The glycemic index (GI) is an indicator used to classify carbohydrate-containing foods according to their ability to raise blood glucose levels after ingestion. Developed in the 1980s, this nutritional tool has become essential for understanding the impact of food on metabolic health, preventing blood glucose spikes, and formulating products tailored to specific needs (diabetes, weight management, functional nutrition). This article details the physiological mechanisms related to blood glucose, the factors influencing the GI, in vivo and in vitro , and the practical implications for manufacturers. Particular emphasis is placed on laboratory glycemic index measurement , including the various analytical approaches available—notably the Englyst test—and their strategic role in developing low-GI products that comply with regulatory requirements.
Table of Contents
What is the glycemic index?
Definition and origin
The glycemic index was introduced in 1981 by Professor David Jenkins of the University of Toronto. His aim was to provide a system for classifying carbohydrate-rich foods according to their ability to raise blood glucose levels after ingestion. The GI of a food corresponds to the area under the curve (AUC) of blood glucose over two hours after consuming a portion of the food containing 50 g of available carbohydrates, compared to the AUC obtained after ingesting 50 g of pure glucose (reference value = 100).
In practical terms, the glycemic index measures the postprandial glycemic response, that is, the rise in blood glucose levels within two hours of eating a food. The greater and more rapid this rise, the higher the food's GI.
Understanding blood glucose and its physiological role
Blood glucose refers to the concentration of glucose in the blood. In a healthy person, fasting blood glucose is between 0.70 and 1.10 g/L. After a meal containing carbohydrates, these are broken down during digestion into glucose, which is then absorbed by the intestine and enters the bloodstream. The rise in blood glucose triggers the pancreas to secrete insulin, a hormone responsible for regulating blood sugar levels by promoting its use or storage.
When blood sugar rises too quickly after a meal (glycemic spike), the body must produce a large amount of insulin to bring it down, which can eventually lead to metabolic disorders such as insulin resistance, type 2 diabetes or weight gain.
Method for calculating the glycemic index
The glycemic index is calculated experimentally. Volunteers consume a portion of a test food containing 50 g of available carbohydrates. Their blood glucose levels are measured at regular intervals over two hours. A curve representing blood glucose over time is then plotted. The area under this curve (AUC) is compared to that obtained with pure glucose, which is used as a reference.
The calculation formula is as follows:
GI = (AUC food tested / AUC glucose) × 100
For example, if the glycemic curve of a food covers an area representing 60% of that of glucose, its GI is 60. This measurement must be carried out under standardized conditions (prior fasting, controlled physiological conditions) to guarantee reliable and reproducible results.
There is a difference in reference points depending on the region:
- In Europe, glucose is used as the reference (GI = 100)
- In the United States, white bread is often the reference (GI = 100, glucose ≈ 143)
This difference requires adjustment if we want to compare the results from one table to another.
Factors influencing the glycemic index of foods
The glycemic index of a food is not a fixed value: it can vary considerably depending on several factors related to the intrinsic nature of the food, its preparation, and how it is consumed. Understanding this variability is essential for correctly interpreting glycemic index data and optimizing the formulation of low-glycemic impact products, both in the food and nutraceutical sectors.
The structure of carbohydrates
Not all carbohydrates have the same effect on blood sugar. Their chemical structure plays a central role:
- Simple carbohydrates (such as glucose, sucrose, or fructose) are rapidly digested and absorbed, generally resulting in a high GI, with exceptions such as fructose, which has a low GI but a high insulinemic index.
- Complex carbohydrates (such as starch) can have a low or high glycemic index (GI) depending on their composition. Starch is composed of two fractions:
- Amylose : linear chain, difficult to digest → lower GI
- Amylopectin : branched chain, rapidly hydrolyzed → higher GI
The ratio between amylose and amylopectin therefore directly influences the glycemic index of cereal products or starchy foods.
The cooking and processing method
Technological processes have a major effect on the glycemic index (GI) of foods:
- Cooking : the longer and at a high temperature a food is cooked, the more its starch gelatinizes, making it more digestible and increasing its glycemic index (GI). For example, pasta cooked al dente has a lower GI than overcooked pasta.
