The glycemic (glycaemic) index (GI; ) is a number from 0 to 100 assigned to a food, with pure glucose arbitrarily given the value of 100, which represents the relative rise in the blood glucose level two hours after consuming that food. The GI of a specific food depends primarily on the type of

carbohydrate A carbohydrate () is a biomolecule composed of carbon (C), hydrogen (H), and oxygen (O) atoms. The typical hydrogen-to-oxygen atomic ratio is 2:1, analogous to that of water, and is represented by the empirical formula (where ''m'' and ''n'' ...

it contains, but is also affected by the amount of entrapment of the carbohydrate molecules within the food, the fat, protein content of the food, the moisture and fiber content, the amount of organic acids (or their salts) (e.g., citric or acetic acid), and the method of cooking. GI tables, which list many types of foods and their GIs, are available. A food is considered to have a ''low GI'' if it is 55 or less; ''high GI'' if 70 or more; and ''mid-range GI'' if 56 to 69. The term was introduced in 1981 by

David J. Jenkins David J. A. Jenkins (born 20 July 1942) is a British university professor in the department of Nutritional Sciences at the University of Toronto, Canada. He is an advocate and researcher of plant-based nutrition. It is useful for quantifying the relative rapidity with which the body breaks down carbohydrates. It takes into account only the available carbohydrate (total carbohydrate minus

fiber Fiber (spelled fibre in British English; from ) is a natural or artificial substance that is significantly longer than it is wide. Fibers are often used in the manufacture of other materials. The strongest engineering materials often inco ...

) in a food. Glycemic index does not predict an individual's glycemic response to a food, but can be used as a tool to assess the insulin response burden of a food, averaged across a studied population. Individual responses vary greatly. The glycemic index is usually applied in the context of the quantity of the food and the amount of carbohydrate in the food that is actually consumed. A related measure, the

glycemic load The glycemic load (GL) of food is a number that estimates how much the food will raise a person's blood glucose level after it is eaten. One unit of glycemic load approximates the effect of eating one gram of glucose. Glycemic load accounts for ho ...

(GL), factors this in by multiplying the glycemic index of the food in question by the carbohydrate content of the actual serving.

Measurement

The glycemic index of a food is defined as the incremental area under the two-hour blood glucose response curve ( AUC) following a 12-hour fast and ingestion of a food with a certain quantity of available carbohydrate (usually 50 g). The AUC of the test food is divided by the AUC of the standard (either glucose or white bread, giving two different definitions) and multiplied by 100. The average GI value is calculated from data collected in 10 human subjects. Both the standard and test food must contain an equal amount of available carbohydrate. The result gives a relative ranking for each tested food. Foods with carbohydrates that break down quickly during digestion and release glucose rapidly into the

bloodstream In vertebrates, the circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the body. It includes the cardiovascular system, or vascular system, that consists of the heart an ...

tend to have a high GI; foods with carbohydrates that break down more slowly, releasing glucose more gradually into the bloodstream, tend to have a low GI. A lower glycemic index suggests slower rates of digestion and absorption of the foods' carbohydrates and can also indicate greater extraction from the liver and periphery of the products of carbohydrate digestion. The current validated methods use glucose as the reference food, giving it a glycemic index value of 100 by definition. This has the advantages of being universal and producing maximum GI values of approximately 100. White bread can also be used as a reference food, giving a different set of GI values (if white bread = 100, then glucose ≈ 140). For people whose

staple Staple may refer to: *Staple food, a foodstuff that forms the basic constituent of a diet *Staple (fastener), a small formed metal fastener **Surgical staple Arts, entertainment, and media *Staple (band), a Christian post-hardcore band **Staple ( ...

carbohydrate source is white bread, this has the advantage of conveying directly whether replacement of the dietary staple with a different food would result in faster or slower blood glucose response. A disadvantage with using white bread as a reference food is that it is not a well-defined reference: there is no universal standard for the carbohydrate content of white bread.

Accuracy

Glycemic index charts often give only one value per food, but variations are possible due to: * Ripeness — riper fruits contain more sugars, increasing GI * Cooking methods — the more cooked, or overcooked, a food, the more its cellular structure is broken, with a tendency for it to digest quickly and raise blood glucose more * Processing — e.g., flour has a higher GI than the whole grain from which it is ground as grinding breaks the grain's protective layers and the length of storage. Potatoes are a notable example, ranging from moderate to very high GI even within the same variety. * Consumption order — changing the order that foods are eaten was demonstrated to affect blood glucose levels, where eating starches or sugars first resulted in faster increases than when eaten after the rest of the meal More importantly, the glycemic response is different from one person to another, and also in the same person from day to day, depending on blood glucose levels,

insulin resistance Insulin resistance (IR) is a pathological response in which cells in insulin-sensitive tissues in the body fail to respond normally to the hormone insulin or downregulate insulin receptors in response to hyperinsulinemia. Insulin is a horm ...

, and other factors. The glycemic index only indicates the impact on glucose level two hours after eating the food. People with diabetes have elevated levels for four hours or longer after eating certain foods.

