The Glycemic Index Diet: an overview

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What is the GI Diet?

The glycemic index (GI) diet is a dietary approach that involves choosing foods based on their impact on blood sugar levels. It involves choosing foods that have a low or moderate GI or glycemic load (GL), while avoiding foods that have a high GI or GL.

While the GI Diet does not place specific restrictions on fat and protein intake, it generally emphasizes the consumption of healthy fats, such as those found in nuts, seeds, avocados, and fatty fish, and lean protein sources, such as chicken, fish, beans, and legumes.

The GI Diet is considered a moderate diet, and involves consuming a moderate amount of carbohydrates (around 40-50% of total calories), a moderate amount of protein (around 20-30% of total calories), and a moderate amount of healthy fats (around 30-40% of total calories).

Some versions of the GI diet also emphasize consuming more foods that are high in fiber and protein, which can further slow down the absorption of carbohydrates and promote feelings of fullness.

What is Glycemic Index (GI)?

The glycemic index (GI) is a numerical value that represents how quickly and to what extent a food raises a person’s blood glucose level after it is consumed.

The GI measures the rate at which carbohydrates are digested and absorbed by the body and converted into glucose, which is then released into the bloodstream.

Foods with a high GI value cause a rapid increase in blood glucose levels, while foods with a low GI value cause a more gradual increase. The GI is based on a scale of 0 to 100, with pure glucose being the reference food with a GI value of 100.

Foods with a GI value of 70+ are considered high
Foods between 56 – 69 are moderate
Foods 55 or less are low

How is GI calculated?

To calculate the GI of a test food, a group of people are given a measured amount of the food containing a fixed amount of carbohydrates, usually 50 grams. The participants’ blood glucose levels are then monitored over the next two hours to measure the rate at which the food is digested and absorbed.

The area under the blood glucose response curve for the test food is then compared to the area under the curve for the reference food. This is done by calculating the incremental area under the curve (AUC) for the test food and dividing it by the AUC for the reference food. The resulting number is then multiplied by 100 to obtain the GI value for the test food.

The formula for calculating the glycemic index (GI) of a food is as follows:

GI = (AUC of test food / AUC of standard food) x 100

For example, if the AUC for a test food is 50 and the AUC for the reference food is 100, the GI value for the test food would be 50/100 x 100 = 50. This means that the test food raises blood glucose levels 50% as much as the reference food, which is white bread or pure glucose.

What is Glycemic Load (GL)?

Glycemic load (GL) is a measure of the amount of carbohydrate in a serving of food and how much it raises blood glucose levels. It takes into account both the glycemic index (GI) of the food and the amount of carbohydrate in a serving.

While GI only measures how quickly a food raises blood glucose levels, glycemic load also considers the amount of carbohydrates in a serving of that food. Foods with a high GI value but low carbohydrate content will have a low glycemic load, while foods with a low GI value but high carbohydrate content will have a high glycemic load.

How is GL calculated?

The formula for calculating glycemic load is:

Glycemic Load = (Glycemic Index x grams of carbohydrate per serving) ÷ 100

For example, watermelon has a high GI value of 72, but a low glycemic load because it contains very few carbohydrates per serving. A slice of watermelon weighing 120 grams contains about 6 grams of carbohydrates. So its glycemic load would be:

Glycemic Load = (72 x 6) ÷ 100 = 4.32

This means that a serving of watermelon has a low glycemic load, despite having a high GI value. In contrast, a serving of white rice has a high glycemic load because it has a high GI value and a high carbohydrate content.

GI vs GL

While glycemic index (GI) and glycemic load (GL) are related, they provide different information about how a particular food affects blood sugar levels. Therefore, it’s important to take into account both when making food choices.

The GI only takes into account how quickly a food raises blood sugar levels, while the GL also considers the amount of carbohydrates in a serving. This means that a food with a high GI value may have a low GL if it contains only a small amount of carbohydrates per serving.

By considering both GI and GL, people can make more informed food choices that can help maintain stable blood sugar levels. For example, a food with a low GI but high GL may not be the best choice for someone trying to manage their blood sugar levels because it contains a lot of carbohydrates. Similarly, a food with a high GI but low GL may be a better choice because it contains fewer carbohydrates.

It’s also worth noting that the GI and GL values of a particular food can vary depending on factors such as how the food is prepared, how much of it is eaten, and what other foods are consumed at the same time. Therefore, it’s important to use GI and GL values as a general guide when making food choices, rather than relying on them as absolute measures.

