuwa sukari. "Kila aina ya matunda yana GI ya juu kuliko sukari, kwa hivyo kadiri kukomaa kunapoendelea, GI hupungua. ""Je, hii inamaanisha kwamba tutawaambia watu kwamba wanaweza kula matunda katika hatua fulani za kukomaa na sio katika zingine?" 4.3.-Kubadilisha ukubwa wa chembe za chakula kunaweza kuathiri kiwango cha GI. Kiasi cha GI cha kipenyo cha 1 inch cha viazi kinaweza kuongezeka kwa 25% kwa kuchoma kipenyo hicho. Kutumia matofaa yote, mchuzi wa matofaa, na maji ya matofaa husababisha mabadiliko makubwa ya sukari na insulini. Kwa hiyo, je, tutawaambia watu kwamba wanaweza kula aina moja ya chakula lakini si nyingine? Aina ya chakula, njia ya kusindika au hata njia ya kutayarishwa inaweza kuwa na athari ya kiwango cha GI. Aina tofauti za vyakula zinaweza kuwa na GI tofauti. Mfano mzuri wa hii ni mchele, ambapo uwiano wa amylose na amylopectin katika nafaka huathiri GI. Ili kuelewa hili tunahitaji kuwa na ufahamu wa muundo wa amylose na amylopectin. Amylose ni molekuli linear na vitengo D-glucose kushikamana katika (1 < 4) njia. Amylopectin ina viungo vya (1-4) na (-1-6) (Annison na Topping, 1994) hivyo kuifanya kuwa muundo uliogawanyika. Amylopectin ni rahisi zaidi hydrolyzed katika matumbo kwa sababu ya hii na inachukua juu ya GI ya juu. "Amelsvoort na Weststrate, 1992: ""Tabula ya kimataifa iliyotengenezwa na Foster-Powell ilionyesha jinsi portions 50g za mchele tofauti zinaunda safu ya GI kutoka 68 hadi 103." Hii hufanya kuchagua aina gani ya mchele kula ngumu sana, kama amylose na amylopectin uwiano si alibainisha juu ya ufungaji. 4.4.2 Utaratibu wa chakula Chakula kilichotengenezwa ni cha kawaida sana katika lishe ya Magharibi. Hali za usindikaji wa kiwango kikubwa ni tofauti sana na mbinu za kawaida za nyumbani. Kusaga, kugeuza, kushinikiza, au hata kutafuna kabisa mbegu au chakula kingine chenye wanga kunaweza kuharibu chembechembe hizo. Jibu la glycemic linaweza kubadilishwa, ikitegemea jinsi wanga unavyotengenezwa. Katika utafiti uliofanywa na Brand na wenzake, iligunduliwa kwamba chakula kinapochanganywa zaidi, majibu ya glycemic ni ya juu zaidi. Kwa mfano, mchele uliopikwa kwa kawaida ulikuwa na kiwango cha glycemic cha karibu 50, ingawa wakati unashughulikiwa katika bidhaa ya mchele wa haraka, hupanda hadi 85, na zaidi hadi karibu 93 kwa mviringo wa mchele. Hii ni tofauti kubwa sana kwa bidhaa zote mbili zilizotengenezwa. Wakati wa kujaribu kuunda lishe karibu na bidhaa za chakula za chini za GI kwa kupoteza uzito, vyakula vilivyotengenezwa havitazalisha uteuzi mwingi, kwani bidhaa nyingi zitatokeza kiwango cha juu cha GI. Aina na kiwango cha kupikia kinachofanywa kinaweza kuathiri GI. Mzunguko wa joto na baridi inaweza kusababisha starch retrogradation. Kwa mfano, viazi visivyopikwa haviwezi kuharibiwa na maji, ingawa wakati vinapopikwa, chembe za starch hujifanya kuwa gelatin na hivyo zinaweza kumeng'enywa kwa urahisi. Wakati wa kuchemsha, gelatinization inageuka na karibu 12% ya starch ya viazi inakuwa sugu kwa hydrolysis na haiwezi kufyonzwa. Kiasi cha joto, maji na hata wakati wa kupika pia inaweza