- Transformation : milling (white flour vs wholemeal), cooking-extrusion (breakfast cereals), or micronization modify the structure of carbohydrates and influence their absorption rate.
Manufacturers can therefore adjust their processes to limit the rise in GI, in particular by choosing gentle cooking conditions or by incorporating ingredients that slow down carbohydrate digestion.
The presence of fibers, lipids and proteins
The overall food matrix has a significant influence on the rate of digestion:
- Soluble fibers ( such as beta-glucans or pectin ) slow gastric emptying and limit enzymatic access to carbohydrates, thus reducing the GI.
- Fats slow down digestion by decreasing the rate of gastric emptying.
- Proteins can also modulate the glycemic response, by stimulating insulin secretion or by altering the overall digestion of the meal.
For example, a potato eaten alone will have a high GI, but if it is accompanied by olive oil and fiber-rich vegetables, the glycemic response will be moderate.
The level of maturity or processing of food
The ripeness of fruits and vegetables influences their simple sugar content:
- A green banana has a low GI (rich in resistant starch)
- A ripe banana has a higher GI (transformation of starch into simple sugars)
Similarly, fermented or sprouted foods may have a different GI than their raw form, due to internal enzymatic transformations.
The effect of a full meal (insulinemic index)
A food should not be studied in isolation: in reality, the glycemic response depends on the overall context of the meal . This is why we also talk about glycemic load (see part 3), and sometimes insulinemic index , which measures the total effect of a food on insulin secretion.
The same carbohydrates consumed in a meal rich in fiber, protein, or fat will result in a much lower glycemic response than if consumed alone.
Understanding these factors allows us not only to adapt our daily diet, but also to formulate industrial products with a moderate or low glycemic index (GI ) by adjusting the types of carbohydrates, processing methods, and the composition of the finished product. For professionals, these adjustments must be validated by rigorous analytical tests, particularly using in vitro GI prediction methods such as the Englyst test , which we will detail in the next section.
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Methods for measuring the glycemic index: in vivo and in vitro
The glycemic index (GI) can be determined in two main ways: either from clinical studies conducted in humans (in vivo), or through laboratory simulations of digestion (in vitro). Each of these methods has specific advantages, limitations, and contexts of use in the food industry, nutrition, and research.
In vivo measurement: the clinical reference method
Experimental principle
The reference method for establishing the glycemic index is based on tests performed on humans, according to a standardized protocol. It consists of:
- Have volunteers consume a test food containing exactly 50g of available carbohydrates.
- Measure their blood glucose at regular intervals (often every 15 to 30 minutes) during the two hours following ingestion.
- Compare the blood glucose curve obtained with that generated by the consumption of 50 g of pure glucose (reference GI = 100).
- Calculate the area under the curve (AUC) for both foods, and relate that of the tested food to that of glucose:
GI = (AUC food / AUC glucose) × 100
This method is scientifically recognized and remains the only validated way to obtain an “official” glycemic index.
Advantages and limitations
Benefits :
- Direct measurement of the actual glycemic response
- Allows for a precise clinical assessment of postprandial food behavior
Boundaries :
- High cost
- Time required (recruitment of volunteers, medical supervision)
- Significant inter-individual variability
- Unsuitable for testing a large number of formulations (R&D phase)
It is therefore mainly used to validate nutritional claims (such as "low glycemic index") within a regulatory framework, or to publish robust scientific data.
In vitro methods: prediction of the glycemic index in the laboratory
To overcome the limitations of clinical trials, several in vitro have been developed to estimate the glycemic behavior of foods based on digestion simulations . These tests are commonly used by manufacturers and analytical laboratories for preclinical screening .
Englyst method: simulated enzymatic digestion
The method developed by Englyst et al. (1992, 1996) is one of the most widely used. It is based on the analysis of the glucose level released during a simulated enzymatic digestion in the laboratory:
- The sample is subjected to digestion controlled by amylase and amyloglucosidase .
- Samples are taken at 20 minutes (G20) and 120 minutes (G120) to quantify the glucose released by spectrophotometry (GOPOD method).
- This data allows us to estimate the fractions of starch that are rapidly available , slowly available , and resistant , and to calculate an estimated GI .
