Understanding Glycaemic Index: Meaning, impact, and functionality

Dr. Ajay KohliJun 14, 2024

1. The Glycaemic Index (GI) is a measure of how quickly your body reacts to different carbohydrates present in food. The GI of a food item is rated on a scale of zero to 100; it can come in handy to control blood sugar better. By keeping track of the level of carbohydrates you consume in your food every day with the help of Glycaemic Index, you can lose weight, reduce blood sugar and cholesterol levels, and thereby reduce the risks associated with cancer, heart disease, and other illnesses.

Contents

• What does GI rating mean?
• How is the Glycaemic Index used?
• Benefits of Low-glycaemic food
• Digestion And Absorption Of Carbohydrates
• Factors affecting the GI of food
• Low-GI foods influence High GI foods
• Glycaemic load (GL)
• Glycemic Index of foods
• Effects of cooking and ripening
• Rules of Low-Glycaemic eating
• Frequently Asked Questions (FAQs)
• References

What does GI rating mean?

Food items are classified as low, medium, and high glycaemic foods; these are measured on a scale of 0 to 100. The lower the GI of the food, the better, indicating that the food may affect your blood sugar levels less.

GI ratings

Low: 55 or less

Medium: 56 to 69

High: 70 or above

Food items with high GI contain higher amounts of refined carbs, and sugar, and are quickly digested, while low GI food items are high in protein, fat, or fibre. Some foods do not fall under the category of GI rating, these include meat, fish, poultry, nuts, seeds, herbs, spices, and oils. Other factors considered while calculating a food item's GI rating include the ripeness, cooking method, type of sugar contained, and amount of processing.

How is the Glycaemic Index used?

Keeping a check on the GI ratings on the food items or product labels that you purchase can help you opt for healthier options. Comparing these values can be a helpful guide in making food choices. Always go for low GI food.

For example, when you get a sweet craving, it is better to go for a cupcake made of whole-wheat flour (GI: 45) than for a cupcake made of white wheat flour (GI: 77).

High GI foods: Food items that increase blood sugar

These include the following.

• Sugar and sugary foods

• Sugary soft drinks

• White bread

• Potatoes

• White rice

Low and medium GI foods: Food items that cause gradual increase of blood sugar levels

These include the following.

• Fruits (apples, bananas, oranges, lemons, berries, limes, grapefruit)

• Vegetables (broccoli, cauliflower, carrots, spinach, tomatoes)

• Pulses (lentils, chickpeas, peas, beans)

• Whole Grain foods, such as porridge oats

Benefits of Low-glycaemic food

Food items with carbohydrates that have a low GI value (55 or less) are more slowly digested, absorbed, and metabolised. As a result, the person's blood glucose levels rise at a slower and lower rate. 

Studies have shown that consuming low-glycaemic food provides multiple health benefits, and when combined with other nutritional guidelines such as including high-fibre foods, having low sugar intake, and low sodium intake, can improve an individual’s health to the maximum and prevent numerous diseases from occurring. 

Here are some of the benefits of low-glycaemic food items. 

Weight loss: Recent studies have shown that people who follow a low-GI diet may lose weight faster than those who do not. 

Better blood sugar and insulin control: Consuming foods with high GI will raise blood sugar levels faster and require more insulin to process. Low-GI diet may reduce blood sugar levels and help manage blood sugar levels better in people with type 2 diabetes. 

Reduced cholesterol levels: A low-GI diet may help lower total and LDL (bad) cholesterol levels, both of which are risk factors for heart disease.

Increased energy: Low-Glycaemic Index foods can boost your energy and keep you alert and focused throughout the day. It is a fact that we digest low-GI food items more slowly, this maintains a constant energy for body functions. Whereas high GI foods are digested and absorbed into the body at a faster rate, i.e., energy supply to the body is instant but not long-lasting. 

Improved mood: Some food items can improve your mood while some can bring you down. Mood is determined by serotonin levels, i.e., high serotonin levels boost one’s mood, while low serotonin levels have the opposite effect on the health and overall performance. 

Serotonin is linked to our foods (carbohydrates). Replacing high glycaemic foods (for example: sugary foods) with low-glycaemic foods (for example: nuts) aids in slow and sustained release of insulin, which will keep your blood sugar levels stable. This is followed by a gradual release of serotonin, allowing you to maintain a consistent mood throughout the day.

