With the rise in obesity and other eating disorders and metabolic diseases such as diabetes, methods for measuring the nutritional content of food has become more popular, and necessary. We count calories and carbs in order to lose weight and manage our health. Food journals have become a recommended method for tracking these calories, carbs, and other nutritional properties. Keeping track of the foods we eat is a daunting task, but there are food indexes that can help provide us with a record of certain nutritional components in the food and drinks we consume.
Glycemic Index (GI)
One such food index is the glycemic index, which has become a commonly recommended resource for diabetics, but there is also the glycemic load and the insulin index. These concepts, or tools, are closely related, but share distinct differences that make each one an invaluable resource. Each one carries its own benefits and limitations, and none is superior to the other. They are best used together. The glycemic index, glycemic load, and insulin index are most often associated with diabetes, but they are helpful for anyone who wants to increase their awareness of the foods they are eating and how it affects the body. Using the indexes wisely can help us prevent insulin resistance and complications that result from sudden spikes (increases) in blood sugar levels (also known as blood glucose levels).
When we eat, the food (carbohydrates, fats and protein) is broken down into smaller components or particles. Carbohydrates are broken down into glucose, which is released into the bloodstream. In response to the elevated blood glucose levels, the beta cells in the pancreas secrete the hormone insulin. This insulin is needed in order to regulate the glucose and promote its absorption into cells. It also plays a role in the uptake of amino acids (the building blocks of protein).
Prolonged elevated blood sugar levels can cause damage to blood vessels and can lead to nerve damage, kidney problems, vision problems, amputations, and more; while increased insulin demand or secretion can lead to insulin resistance or hyperinsulinemia, a condition where excess or increased levels of insulin circulate in the blood, which can result in higher triglyceride levels, hypertension, and hardening of the arteries.
The glycemic index or glycaemic index (GI) measures the potential impact the carbohydrate content of a food will have on blood sugar levels compared to a reference or standard food, generally pure glucose or white bread. In other words, it measures how quickly the carbohydrates in a certain food are digested and raise blood sugar levels after eating. The foods are ranked on a scale from 0 to 100, with a GI value of 100 representing pure glucose. All other foods are compared to this standard. The GI value of a food is determined by testing healthy groups of people with measured portions of a particular food containing 50 grams of available carbohydrate (or 25 grams for foods that contain a lower amount of carbohydrates) as well as a control food that provides the same amount of carbohydrates, and then arriving at an average.
A GI value of 55 or less is classified as being low; a GI value between 56 and 69 is considered medium or moderate; and a value of 70 or more is classified as high. High GI foods are digested and absorbed the fastest and result in a quicker elevation of blood sugar levels. Blood sugar levels may peak in an hour or less after eating. These include foods such as carrots, boiled or baked sweet potatoes, boiled white potatoes, graham crackers, rice cakes, white rice, baked potatoes, white bread, and many refined breakfast cereals.
Medium or moderate GI foods take longer to be digested and raise blood sugar levels. Blood sugar levels may peak in over an hour after eating. These foods include pineapple, beets, whole wheat bread, pita bread, couscous, black grapes, raisins, black-eyed peas, white spaghetti, honey, and brown, wild, or basmati rice.
Low GI foods are digested and absorbed the slowest. Blood sugar levels may not peak for several hours after eating. These include most fruits such as apples, oranges, blueberries, raspberries, cherries, apricots, pears, plums, and peaches; most non starchy vegetables such as celery, lettuce, green beans, mushrooms, onions, cauliflower, cabbage, broccoli, bell peppers, snow peas, etc; and most nuts and seeds. The exact GI value of food can vary depending on the source of the table you are referring to.
There is no way of properly estimating the GI value of food, and many online resources may list different values. This is due to the many factors that can influence the GI value of a food, including the type of starch in the carbohydrate; the type of sugar; the presence of fats and fibre; the variety, ripeness, and origin of the food; the acidity of the food; the particle size (whether the food is processed); whether the food is cooked or raw; the time of day you eat (your metabolism and insulin resistance can change throughout the day); and the foods you consume with it.
Starchy foods were once thought to be “complex” carbohydrates that digest slowly, but that is not always the case. There are two types of starch in foods, amylose and amylopectin, and amylose is more slowly digested. Different types of sugar present in foods also digest at different rates. Glucose syrup is digested and absorbed the fastest, followed by sugar or sucrose, and then fructose.