Health benefits

Generally speaking, choosing foods with a low GI and GL can help to maintain stable blood sugar levels and promote overall health and well-being, which can be beneficial for a variety of health conditions. Here are a few examples:

Diabetes: The GI diet can help slow the absorption of glucose into the bloodstream, preventing rapid spikes in blood sugar levels. This can help reduce the demand on the pancreas to release insulin, potentially helping to prevent insulin resistance and the development of type 2 diabetes.
Weight loss: The GI diet can promote feelings of fullness and satisfaction after meals, while still providing their bodies with the essential nutrients they need for optimal health. Additionally, the high fiber content of many low-GI foods can help improve digestion, promote feelings of fullness, and reduce the absorption of calories from other foods in the diet.
Cardiovascular disease: Consuming a diet that is high in high GI or GL foods can increase the risk of cardiovascular disease. This is because these foods can cause inflammation and oxidative stress, which can damage the lining of blood vessels and increase the risk of heart disease.
Polycystic ovary syndrome (PCOS): PCOS is a hormonal disorder that can cause menstrual irregularities, infertility, and weight gain. Consuming a diet that is high in low GI foods can help to regulate blood sugar levels and insulin production, which can improve symptoms of PCOS.
Cancer: Consuming a diet that is high in high GI or GL foods can increase the risk of certain types of cancer, including colorectal, endometrial, and breast cancer. This is because these foods can cause inflammation and oxidative stress, which can damage cells and increase the risk of cancer.
Neurodegenerative diseases: Consuming a diet that is high in high GI or GL foods can increase the risk of neurodegenerative diseases such as Alzheimer’s disease. This is because high blood sugar levels can cause inflammation and oxidative stress, which can damage brain cells and increase the risk of cognitive decline.
Acne: Consuming a diet that is high in high GI or GL foods can worsen acne symptoms. This is because high blood sugar levels can cause an increase in insulin production, which can increase sebum production and lead to clogged pores and acne.
Non-alcoholic fatty liver disease (NAFLD): Consuming a diet that is high in high GI or GL foods can contribute to the development of NAFLD, which can lead to liver damage and other health complications.
Asthma: Consuming a diet that is high in high GI or GL foods can increase the risk of asthma and exacerbate symptoms in people who already have the condition.
Irritable bowel syndrome (IBS): Consuming a diet that is high in low GI foods can help to alleviate symptoms of IBS, such as bloating and abdominal pain.
Osteoporosis: Consuming a diet that is high in high GI or GL foods can increase the risk of osteoporosis, as these foods can cause inflammation and reduce calcium absorption, which can weaken bones over time.
Chronic kidney disease (CKD): Consuming a diet that is high in high GI or GL foods can increase the risk of CKD and worsen symptoms in people who already have the condition, as high blood sugar levels can damage the kidneys over time

For diabetes

Diabetes is a chronic condition that affects the body’s ability to produce or use insulin effectively, resulting in high blood sugar levels. The consumption of foods with a high GI or GL can contribute to the development of diabetes by causing repeated spikes in blood sugar levels, which can lead to insulin resistance over time. Insulin resistance occurs when the body’s cells become less responsive to insulin, resulting in higher blood sugar levels.

Foods with a high GI or GL include processed carbohydrates such as white bread, white rice, and sugary drinks. These foods can cause a rapid increase in blood sugar levels, leading to a surge in insulin production. Over time, the repeated surges in insulin production can lead to insulin resistance and eventually diabetes.

Research has shown that consuming a diet that is high in low GI foods, such as fruits, vegetables, whole grains, and legumes, can reduce the risk of developing diabetes. These foods are digested more slowly and cause a slower and more gradual increase in blood sugar levels, which helps to keep insulin levels stable.

In conclusion, foods with a high glycemic index or load can contribute to the development of diabetes by causing repeated spikes in blood sugar levels and insulin production. A diet that is high in low GI foods can help to reduce the risk of developing diabetes and improve overall health.

For weight loss

Generally, the GI diet is best for weight maintenance, especially if you’ve already lost a large amount of weight. However, it can be helpful for weight loss for those starting out.

When we consume foods with a high GI or GL, our bodies experience a rapid spike in blood sugar levels, which can lead to an increase in insulin production. Insulin is a hormone that helps our bodies store energy as fat. So, consuming foods with a high GI or GL can lead to increased fat storage, which can contribute to weight gain and obesity.

