Many observational studies have examined the association between GI and risk of chronic disease , relying on published GI values of individual foods and using the following formula to calculate meal or diet GI 9 :. Yet, the use of published GI values of individual foods to estimate the average GI value of a meal or diet may be inappropriate because factors such as food variety, ripeness, processing, and cooking are known to modify GI values.
In a study by Dodd et al. Besides the GI of individual foods, various food factors are known to influence the postprandial glucose and insulin responses to a carbohydrate-containing mixed diet. A recent cross-over , randomized trial in 14 subjects with type 2 diabetes mellitus examined the acute effects of four types of breakfasts with high- or low-GI and high- or low- fiber content on postprandial glucose concentrations.
Plasma glucose was found to be significantly higher following consumption of a high-GI and low-fiber breakfast than following a low-GI and high-fiber breakfast. However, there was no significant difference in postprandial glycemic responses between high-GI and low-GI breakfasts of similar fiber content In this study, meal GI values derived from published data failed to correctly predict postprandial glucose response, which appeared to be essentially influenced by the fiber content of meals.
Since the amounts and types of carbohydrate, fat, protein , and other dietary factors in a mixed meal modify the glycemic impact of carbohydrate GI values, the GI of a mixed meal calculated using the above-mentioned formula is unlikely to accurately predict the postprandial glucose response to this meal 3.
Using direct measures of meal GIs in future trials — rather than estimates derived from GI tables — would increase the accuracy and predictive value of the GI method 2 , 6. In addition, in a recent meta-analysis of 28 studies examining the effect of low- versus high-GI diets on serum lipids , Goff et al.
Therefore, a stricter use of GI cutoff values may also be warranted to provide more reliable information about carbohydrate-containing foods. The glycemic index GI compares the potential of foods containing the same amount of carbohydrate to raise blood glucose. However, the amount of carbohydrate contained in a food serving also affects blood glucose concentrations and insulin responses.
Yet, one serving of watermelon provides 11 g of available carbohydrate, while a medium doughnut provides 23 g of available carbohydrate. The concept of glycemic load GL was developed by scientists to simultaneously describe the quality GI and quantity of carbohydrate in a food serving, meal, or diet. The GL of a single food is calculated by multiplying the GI by the amount of carbohydrate in grams g provided by a food serving and then dividing the total by 4 :. Using the above-mentioned example, despite similar GIs, one serving of watermelon has a GL of 8, while a medium-sized doughnut has a GL of Dietary GL is the sum of the GLs for all foods consumed in the diet.
It should be noted that while healthy food choices generally include low-GI foods, this is not always the case. For example, intermediate-to-high-GI foods like parsnip, watermelon, banana, and pineapple, have low-to-intermediate GLs see Table 1. The consumption of high-GI and -GL diets for several years might result in higher postprandial blood glucose concentration and excessive insulin secretion.
A US ecologic study of national data from to found that the increased consumption of refined carbohydrates in the form of corn syrup, coupled with the declining intake of dietary fiber , has paralleled the increased prevalence of type 2 diabetes In addition, high-GI and -GL diets have been associated with an increased risk of type 2 diabetes in several large prospective cohort studies.
Moreover, obese participants who consumed foods with high-GI or -GL values had a risk of developing type 2 diabetes that was more than fold greater than lean subjects consuming low-GI or -GL diets However, a number of prospective cohort studies have reported a lack of association between GI or GL and type 2 diabetes The use of GI food classification tables based predominantly on Australian and American food products might be a source of GI value misassignment and partly explain null associations reported in many prospective studies of European and Asian cohorts.
Nevertheless, conclusions from several recent meta-analyses of prospective studies including the above-mentioned studies suggest that low-GI and -GL diets might have a modest but significant effect in the prevention of type 2 diabetes 18 , 25, A meta-analysis of 14 prospective cohort studies , participants; mean follow-up of Three independent meta-analyses of prospective studies also reported that higher GI or GL was associated with increased risk of CHD in women but not in men A similar finding was reported in a cohort of middle-aged Dutch women followed for nine years Overall, observational studies have found that higher glycemic load diets are associated with increased risk of cardiovascular disease, especially in women and in those with higher BMIs.
A meta-analysis of 27 randomized controlled trials published between and examining the effect of low-GI diets on serum lipid profile reported a significant reduction in total and LDL - cholesterol independent of weight loss Yet, further analysis suggested significant reductions in serum lipids only with the consumption of low-GI diets with high fiber content. In a three-month, randomized controlled study, an increase in the values of flow-mediated dilation FMD of the brachial artery, a surrogate marker of vascular health, was observed following the consumption of a low- versus high-GI hypocaloric diet in obese subjects A reduction in the expression of the gene coding for 3-hydroxymethylglutaryl HMG -CoA reductase, the rate-limiting enzyme in cholesterol synthesis , in blood cells further confirmed an effect for the low-GI diet on cholesterol homeostasis Evidence that high-GI or -GL diets are related to cancer is inconsistent.
A recent meta-analysis of 32 case-control studies and 20 prospective cohort studies found modest and nonsignificant increased risks of hormone -related cancers breast, prostate , ovarian, and endometrial cancers and digestive tract cancers esophageal , gastric , pancreas , and liver cancers with high versus low dietary GI and GL A significant positive association was found only between a high dietary GI and colorectal cancer Yet, earlier meta-analyses of prospective cohort studies failed to find a link between high-GI or -GL diets and colorectal cancer Another recent meta-analysis of prospective studies suggested a borderline increase in breast cancer risk with high dietary GI and GL.