This method is commonly used to test cereals, biscuits, breads, flours, or other starch-based products. However, it is not suitable for matrices low in starch or high in simple sugars.
INFOGEST models: triphasic digestion
Recent models like the COST INFOGEST 2019 incorporate a complete simulation of human digestion in three phases:
- Oral phase : salivary enzymes (amylase), chewing time
- Gastric phase : acidic pH, pepsin, simulated mixing
- Intestinal phase : pancreatic enzymes, bile, neutral pH
Laboratories like IGBalance use these models to predict the glycemic index in vitro from the glucose release profile during the entire simulated digestion.
The value of in vitro methods in formulation
These tests offer several advantages:
- Fast and reproducible : ideal for selecting low GI formulations in R&D
- Less expensive than an in vivo test
- Non-invasive
They are particularly useful for:
- Optimizing recipes during the development phase (bread formulas, energy bars, cereals, etc.)
- The selection of prototypes prior to clinical studies
- Comparative evaluation between different versions of a product
Main limitation : although effective in discriminating between products, the results cannot be used as a regulatory GI value without clinical validation.
Laboratory analysis services for glycemic index
Specialized laboratories offer analytical services based on these methods, including:
- The Englyst test (Glycemic Response)
- Complete simulated digestion according to INFOGEST , with rendering of glucose release curves, estimated GI, and summary of results
These services comply with the requirements of ISO 17025 standards and can be accompanied by additional analyses: moisture, total starch, dietary fiber, sugars, etc. They are particularly suited to the food, functional nutrition and nutraceutical industries.
Understanding the results of the glycemic index
Once the glycemic index (GI) of a food has been measured—whether by in vivo or in vitro methods—it is essential to fully understand its meaning, its nutritional interpretation, and its implications for health. This section aims to detail the classification of foods according to their GI, the factors that influence it, and the complementary concept of glycemic load.
Classification of glycemic indexes
The glycemic index (GI) allows us to classify foods into three categories according to their glycemic impact:
- Low GI (< 55) : slow digestion, moderate rise in blood sugar.
Examples: lentils, chickpeas, apples, plain yogurt, dark chocolate - Moderate GI (55 to 70) : intermediate elevation.
Examples: wholemeal bread, basmati rice, orange juice, ripe banana - High GI (> 70) : rapid digestion, marked blood sugar spike.
Examples: white bread, baked potatoes, corn flakes, watermelon
This classification is useful for guiding food choices towards products that are more conducive to metabolic health, particularly for people with diabetes or those trying to manage their weight. It is also invaluable for manufacturers wishing to formulate low-GI products that comply with modern nutritional guidelines.
Factors influencing the glycemic index of a food
It is important to note that the glycemic index (GI) of a food is not a fixed value. Several factors, often related to the processing method or the product's composition, can significantly alter its glycemic index.
Nature of carbohydrates
- Simple carbohydrates ( glucose, maltose) generally have a high GI.
- Complex carbohydrates ( starch) can have a variable glycemic index (GI) depending on their structure:
- Amylopectin is digested more quickly (high GI )
- Amylose , being more linear, slows down digestion (lower GI) .
Fiber, fat and protein content
- Dietary fiber : slows gastric emptying and carbohydrate digestion, lowering the glycemic index.
- Lipids and proteins : also slow gastric emptying, moderating the overall glycemic impact
Cooking method and processing
- Prolonged cooking or a softer texture increases the GI.
For example, "al dente" pasta has a lower GI than overcooked pasta. - Mashed potatoes have a higher GI than steamed chunky potatoes.
Temperature and cooling
- The formation of retrograded starch (particularly during the cooling of cooked starchy foods) lowers the glycemic index (GI).
For example, rice that is cooked and then cooled has a lower GI than freshly cooked hot rice.
Glycemic load: a complementary indicator to the GI
While the glycemic index measures the rate at which blood sugar rises, it doesn't take into account the actual amount of carbohydrates consumed in a serving. This is why the concept of glycemic load (GL) was developed.