Furthermore, foods with a high GI or GL can also increase our appetite, causing us to consume more calories than we need. This is because the rapid increase in blood sugar levels can lead to a subsequent drop in blood sugar levels, which can leave us feeling hungry and craving more food.

On the other hand, consuming a diet that is high in low GI foods can help with weight loss. This is because low GI foods are digested more slowly, causing a gradual increase in blood sugar levels and a more steady release of insulin. This can help to regulate our appetite and reduce cravings, leading to a decrease in calorie consumption and weight loss.

Low GI foods also provide more sustained energy, which can help us feel more satisfied and reduce the likelihood of overeating. In addition, many low GI foods are high in fiber, which can promote feelings of fullness and satiety, further aiding in weight loss.

In conclusion, foods with a high GI or GL can contribute to obesity by increasing fat storage and appetite, while consuming a diet that is high in low GI foods can aid in weight loss by regulating appetite, reducing cravings, and providing sustained energy.

GI and GL of foods

Keep in mind that GI or GL refers only to foods that contain digestible carbohydrate. For example, proteins and fats do not have glycemic indexes. Proteins and fats do not contain carbohydrates and therefore do not raise blood glucose levels significantly.

Dietary fiber is a type of carbohydrate that is not fully digested and absorbed in the small intestine, and therefore it does not have a GI or contribute to the GL of a food in the same way as other carbohydrates.

Here are some websites that are good resources for searching the glycemic index and/or glycemic loads of different foods:

Glycemic Index Foundation: This website provides a searchable database of over 2,500 foods and their glycemic index values. It also includes information on the glycemic load of different foods and tips for managing blood sugar levels.
University of Sydney: This website provides a searchable database of over 1,000 foods and their glycemic index values. It also includes information on the glycemic load of different foods and tips for using the glycemic index to manage blood sugar levels.
NutritionData: This website offers a searchable database of over 40,000 foods, including their glycemic index values and glycemic load. It also provides detailed nutritional information for each food, including calories, fat, protein, and fiber content.

High GI foods (avoid)

Here are some groups of foods that are typically higher in glycemic index (GI), and are typically avoided on the GI diet:

Refined carbohydrates: These include foods made from white flour and processed grains, such as white bread, bagels, crackers, and pasta. Their GI ranges from around 70 to 100.
Sugary foods and drinks: These include soda, candy, cookies, and other sweets. Their GI can range from around 65 to 100.
Potatoes: Both white and sweet potatoes have a high GI, ranging from around 60 to 90.
Tropical fruits: These include mangoes, pineapples, and papayas, which have a GI ranging from around 50 to 75.
Processed breakfast cereals: These include many popular breakfast cereals that are high in sugar, such as cornflakes, rice cereals, and instant oatmeal. Their GI can range from around 55 to 90.
Dried fruits: Dried fruits are often higher in sugar than their fresh counterparts, and can have a GI ranging from around 30 to 75, depending on the type of fruit and how it’s processed.

Low GI foods (allowed)

Here are some groups of foods that are typically lower in glycemic index (GI), and are typically allowed on the GI diet:

Non-starchy vegetables: These include leafy greens, broccoli, cauliflower, peppers, carrots, and others. They are generally low in carbs and have a GI ranging from around 0 to 30.
Whole grains: These include whole wheat, brown rice, quinoa, and others. They are less processed than refined grains and have a GI ranging from around 40 to 70.
Legumes: These include lentils, chickpeas, beans, and peas. They are high in fiber and protein and have a GI ranging from around 20 to 50.
Nuts and seeds: These include almonds, walnuts, chia seeds, flax seeds, and others. They are high in healthy fats, protein, and fiber and have a GI ranging from around 0 to 30.
Berries: These include strawberries, blueberries, raspberries, and others. They are low in carbs and sugar and have a GI ranging from around 20 to 40.
Dairy products: These include milk, yogurt, and cheese. They are high in protein and have a GI ranging from around 20 to 60.

How to lower GI or GL

Proteins and fats

The presence of proteins and fats can slow down the digestion and absorption of carbohydrates in a meal, which can result in a slower rise in blood glucose levels over time. This effect can lower the overall glycemic index and glycemic load of a meal.

For example, adding protein or fat to a high-GI food like white bread can slow down the digestion and absorption of the carbohydrates in the bread, resulting in a lower glycemic response overall.

Additionally, consuming protein or fat along with carbohydrates can help to increase satiety and delay hunger, which can lead to better blood sugar control and potentially lower overall food intake.