Digestion And Absorption Of Carbohydrates

The digestive system is crucial in breaking down carbohydrates from food and beverages into simple sugars, predominantly glucose. This process occurs through enzymatic action, where complex carbohydrates are broken down into their constituent monosaccharides, such as glucose, fructose, and galactose.

Once in the bloodstream, glucose is transported to various cells throughout the body to serve as a primary source of energy. The pancreas, an organ located behind the stomach, plays a pivotal role in regulating blood glucose levels. It secretes insulin in response to elevated blood glucose concentrations. Insulin acts as a key that unlocks cells, allowing glucose to enter and be utilised for energy production.

Glucose serves as the main fuel for vital organs and systems, including the brain, muscles, and nervous system. Without a steady supply of glucose, these organs would be unable to function optimally. Upon entering a cell, glucose undergoes cellular respiration, a process that involves the breakdown of glucose molecules in the presence of oxygen to generate adenosine triphosphate (ATP), the primary energy currency of the cell.

Excess glucose that is not immediately required for energy production is converted into glycogen for storage. The liver and muscle tissue serve as major reservoirs for glycogen storage. Glycogen acts as a readily available source of glucose that can be mobilised to maintain blood glucose levels during periods of fasting or increased energy demand, such as between meals or during physical activity.

The digestive system's breakdown of carbohydrates into glucose, insulin secretion by the pancreas, and glycogen storage by the liver and muscles ensure a constant and regulated supply of energy to support the body's metabolic needs.

Factors affecting the GI of food

Size, texture, and ripeness of food items affect GI; for example, ripe bananas have a higher GI than unripe ones. Fat, protein, fructose, and lactose lower GI. Acidic foods, like vinegar or lemon juice, slow digestion and lower GI. Phytates in whole grains delay absorption, reducing GI. 

Cooking and processing also impact GI; finely processed foods have a higher GI, while cooked foods cooled before consumption, like potato salad, have a lower GI than when hot. Understanding these factors helps manage blood sugar levels and choose foods with desirable glycemic responses.

Low-GI foods influence High GI foods

Combining low-GI and high-GI foods in a meal can moderate the overall glycemic impact. This blending effect is significant since meals typically consist of various foods. For instance, pairing high-GI cornflakes with low-GI milk mitigates the blood glucose spike caused by cornflakes alone. By balancing the GI of a meal, one can better manage blood sugar levels and promote sustained energy release. Understanding how different foods interact in meals empowers individuals to make informed dietary choices to support overall health and well-being.

Glycaemic load (GL)

The glycemic load (GL) concept goes beyond the glycemic index (GI) by considering both the type and quantity of carbohydrates in a portion. GL recognises that even foods with low GI can affect blood sugar levels if eaten in large amounts, while high GI foods may have a lesser impact when consumed in smaller portions. GL is calculated using the glycemic load formula. It is obtained by multiplying a food's GI by its carbohydrate content and dividing by 100.

For example, a standard serving of white wheat pasta has a GL of 19g, but reducing the portion size by half decreases the GL to 9.5g. Comparing foods with similar carbohydrate content, a small baked potato (GL = 12g) has a higher glycemic load than an apple (GL = 6g) due to its different GIs. Despite having the same amount of carbohydrates, the potato's higher GI causes a quicker rise in blood glucose levels compared to the apple. Understanding GL helps in managing blood sugar responses and creating well-balanced meals for overall health.

Glycemic Index of foods

Knowing the glycemic index (GI) of foods you frequently consume is beneficial when adhering to a low-glycemic diet. Key fruits like apples (36), strawberries (41), and oranges (43) offer lower GI options, while bananas (51) and mangoes (51) rank slightly higher. Among vegetables, boiled carrots (39) and plantains (66) represent contrasting choices. Grains vary widely, with barley (28) and quinoa (53) on the lower end and, white rice (73) and whole wheat bread (74) higher up. Legumes such as soybeans (16) and kidney beans (24) provide excellent options. Dairy selections like skim milk (37) and soymilk (34) offer lower GI alternatives compared to rice milk (86). Understanding these values helps in creating a balanced diet to manage blood sugar levels effectively.