kuathiri GI sana. "Kama ilivyoelezwa hapo juu, ""macronutrients"" ni viungo vya chakula ambavyo vinaweza kuwa na kiasi cha juu cha madini ya wanga, ambayo ni pamoja na madini ya wanga, ambayo ni pamoja na madini ya wanga." Coulston et al. (1984) inaonyesha kwamba, kadiri kiasi cha wanga katika chakula fulani kilivyo kikubwa, ikilinganishwa na protini na mafuta, ndivyo kiwango cha GI kilivyo kikubwa; na chakula cha mchanganyiko cha wanga, protini na mafuta kitakuwa na majibu tofauti ya glukosi kulingana na kiasi cha kila virutubisho. 4.5.1 Mafuta na protini Mafuta na protini huonekana kuchelewesha kutolewa kwa tumbo, ambayo kwa upande huathiri uondoaji wa insulini. Athari zao juu ya GI si muhimu sana isipokuwa kiasi kikubwa. Kwa mfano, Wolever na Bolognese, ambao walipata athari ya kupunguza GI, waligundua uhusiano wa kinyume kati ya fiber na GI wakati wa kujumuisha aina mbalimbali za vyakula vyenye wanga. Kwa hiyo, inadhaniwa kwamba bidhaa za nafaka nzima zinaweza kuzalisha GI ya juu sawa na mkate mweupe. Pia imekuwa inajulikana kwa muda mrefu kwamba nyuzi ni uwezekano wa kuzalisha mbalimbali ya athari metabolic. Kwa mfano, kwa mfano, kwa kawaida, glycogen ya sukari (kwa mfano, mkate mweupe) ni ya chini kwa kiwango cha 65, na glucose ni karibu 97, fructose ni 23 na lactose ni 46. Fructose (Foster-Powell & Miller, 1995) ni bidhaa ya chakula ya kawaida ya kienyeji, ambayo inapatikana katika vyakula vya kawaida. Kwa mfano, GIG inaonyesha athari ya glucose ya damu, ambayo ni sababu ya sababu ya metabolism ya fructose, ambayo huathiri mwili kwa njia tofauti. (Elliott et al., 2002) Kutokana na hii, ulaji wa fructose unaonekana kupunguza satiety ambayo inaweza uwezekano wa kusababisha ongezeko la jumla ya ulaji wa chakula, kukuza uzito. (Bray et al., 2004) Wazo hili linadokeza sana kwamba kufuata vyakula vya chini ya GI vinaweza kuwa na athari mbaya. Asidi ya asidi ya asidi ya asidi ya asidi ya asidi ya asidi ya asidi ya asidi ya asidi ya asidi ya asidi ya asidi ya asidi ya asidi ya asidi ya asidi ya asidi ya asidi ya asidi ya asidi ya asidi ya asidi ya asidi ya asidi ya asidi ya asidi ya asidi ya asidi ya asidi ya asidi ya asidi ya asidi ya asidi ya asidi ya asidi ya asidi ya asidi ya asidi ya asidi ya asidi ya asidi ya asidi. Hii kwa kweli hupunguza IG ya vyakula, ikiongeza tatizo jingine wakati wa kupanga mlo. Je, ni lazima tuwajulishe watu kiasi cha siki wanachoweza kuweka kwenye chakula chao? Kama tunavyoona, kuna mambo kadhaa, kuanzia usindikaji hadi kupika, hata chakula, ambayo huathiri GI. Hii inaweza kuongoza watumiaji katika habari bandia juu ya thamani ya meza ya GI, hivyo kuathiri mipango ya lishe. Glycemic Load: Glycemic Load (GLI) ni kiwango cha juu cha kiwango cha kiwango cha kiwango cha kiwango cha kiwango cha kiwango cha kiwango cha kiwango cha kiwango cha kiwango cha kiwango cha kiwango cha kiwango cha kiwango cha kiwango cha kiwango cha kiwango cha kiwango cha kiwango cha kiwango cha kiwango cha kiwango cha kiwango cha kiwango cha kiwango cha kiwango cha kiwango cha kiwango cha kiwango cha kiwango cha kiwango cha