Definition of glycemic load
Glycemic load takes into account both:
- The glycemic index of food
- The amount of carbohydrates present in a standard serving of this food
Formula:
CG = GI × (g of carbohydrates in a serving) / 100
Nutritional interpretation
- Low CG: < 10
- Moderate CG: between 11 and 19
- High CG: ≥ 20
A high GI food can therefore have a low glycemic load if it contains few carbohydrates in the portion consumed.
Example: Watermelon has a GI of 75, but a 100g serving contains few carbohydrates (approximately 7g). Its GL is therefore around 5, which is low.
This concept is particularly useful in the context of balanced diets or for diabetes management, as it provides a more complete view of the actual glycemic impact of meals.
Application in laboratory analysis
GI results (or estimated in vitro GI) are often provided by laboratories in the form of comprehensive reports , including:
- The protocol used (Englyst, INFOGEST, etc.)
- The glucose release curve
- The G20 / G120 values
- Calculation of estimated GI and glycemic load
- Recommendations on formulation optimization
This data can be used to:
- Validate a “low GI” claim (with clinical confirmation)
- Compare several prototypes of the same product
- Identify formulation levers to lower the GI (addition of fibers, starch reformulation, cooking adjustments, etc.)
Analytical services like those offered by YesWeLab thus make it possible to secure the development of nutritional products by integrating a rigorous scientific and regulatory approach.
Impact of the glycemic index on health
The glycemic index (GI) is not just a nutritional tool: it plays a crucial role in the prevention and management of many chronic diseases. This section details the main effects of a low-GI diet on metabolic, cardiovascular, and digestive health, as well as its usefulness in functional and preventative nutrition.
Blood sugar regulation and diabetes prevention
One of the main goals of the glycemic index is to help control postprandial blood glucose , that is, the rise in blood sugar levels after a meal. This is particularly relevant for people who:
- Diabetics (type 1 or type 2)
- In a pre-diabetic
- Exhibiting insulin resistance
Several clinical studies have demonstrated that a diet based on low-GI foods allows:
- Better blood sugar regulation
- A reduction in the level of glycated hemoglobin (HbA1c) , a marker of long-term glycemic control
- A decrease in blood sugar peaks, thus reducing insulin secretion
A meta-analysis published in BMJ in 2021 (Chiavaroli et al.) confirms that low GI or low glycemic load diets significantly improve glycemic parameters in diabetic patients, while reducing cardiovascular risks.
Weight management and obesity prevention
High glycemic index (GI) foods cause rapid spikes in blood sugar followed by sharp drops in blood sugar (reactive hypoglycemia), which can lead to:
- An early feeling of hunger
- An increase in appetite at the next meal
- Stimulation of lipogenesis (fat storage)
Conversely, a low glycemic index diet promotes:
- Longer-lasting satiety
- A reduction in snacking
- Better management of body weight
Nutritionists therefore frequently use the GI as a balancing lever in weight loss or weight stabilization diets .
Reduction of cardiovascular risks
Chronic elevation of postprandial blood glucose is associated with oxidative stress , systemic inflammation , and endothelial dysfunction , all factors involved in the development of cardiovascular diseases.
The effects of a low GI diet include:
- A decrease in blood triglycerides
- An improvement in the lipid profile (total cholesterol, HDL, LDL)
- A reduction in blood pressure
- An improvement in insulin sensitivity
Thus, adopting a low GI diet helps to limit atherosclerosis and prevent major cardiovascular events .
Glycemic index and digestive health
The composition of low-GI foods is often rich in soluble fiber , resistant starches, and complex polysaccharides. These components have beneficial effects on digestive health:
- Improvement of intestinal transit
- Stimulation of the gut microbiota (prebiotic effect)
- Reduction of intestinal inflammation
- Regulation of carbohydrate absorption
Low GI foods (legumes, vegetables, whole grains) are therefore recommended in the prevention of irritable bowel syndrome or metabolic disorders related to intestinal dysbiosis.
Applications in clinical and functional nutrition
The glycemic index is now a formulation criterion for health-oriented products. In the context of personalized nutrition , it is used to adapt carbohydrate intake to the specific needs of certain populations.