Effects of cooking and ripening

Foods that are fried and high in fat can reduce the GI by slowing down sugar absorption. Roasting and baking can increase the GI by breaking down resistant starch, while boiling can lower it by retaining more resistant starch. Additionally, the ripeness of fruits, such as bananas, can affect their GI, with fully ripened bananas having a GI of 51, while under-ripe ones score just 30 due to their decreased resistant starch content. Understanding these factors can assist in effectively managing blood sugar levels.

Rules of Low-Glycaemic eating

Discussed below are some rules or tips that can help you follow a low-glycaemic diet.

It is advised to include the following in your diet:

• Non-starchy vegetables such as beans.

• Fruits such as apples, peaches, pears, and berries. 

• Tropical fruits with a lower Glycaemic Index like bananas, mangoes, and papaya instead of regular desserts.

• Consume grain in the least-processed state possible, such as whole-kernel bread, brown rice, whole barley, millet, and wheat berries. This can also include traditionally processed grains, for example the stone-ground bread, steel-cut oats and natural granola or muesli breakfast cereals. 

• Opt for healthy protein such as beans, fish, or skinless chicken at most meals.

• Choose foods with healthy fats, such as olive oil, avocados, nuts such as almonds, walnuts, and pecans. These need to be consumed in moderate amounts.

Limit the following in your diet:

• Saturated fats from dairy and other animal products

• White potatoes

• Refined-grain products, such as white breads and white pasta

• Fruit juice to not more than half glass/cup a day, better to consume whole fruit 

• Eliminate sugar-sweetened drinks

• Eliminate trans fats from diet, which are in fast food and many packaged foods

• Eat three meals a day with occasional snacking. Do not skip your breakfast.

Frequently Asked Questions (FAQs)

Here’s a list of common questions and answers about the Glycaemic Index.

Does cooking affect the Glycaemic Index of food?

Yes, certain foods and how they are cooked can affect the Glycaemic Index. Fat and fibre content tend to lower the Glycaemic Index (GI) of a food item. As a rule, the more cooked or processed a food, the higher the GI. 

Factors that affect the GI of a food item include the following.

• Ripeness and storage time: The riper a fruit or vegetable is, the higher the GI.

• Processing: Juice is higher in GI than whole fruit; mashed potato is higher in GI than whole baked potato; stone-ground whole-wheat bread is lower in GI than whole wheat bread.

• Cooking method: When compared to other cooking methods, boiling is thought to help retain more of the resistant starch and result in a lower GI. The longer you cook foods like pasta or rice, the more digestible the starch content becomes, and thus the higher GI value.

• Variety: Short-grain white rice has a higher GI than brown rice but converted long-grain white rice has a lower GI than brown rice.

Are Glycaemic Index and Glycaemic Load the same?

The Glycaemic Index (GI) ranks food items from 0 to 100 according to how quickly they are digested and enter your bloodstream. The higher the ranking of the food, the faster it raises your blood glucose levels. The Glycaemic Load (GL), on the other hand, considers the amount of carbohydrates (grams) in a single serving. For this reason, taking both GI and GL into consideration when selecting foods can help support an individual to maintain healthy blood sugar levels.

Is a low carbohydrate diet the same as a low-GI diet?

Low carbohydrates and low GI are not the same. Lower GI foods are not only good for glycaemic control, but its long term health benefits include reduced risk of chronic diseases. However, low carbohydrate diets have little to offer in that area, they may increase the risk of chronic diseases. 

Low-GI diets are more about the quality of the carbohydrate rather than the quantity. It is essential to check food labels, as they include both ‘lower carbohydrate’ and ‘lower GI’ for consumer information.

Should I avoid all high GI foods?

No. Some high GI foods, like most potatoes, brown rice, and watermelons are still nutritious. Consume them in moderation. High GI food items are also beneficial during prolonged physical activity or in the treatment of hypoglycaemia in diabetics. If you only eat food items with a low GI, your diet may be unbalanced. 

What are the limitations of using the Glycaemic Index?

One limitation of GI values is that they do not reflect the amount of food you are likely to consume. Watermelon, for example, has a GI value of 80, putting it in the category of foods to avoid. However, a typical serving of watermelon contains very few digestible carbohydrates.

References

• https://medlineplus.gov/ency/patientinstructions/000941.htm 

• https://www.health.harvard.edu/healthbeat/8-principles-of-low-glycemic-eating 

Disclaimer: The content on this page is generic and shared only for informational and explanatory purposes. Please consult a doctor before making any health-related decisions.

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