kiwango cha kiwango cha kiwango cha kiwango cha kiwango cha kiwango cha kiwango cha kiwango. Hii ndiyo sababu dhana ya mzigo wa glycemic ilitengenezwa. Inazingatia uwiano wa wanga kwa kila sampuli ya chakula. Vyakula vinavyopatikana kwenye orodha ya glycemic index vinaweza kuonekana kuwa na thamani ya uso, kwa hivyo watu wengi huepuka kwa sababu hii. Kwa kweli, parsnips ni nyuzinyuzi zisizoweza kumeng'enywa, na unapaswa kula kidogo ili kusababisha ongezeko kubwa la sukari ya damu. Hii ni kwa sababu GI inashughulikia athari kwa kila gramu ya 10-50 ya wanga badala ya athari kwa gramu ya parsnip. "Kama ilivyoelezwa katika utafiti wa ""Glycemic Load"" (Salmeron et al., 1997), kiwango cha glycemic kinahitajika kwa ajili ya kulinganisha na kiwango cha glycemic ya chakula." GL inatoa uwezekano wa kulinganisha athari ya glycemic ya sehemu halisi ya vyakula tofauti, kulingana na kiasi cha wanga katika kipimo kimoja mara GI ya chakula. Spaghetti ina GI ya chini kuliko viazi vilivyokaangwa, lakini sehemu ya kawaida ya spaghetti ni kubwa kuliko sehemu ya kawaida ya viazi. (Arvidsson-Lenner et al., 2004) Kwa hivyo, GL inaweza au haiwezi kutofautiana kati ya vyanzo hivi viwili vya wanga, kulingana na maadili ya GI inayotumika na ukubwa wa sehemu. Kuchukua dhana ya GL katika mipango ya lishe itakuwa wazo la busara, ingawa bado inazalisha matatizo kuhusiana na mambo yaliyojadiliwa ambayo huathiri majibu ya glukosi ya chakula. Matumizi ya GL badala ya GI pia inaweza kusababisha kupungua kwa matumizi ya wanga, kwani itakuwa njia ya kupunguza GL ya jumla ya lishe. Kwa mfano, ikiwa chakula chenye GI ya juu na chakula chenye GI ya chini vina GL sawa, hazitakuwa na athari sawa ya kimetaboliki kwenye mwili. Kama ilivyojadiliwa hapo awali, majibu ya insulini yana uhusiano fulani na majibu ya glukosi. Kwa sababu ya kuongezeka kwa viwango vya insulini, chakula cha chini cha GI kinapendekezwa (Wylie-Rosenthal, 2004). Chakula cha chini cha GI pia huamini kupunguza njaa au kukuza ukarimu, na hivyo kupunguza ulaji wa nishati (Flint et al., 2004). Bado kuna mjadala ikiwa GI ni chombo muhimu katika kupoteza uzito. Utafiti wa utafiti wa uchunguzi uliofanywa na Ma et al. Katika utafiti huo, watu wazima 572 wenye afya nzuri walichunguzwa kwa miaka miwili. Chakula hicho kilikuwa na kiwango cha chini cha GI ambacho mara nyingi kilikuwa na vyakula vyenye nyuzinyuzi nyingi. Fiber inahusiana na kuongeza satiety kwa hiyo uhusiano kati ya vyakula vya chini ya GI na kuongezeka kwa satiety haikuweza kuamuliwa. Hii ni suala muhimu kwani inaaminika nguvu ya lishe ya chini ya GI ni kuongeza satiety na hatimaye kupunguza tabia za kula. 6.1 Chakula cha mchanganyiko Matumizi ya GI na matumizi yake kwa ajili ya chakula cha mchanganyiko ni debatable. Hata imegunduliwa kwamba GI huathiriwa wakati unaingizwa katika chakula na hata maji yanaonekana kuongeza GI. HOLLENBECK & COULSTON, 1991: Katika utafiti uliofanywa na Flint et al., 2004 lengo kuu lilikuwa kuchunguza umuhimu wa viwango vya meza ya GI kwa GI iliyopimwa katika chakula cha asubuhi. Utafiti huo ulionyesha kuwa GI ya chakula