- Endurance athletes : maintaining energy without insulin spikes
- Pregnant women : prevention of gestational diabetes
- Obese or overweight patients : metabolic regulation
- Elderly people : maintaining metabolic autonomy
Nutraceutical and health industry companies are developing foods with a controlled GI to support metabolic functions, improve insulin response, or stabilize blood glucose.
Example: the development of low GI nutritional supplements for malnourished patients or those with type 2 diabetes.
In addition, some manufacturers emphasize the GI in their nutritional claims (e.g., “low glycemic index”), which often requires rigorous in vitro or in vivo analyses , such as those offered in the YesWeLab catalogue.
Industrial applications and analytical support by YesWeLab
Understanding the glycemic index (GI) is not limited to academic or nutritional interests. In a context where consumers demand healthier products, regulatory authorities are tightening requirements for health claims, and food innovations are proliferating, the GI is becoming a major strategic lever for the food industry . This section explores the practical applications of GI analysis in formulation, nutritional marketing, and regulatory compliance, with a focus on the services offered by YesWeLab.
Development of low glycemic index products
One of the main uses of glycemic index (GI) analysis is for the formulation of low glycemic impact products , intended for:
- Preventing blood sugar spikes in people with diabetes or pre-diabetes
- Reduce the overall glycemic load of the diet for better metabolic regulation
- Responding to market demand for “healthy” or “low GI” products
Manufacturers can thus test several versions of the same product (recipes, raw materials, cooking processes, grinding, fermentation, etc.) and select the one that generates the most moderate glycemic response In vitro methods are particularly useful in this context, as they allow for the rapid screening of several formulations before moving on to clinical validation.
Examples of applications:
- Cereal bars enriched with soluble fiber
- Biscuits or crackers made from legumes
- Slow-fermented wholemeal breads
- Beverages based on modified or resistant starch
Marketing value and nutritional claims
Having solid scientific data on the glycemic index also allows businesses to enhance the value of their products for consumers, through:
- Marketing claims include: “low glycemic index” , “blood sugar control” , etc.
- Nutritional and health claims, regulated by European legislation (EC No. 1924/2006)
However, for a claim relating to glycemic index (GI) to be admissible, it is imperative to provide robust scientific evidence , ideally from an in vivo In vitro results can serve as an exploratory basis , but are not sufficient on their own to validate a regulatory claim.
Regulatory compliance and nutritional safety
GI analysis is also relevant in the context of:
- From the development of dietary products or products intended for specific populations (diabetics, athletes, the elderly)
- Securing formulations in case of reformulation (sugar replacement, addition of fibers or polyols)
- From preparing registration dossiers for food supplements or functional foods
Some institutions or certification bodies now require an assessment of the glycemic response of products to validate their integration into a specific diet.
YesWeLab's analytical services: expertise, network and innovation
To support companies in analyzing the glycemic index and optimizing their products, YesWeLab offers comprehensive analytical support , thanks to its network of more than 200 partner laboratories accredited to ISO 17025 and COFRAC.
In vitro analyses and simulated digestion tests
- Implementation of standard or customized protocols (Englyst, Goni et al. method)
- Analysis of released glucose by spectrophotometry or HPLC
- Calculation of an estimated GI for each sample
- Delivery of complete deliverables: raw data, graphs, interpretive commentary
These services are particularly useful in the formulation or pre-selection phase , to guide R&D choices.
In vivo clinical studies
Thanks to its specialized partners, YesWeLab can conduct glycemic studies in humans , in compliance with official protocols (EFSA, FAO, ISO 26642), for:
- Obtaining an official IG (Geographic that can be used in a communication strategy or for filing a claim
- Documenting health records for innovative products
- Meeting the requirements of quality labels or regulatory authorities
To support manufacturers, formulators, and nutrition professionals in managing the glycemic index, YesWeLab offers a wide range of customized analytical services , performed in partnership with ISO 17025 accredited laboratories. From enzymatic digestion simulation (Englyst method) to the organization of in vivo , YesWeLab helps you precisely characterize the glycemic impact of your products, ensure the validity of your nutritional claims, and optimize your formulations. All analyses are accessible via a single digital platform, which centralizes your requests, tracks samples, and guarantees the traceability of results.