The presence of fat and fibre also make a difference in how quickly the carbohydrates in the food are digested, since fat slows the rate of stomach emptying, thus decreasing the rate at which starch is digested, and viscous fibre (a type of soluble fibre) increases the viscosity (thickness) of the contents of the intestines, which slows down the interaction between digestive enzymes and starch, and, consequently, slows digestion. Similar to fat, acidity in food slows down stomach emptying and slows down the digestion of starch.
Smaller particles of food, like what you would find in highly processed finely milled flours, are easier for the digestive enzymes to penetrate, and are thus digested and absorbed faster. Ancient grains and coarsely ground flours have larger particles and take longer to break down. Most processed foods have higher GI values. The method of food preparation and cooking can also change the GI of a food since cooking can increase the swelling of starch molecules in food and make it easier to break down. Mixing foods can also change the GI value of the meal. Low GI foods, such as vegetables that are full of fibre, can slow the digestion of high GI foods that are being eaten at the same time, resulting in a medium GI meal.
The GI values of foods are also based on an average from tests on groups of people, and they do not guarantee that your body’s response to certain foods will match the group average.
Despite these variables, the glycemic index still provides a basic guideline for choosing foods that put less strain on the pancreas, and the body. High GI foods can cause blood sugar levels to spike, which in turn forces the body to release a lot of insulin quickly in order to bring the blood sugar levels back down. Blood sugar levels may fluctuate as the liver and pancreas try to maintain balance, or, in the case of diabetes, particularly type 1 where the body may not be able to produce any insulin, the blood sugar levels may remain high and cause damage. For someone without diabetes, the constant release of insulin may still eventually exhaust the pancreas, and lead to the underproduction of insulin or insulin resistance and the future development of type 2 diabetes. The glycemic index becomes a handy tool for knowing which foods can cause this spike and what foods to be cautious of consuming. It can also help a diabetic match insulin action with the rate of digestion of the food so that there is enough insulin to cover the carbohydrate value of the foods eaten.
Two major limitations of the glycemic index is that it doesn’t take into account the nutritional content of food (potato chips have a GI value of 54, which is considered low, but they contain little nutrients) and typical serving or portion sizes. For instance, the GI value of a food is based on 50 gram carbohydrate quantities, which, in the case of carrots, would equate to roughly 1 1/2 pounds worth. Most people could not eat that many carrots at one time, and that is where the glycemic load or glycaemic load (GL) comes into play.
Glycemic Load (GL)
The glycemic load is similar to the GI, except that it takes serving sizes into account. It is calculated by taking the particular food’s GI value, multiplying it by the number of grams of carbohydrates in the serving size, and then dividing it by 100.
GL = (GI x amount of carbohydrate) ÷ 100.
A GI value of 10 points or less is classified as low and tends to have little impact on blood sugar levels; between 11 to 19 points is considered to have a medium GL value, and tends to have moderate impact on blood sugar levels; and 20 points or higher is classified as a high GL value and has major impacts on blood sugar levels, tending to cause spikes.
While a food may have a high GI value because the carbohydrates are quickly digested and absorbed when eaten, it can have a low GL value since there may not be many total carbohydrates in a given serving. Watermelon and carrots have a high GI value because the carbohydrates are quickly absorbed and raise blood sugar levels, but they have a low GL value because the carbohydrate amount in a single serving is relatively small. Many medium to high GI vegetables have a low GL value, while many cereals and grains have a higher GL value.
This method for calculating the foods potential effect on blood sugar levels is considered to be a better indicator of how carbohydrates affect blood sugar levels. Some fruits and vegetables may possess a medium to high GI value and many people may restrict their consumption solely because of that, but the GL value helps give a better idea of how these foods truly affect blood sugar levels based on the amount eaten. However, while the GL value provides further guidance in choosing foods that put less strain on the body, it still shares similar limitations to the GI value in that it doesn’t take into consideration the nutritional content in food. Foods such as popcorn and whole wheat flour bread have a low GL value, but they are still not healthy choices.