cha mchanganyiko kwa kutumia viwango vya meza haikutabiri GI iliyopimwa ya chakula, kwa hivyo wanga hauchezi jukumu muhimu zaidi kwa GI katika chakula cha mchanganyiko cha kiamsha kinywa. Uchunguzi huu unaonyesha ugumu wa kutumia viwango vya meza ya kimataifa kutabiri GI ya chakula maalum cha mchanganyiko katika maisha yetu ya kila siku. Hii ni muhimu kutambua wakati kujaribu kuendeleza mlo kulingana na thamani meza ya chakula chini ya GI kupoteza uzito. Kwa kweli, hii ni mada ya moto kwa ajili ya kupoteza uzito, kwa nadharia inaonyesha kwamba huongeza satiety na hivyo kupunguza njaa. Ingawa kutumia index ya glycemic na ujuzi mdogo wa mambo ambayo huathiri kiwango cha chakula, kuelewa mzigo wa glycemic na kuelewa uhusiano wa chakula cha wanga inaweza kuwa na majibu ya insulini haifanyi kuwa wazo rahisi kwa ajili ya kupanga chakula ili kupoteza uzito. Kama GI ilikuwa virutubisho badala ya kipimo cha athari kwa sukari ya damu, ingekuwa rahisi zaidi kuitumia. Hata hivyo, si virutubisho na haiwezi kupimwa kama hivyo. Inachukua juhudi nyingi kupima GI ya bidhaa moja ya chakula, achilia mbali chakula, na tunaweza kuona kwamba matokeo ni rahisi sana kuathiriwa. Umuhimu wa GI katika kudumisha uzito au kupoteza uzito lazima uchunguzwe zaidi. Ni muhimu kukumbuka kwamba kiwango cha glycemic ni kipimo cha kawaida cha chakula cha kawaida. Inatupelekea hatua moja karibu zaidi na jibu. Hata hivyo, mpaka tuweze kupata picha kamili juu ya athari za vyakula tofauti kwenye miili yetu, kufuata lishe ya chini ya GI ili kupoteza uzito haijulikani kwa usahihi. AMELSVOORT, J. V. na WESTSTRATE, J. (1992) Amylose-amylopectin uwiano katika mlo huathiri postprandial vigezo katika wajitoleaji wa kiume. American Journal of Clinical Nutrition, 55, 712-718 (Jarida la Marekani la Lishe ya Kliniki, 55, 712-718) Anison, G. & Topping, D. (1994) jukumu la lishe ya wanga sugu: muundo wa kemikali dhidi ya kazi ya kisaikolojia. Annual Review of Nutrition, 1429-320 (Utafiti wa Mwaka wa Chakula, 1429-320). ARVINSON-LENNER, R., ASP, N. G., AXEL-SEN, M., BRYNGELSSON, S., HAAPA, E. & JÄR-VI, A. Kiwango cha Glycemic Index (GDI) Uhusiano wa afya, mapendekezo ya lishe na uandishi wa chakula. Scandinavian Journal of Nutrition, 48 na 84-94. BJORK, I., LILJEBERG, H. & OSTMAN, E. (2000) Chakula cha chini cha glycaemic. British Journal of Nutrition, 83, s149-155 (Jarida la Uingereza la Lishe, 83, S149-155) BRAND-MILLER, J. C., HOLT, S. H., PAWLAK, D. B. & McMillan, J. Kiwango cha Glycemic na Uzito (2002) American Journal of Clinical Nutrition, toleo la 78, toleo la 281, toleo la 285. "Brad, J. C., Nicholson, P. L., Thorburn, A. W. & Trusswell, A. S. (1985) ""Utaratibu wa Chakula na Kiashiria cha Glycemic.""" "Jarida la ""The American Journal of Clinical Nutrition"" la mwaka wa 1992 na ""The American Journal of Clinical Nutrition"" la mwaka wa 1991 na ""The American Journal of Clinical Nutrition"" la mwaka wa 1991 na ""The American Journal of Clinical Nutrition"" ya mwaka wa 1991." BRAY, G. A., NIELSEN, S. J. POPKIN, B. M. 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