Grouping

GI values can be interpreted intuitively as percentages on an absolute scale and are commonly interpreted as follows: A low-GI food will cause blood glucose levels to increase more slowly and steadily, which leads to lower postprandial (after meal) blood glucose readings. A high-GI food causes a more rapid rise in blood glucose level and is suitable for energy recovery after exercise or for a person experiencing

hypoglycemia Hypoglycemia (American English), also spelled hypoglycaemia or hypoglycæmia (British English), sometimes called low blood sugar, is a fall in blood sugar to levels below normal, typically below 70 mg/dL (3.9 mmol/L). Whipple's tria ...

. The glycemic effect of foods depends on various factors, such as the type of

starch Starch or amylum is a polymeric carbohydrate consisting of numerous glucose units joined by glycosidic bonds. This polysaccharide is produced by most green plants for energy storage. Worldwide, it is the most common carbohydrate in human diet ...

(

amylose Amylose is a polysaccharide made of α-D-glucose units, bonded to each other through α(1→4) glycosidic bonds. It is one of the two components of starch, making up approximately 20–25% of it. Because of its tightly packed Helix, helical struct ...

versus

amylopectin Amylopectin is a water-insoluble polysaccharide and highly branched polymer of α-glucose units found in plants. It is one of the two components of starch, the other being amylose. Plants store starch within specialized organelles called amyloplas ...

), physical entrapment of the starch molecules within the food, fat and protein content of the food and organic acids or their salts in the meal. The presence of fat or soluble dietary fiber can slow the gastric emptying rate, thus lowering the GI. In general, coarse, grainy breads with higher amounts of fiber have a lower GI value than white breads. Many modern diets rely on the glycemic index, including the

South Beach Diet The South Beach Diet is a popular fad diet developed by Arthur Agatston and promoted in his bestselling 2003 book.Sandra Bastin for University of Kentucky Extension Service. August 1998; revised March 2004University of Kentucky Extension Service: ...

, Transitions by Market America and NutriSystem Nourish Diet. However, others have pointed out that foods generally considered to be unhealthy can have a low glycemic index, for instance, chocolate cake (GI 38), ice cream (37), or pure fructose (19), whereas foods like potatoes and rice have GIs around 100 but are commonly eaten in some countries with low rates of diabetes.

Application

Weight control

Dietary replacement of saturated fats by carbohydrates with a low glycemic index may be beneficial for

weight control Obesity is a medical condition, considered by multiple organizations to be a disease, in which excess Adipose tissue, body fat has accumulated to such an extent that it can potentially have negative effects on health. People are classifi ...

, whereas substitution with refined, high glycemic index carbohydrates is not. However, a 2023

Cochrane review Cochrane is a British international charitable organisation formed to synthesize medical research findings to facilitate evidence-based choices about health interventions involving health professionals, patients and policy makers. It includes ...

did not find that adoption of low glycemic index (or load) diets by people who are overweight or obese leads to more weight loss (and better fat control) than use of diets involving higher glycemic index/load or other strategies. In clinical management of obesity, diets based on a low glycemic index/load appear to provide better glycemic and inflammatory control than ones based on a high glycemic index/load (and therefore could potentially be more effective in preventing obesity-related diseases). In overweight and obese children, adoption of low glycemic index/load diets may not lead to weight loss but might potentially provide other benefits.

Limitations

Compared to quantity of carbohydrate

Depending on quantities, the number of grams of carbohydrate in a food can have a bigger impact on blood sugar levels than the glycemic index does. Consuming less dietary energy, losing weight, and

carbohydrate counting Carbohydrate counting or "carb" counting is a meal planning tool used in diabetes management to help optimize blood sugar control. It can be used with or without the use of insulin therapy. Carbohydrate counting involves determining whether a food i ...

can be better for lowering the blood sugar level. Carbohydrates impact glucose levels most profoundly, and two foods with the same carbohydrate content are, in general, comparable in their effects on blood sugar. A food with a low glycemic index can have a high carbohydrate content or vice versa; this can be accounted for with the

(GL) where .

Compared to insulin index

While the glycemic index of foods is used as a guide to the rise in blood glucose that should follow meals containing those foods, actual increases in blood glucose show considerable variability from person to person, even after consumption of identical meals. This is in part because glycemic index does not take into account other factors besides glycemic response, such as

insulin response The insulin index of food represents how much it elevates the concentration of insulin in the blood during the two-hour period after the food is ingested. The index is similar to the glycemic index (GI) and glycemic load (GL), but rather than relyi ...

, which is measured by the

insulin index The insulin index of food represents how much it elevates the concentration of insulin in the blood during the two-hour period after the food is ingested. The index is similar to the glycemic index (GI) and glycemic load (GL), but rather than relyi ...

and can be more appropriate in representing the effects from some food contents other than carbohydrates. In particular, since it is based on the area under the curve of the glucose response over time from ingesting a subject food, the shape of the curve has no bearing on the corresponding GI value. The glucose response can rise to a high level and fall quickly, or rise less high but remain there for a longer time, and have the same area under the curve.

References

External links

* – Searchable database of over 2600 foods with their glycemic index and load values.
List of low GI foods

Glycemic Index and Glycemic Load calculator
Total values for any combinations of foods and any number of servings are computed according t

.
Diabetes UK: Glycaemic Index and Diabetes
{{Authority control Diabetes Endocrinology Nutritional physiology