This is why including sources of protein and healthy fats, such as nuts, seeds, avocado, and lean meats, in meals and snacks can be beneficial for managing blood sugar levels and promoting overall health.

Fiber

Dietary fiber can help to lower the GI and GL of a food by slowing down the rate at which glucose is released into the bloodstream after a meal.

When we eat foods that are high in fiber, the fiber helps to slow down the rate at which glucose is absorbed from the small intestine into the bloodstream. This means that the rise in blood sugar levels is slower and more gradual, which can help to prevent spikes and crashes in energy levels and promote better blood sugar control.

Fiber also helps to promote feelings of fullness and satiety, which can help to prevent overeating and promote weight management. This is because fiber takes longer to digest than other nutrients and helps to keep us feeling full for longer periods of time.

Overall, including high-fiber foods in meals and snacks can help to lower the GI and GL of a meal, improve blood sugar control, and promote feelings of fullness and satiety.

Cooking and ripeness

The way food is cooked can have an impact on its glycemic index. Foods that are fried, for instance, tend to have a high fat content, which can slow down sugar absorption in the bloodstream and ultimately decrease the GI.

Meanwhile, roasting and baking can break down resistant starch, a type of starch that is commonly found in legumes, potatoes, and oats and resists digestion, leading to an increase in the GI.

However, boiling is thought to help retain more resistant starch, resulting in a lower GI than other cooking methods.

When cooking pasta or rice, the longer they are cooked, the more their starch content becomes digestible, leading to a higher GI. Therefore, it’s best to cook them until they are al dente, or firm when bitten into.

In addition to cooking methods, the degree of ripeness of fruits can also affect their GI, particularly with bananas. The amount of resistant starch in bananas decreases as they ripen, leading to a higher GI. For example, fully ripe bananas have a GI of 51, while under-ripe bananas have a GI of just 30.

Finally, highly processed foods tend to have higher GI and GL values than whole foods because processing can break down the food’s natural fiber and other nutrients. For example, white bread has a higher GI and GL than whole grain bread because it is made from refined flour.

Example 7 day diet plan

Here’s a sample 7-day meal plan that follows the principles of a low glycemic index (GI) diet:

Day 1:

Breakfast: Oatmeal with sliced banana, chopped nuts, and a drizzle of honey
Snack: Apple slices with almond butter
Lunch: Tuna salad with mixed greens, cucumber, and cherry tomatoes
Snack: Greek yogurt with blueberries and chia seeds
Dinner: Baked salmon with roasted Brussels sprouts and sweet potato

Day 2:

Breakfast: Scrambled eggs with spinach and whole grain toast
Snack: Carrot sticks with hummus
Lunch: Grilled chicken salad with mixed greens, avocado, and cherry tomatoes
Snack: Strawberries with cottage cheese
Dinner: Quinoa stuffed bell peppers with a side of green beans

Day 3:

Breakfast: Greek yogurt with sliced peaches and a sprinkle of cinnamon
Snack: Roasted chickpeas
Lunch: Lentil soup with whole grain crackers
Snack: Pear slices with cashew butter
Dinner: Grilled sirloin steak with roasted root vegetables

Day 4:

Breakfast: Whole grain waffles with fresh berries and a dollop of Greek yogurt
Snack: Hard boiled egg
Lunch: Chicken wrap with whole grain tortilla, lettuce, tomatoes, and avocado
Snack: Sugar snap peas with hummus
Dinner: Baked chicken thighs with roasted sweet potato and steamed broccoli

Day 5:

Breakfast: Smoothie made with Greek yogurt, frozen berries, spinach, and almond milk
Snack: Sliced bell pepper with hummus
Lunch: Lentil salad with mixed greens, cherry tomatoes, and feta cheese
Snack: Apple slices with peanut butter
Dinner: Grilled fish with mixed vegetables and quinoa

Day 6:

Breakfast: Egg and vegetable scramble with whole grain toast
Snack: Roasted pumpkin seeds
Lunch: Chickpea salad with mixed greens, cucumber, and cherry tomatoes
Snack: Banana with almond butter
Dinner: Grilled chicken with roasted asparagus and quinoa

Day 7:

Breakfast: Overnight oats with sliced strawberries and a drizzle of honey
Snack: Cottage cheese with blueberries
Lunch: Grilled vegetable and feta cheese wrap with whole grain tortilla
Snack: Celery sticks with hummus
Dinner: Beef and vegetable stir-fry with brown rice