Adjustment for confounding factors across studies found no modification of menopausal status or BMI on the association Further investigations are needed to verify whether GI and GL are associated with various cancers. Whether low-GI foods could improve overall blood glucose control in people with type 1 or type 2 diabetes mellitus has been investigated in a number of intervention studies.
A meta-analysis of 19 randomized controlled trials that included diabetic patients with type 1 diabetes and with type 2 diabetes found that consumption of low-GI foods improved short-term and long-term control of blood glucose concentrations, reflected by significant decreases in fructosamine and glycated hemoglobin HbA1c levels However, these results need to be cautiously interpreted because of significant heterogeneity among the included studies.
The American Diabetes Association has rated poorly the current evidence supporting the substitution of low-GL foods for high-GL foods to improve glycemic control in adults with type 1 or type 2 diabetes 51, A randomized controlled study in 92 pregnant women weeks diagnosed with gestational diabetes found no significant effects of a low-GI diet on maternal metabolic profile e.
The low-GI diet consumed during the pregnancy also failed to improve maternal glucose tolerance , insulin sensitivity , and other cardiovascular risk factors, or maternal and infant anthropometric data in a three-month postpartum follow-up study of 55 of the mother-infant pairs At present, there is no evidence that a low-GI diet provides benefits beyond those of a healthy, moderate-GI diet in women at high risk or affected by gestational diabetes.
Obesity is often associated with metabolic disorders, such as hyperglycemia , insulin resistance , dyslipidemia , and hypertension , which place individuals at increased risk for type 2 diabetes mellitus , cardiovascular disease , and early death 56, Lowering the GI of conventional energy-restricted, low-fat diets was proven to be more effective to reduce postpartum body weight and waist and hip circumferences and prevent type 2 diabetes mellitus in women with prior gestational diabetes mellitus Yet, the consumption of a low-GL diet increased HDL - cholesterol and decreased triglyceride concentrations significantly more than the low-fat diet, but LDL -cholesterol concentration was significantly more reduced with the low-fat than low-GI diet In other words, how quickly foods break down into sugar in your bloodstream.
A food with a high GI raises blood sugar more than a food with a medium to low GI. But the glycemic index does not take into account the amount of carbohydrate in a food.
So glycemic load is a better indicator of how a carbohydrate food will affect blood sugar. Here's a chart with carbohydrate foods' GL and GI. Q: If a food has a high glycemic index and a low glycemic load -- like graham crackers have a GI of 74 and a GL of 8. SW: Food ranked high on the GI may represent a huge portion of a food because GI is not based on standard serving sizes. Basically, if a food is ranked high on the glycemic index it has readily available carbohydrate for quick absorption.
However, the same food can have a low glycemic load because there may not actually be much total carbohydrate in a given serving of that food. A low GL is the better indicator that a food won't have much impact on blood glucose levels. The high GI is based on 5 cups of watermelon, not an actual serving size of 1 cup. The low GL means one serving of watermelon doesn't contain much carbohydrate, because it is actually mostly water.
The low GL indicates that a serving of watermelon won't have much impact on your blood sugar. Carrots are another example of a low GL food that many people think will raise their blood sugar a lot -- but it's not true.
That's because carrots have a high GI of However, what most people don't know, is that the GL for carrots is only 6. Keep in mind that a low GI doesn't mean a food is high in nutrients. You still need to choose healthy foods from all five food groups. A food's GI ranking only applies when a food is consumed on an empty stomach without any other type of food. As anyone who's ever eaten food knows, this isn't always how we eat. Pair a high GI food with a lean steak or a piece of salmon, a side of broccoli and a salad with vinaigrette, and the protein, fiber and fat all will serve to lower the glycemic index of the meal.
In addition, the glycemic index doesn't take into account how much we're actually consuming. Its role is to supplement blood glucose levels if they drop between meals especially overnight or during physical activity. The glycaemic index GI is a way of ranking carbohydrate-containing foods based on how slowly or quickly they are digested and increase blood glucose levels over a period of time — usually two hours.
The GI uses glucose or white bread as a reference food — it has a GI score of Carbohydrate-containing foods are then compared with this reference to assign their GI. This ensures all foods compared have the same amount of carbohydrate, gram for gram. Carbohydrates that break down quickly during digestion have a higher glycaemic index. These high GI carbohydrates, such as a baked potato, release their glucose into the blood quickly. Carbohydrates that break down slowly, such as oats, release glucose gradually into the bloodstream.
They have low glycaemic indexes. The blood glucose response is slower and flatter. Low GI foods prolong digestion due to their slow breakdown and may help with feeling full. These ranges, along with some example foods, include:. These are examples of nutrition content claims and general level health claims, allowed by Food Standards Australia New Zealand under Standard 1. The Low GI Symbol and claims about the relationship of a low GI product and its effect on health is only available to packaged food products that meet strict nutritional and testing criteria.
This labelling is not compulsory for food companies to follow, so not all products that are eligible will display the symbol or make a claim. This is often the case for smaller companies who may not have the money to go through the necessary processes to be given the label. The amount of the carbohydrate-containing food you eat affects your blood glucose levels.
For example, even though pasta has a low GI, a large serving can still cause the blood glucose levels to rise more rapidly than a smaller serving. This is what is called the glycaemic load GL.
GL is based on the idea that a high GI food consumed in small quantities would give the same effect on blood glucose levels as larger quantities of a low GI food. Using a pasta example:. Here is another example, where both foods contain the same amount of carbohydrate but their GIs are different:.
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