Both GI and GL values are considered to be highly correlated to insulin release. Foods that are high in GI and GL tend to signal a large insulin response. However, this is not always the case. Certain foods, particularly high protein foods, can elicit an insulin response that is disproportionately higher than its glycemic response. In other words, they can cause a high surge in insulin release despite having little to no glycemic content. The insulin response is an equally important aspect of digestion, since prolonged high insulin concentrations have been linked with an increased risk of cancer, hypertension, and other health risks. Another resource that helps us identify the insulin response generated by different foods is the food insulin index (FII).
Insulin Index (II)
The insulin index measures the postprandial (after meal) insulin response to a portion of the test food in comparison to a reference food. It is still relatively new and research on it is limited. The food insulin demand (FID) was also created to combine a food’s insulin index value with the kJ (kilojoules) in the portion size. The insulin index is often considered less important than the GI and GL values, but it plays a vital role in preventing beta cell and pancreatic exhaustion and failure.
The insulin index allows testing of foods with little to no carbohydrate value, such as eggs, beef and fish. The insulin surge that comes in response to large protein meals is believed to result from the digestion of the amino acids. Leucine is a particular branch chain of amino acids that signals the secretion of a large amount of insulin. The insulin stimulates the uptake of amino acids from the blood into muscle cells, which then stimulate new muscle growth.
Protein foods also cause the body to secrete glucagon, a hormone that opposes some of the potentially harmful effects of insulin and stimulates the uptake of amino acids into the cells of the liver. The pancreas and liver are able to maintain balance of insulin release, but, over time, this long-term exposure to high insulin concentrations can be hard on the body. Drastic fluctuations in insulin levels can also provoke feelings of hunger, causing people to overeat. Some of these low glycemic foods that cause high insulin surges may need to be avoided by insulin resistant individuals, and even those without current health problems may want to be careful of how much they eat in order to prevent future complications or strain on the body.
Other foods that have high insulin index values include jelly beans, pancakes, honeydew melon, potatoes, most breakfast cereals, baked beans, and dairy products such as milk, cheese, and ice cream. Both the protein and lactose (a type of sugar) content in dairy products are responsible for its stimulation of large amounts of insulin.
Because of the role that elevated insulin levels play on insulin resistance and the development of diabetes, some people consider it a better tool than the GI and GL values for managing blood sugar levels. But, like the GI and GL values, the insulin index also has its limitations. It was created in 1997, and currently doesn’t have the same extensive body of research on it as the GI, and it also doesn’t take into consideration the nutritional value of food. Bacon, peanuts and peanut butter, and bologna are all low on the insulin index, but they contain high amounts of fat and little nutrition. Peanuts are also a common allergen and can contain a toxin known as aflatoxin.
Takeaway
Many believe that they can achieve a healthy diet simply by eating a low GI or low GL diet, and others believe that they can eat as much of a food as they want as long as it has a low GI or low GL value. This can lead to an unhealthy diet if people restrict themselves of healthy, but high GI/low GI fruits and vegetables, and instead choose low GI/GL foods that offer little nutritional value. The FII, GL, and GI cannot replace studying nutrition and the individual components of food. The nutritional content in food is the most important factor to keep in mind.
These food indexes can nevertheless provide useful guidelines when making food choices. For someone who has diabetes or is concerned about insulin resistance, they may find that choosing a low GI/low GL fruit such as blueberries may be a better choice than choosing a high GI/low GL fruit such as pineapple. They may also find it beneficial to avoid foods high in the in FII such as beef, eggs, or fish despite have little to no glycemic content.
Food indexes such as the GI, GL, and the FII are a controversial topic with many misconceptions. The information they provide can be overwhelming, and each have their limitations or flaws, but, when used as a basic guideline, they can help us make wiser choices. You can begin integrating the concepts and information they provide by eating more fruits and non-starchy vegetables; limiting starchy vegetables and grains such as potatoes and rice; choosing fresh fruits and vegetables over processed or juiced; limiting or eliminating processed or refined foods; limiting or eliminating animal protein foods including beef, pork, milk, cheese, eggs, and fish; reducing the amount of “bad” fats such as saturated fats and replacing them with “good” fats; and choosing foods high in fibre. Instead of debating over which tool is best, incorporating each of them into your meal planning can help you in making better choices that benefit your body and your health.