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University of Illinois Extension

General Overview of Diabetes and Food

What is Diabetes?

Diabetes is a disease in which the glucose in the blood is higher than normal. High blood glucose is called hyperglycemia.

Glucose is a type of sugar that comes from foods containing carbohydrates and is found in everyone’s blood. Glucose is transported through the blood to all tissues and organs to be used for energy.

definition of diabetes

Blood glucose should not be too low (hypoglycemia) or too high (hyperglycemia). The body usually keeps blood glucose within a certain range. When blood glucose begins to rise above normal, it either enters cells to be used for energy, or it is stored. If it is stored for future use, it will be converted to glycogen or fat. Glycogen is a “quick fuel”that is found in muscle and the liver.

When blood glucose needs to enter a cell to provide it with energy, it often needs the help The body is normally able to control blood glucose levels using of a hormone called insulin. Insulin is released by the pancreas in response to increased levels of glucose in the blood. Insulin, blood glucose and the cell’s receptor all work together to move the glucose into the cell.

With diabetes, however, the body has trouble making or using insulin. For this reason, blood glucose levels rise and hyperglycemia occurs.

To imagine how glucose, insulin, and cell receptors work, think of your car. To park in your garage, you need a garage door and a garage door opener. Glucose is like your car, the cell receptor is like the garage door, and the insulin is like the opener.

If your body does not make enough insulin or if it does not work properly, glucose cannot get into your cells. Instead, glucose stays in your blood causing high blood glucose, or hyperglycemia. People with hyperglycemia have diabetes.

Carbohydrates, Proteins, and Fats all Contain Calories

To understand and manage diabetes well, you must know what happens to food when you eat. Food is made of

Carbohydrates, proteins, and fats all contain calories, and can all be used for energy. Carbohydrates are mostly in foods in the starchy foods groups, but also in vegetables, fruits, dairy foods, and sugars. The primary sources of protein are meats and dairy products. Fat can be found in dairy and meats. Fat can also be added to food, such as salad dressing or margarine. Fat can also be added when food is made, such as chips, cookies, or pizza.

Too many calories can cause weight gain. Weight gain usually also results in higher blood glucose levels because the body becomes less sensitive to insulin.

Vitamins, minerals, and water do not contain calories, cannot be used for energy, and do not affect blood glucose.


How does food turn into glucose?

When we eat, carbohydrates, proteins, and fats are digested and broken into smaller parts. Once broken down, these parts will affect blood glucose differently depending on how they are absorbed and how the body uses them.

Almost all the carbohydrate eaten will be converted into glucose in the body. The only carbohydrates not changed to glucose are those that cannot be digested, like fiber.

Protein and fat are not directly converted to glucose when digested. The effect on blood glucose is not as direct as eating carbohydrate. Eating too much protein and fat can lead to eating too many calories. Too many calories can make the cell insensitive to insulin. If the cell is insensitive to insulin, blood glucose can rise. So the amount of food that’s eaten can affect blood glucose – too much can lead to weight gain, insulin resistance, and higher blood glucose levels. Carbohydrates affect blood glucose, because carbohydrates are digested and broken into smaller parts that are primarily glucose units.

Is Glucose Bad for People with Diabetes?

No, glucose is not bad for people with diabetes. Everyone, including people with diabetes, needs glucose for energy. We need energy to play, exercise, and work, but we also need it for everyday body functions, like breathing, digesting, and making blood cells. Most of the glucose in our body comes from eating carbohydrates.

Everyone needs glucose for energy

People without diabetes are able to keep their blood glucose levels in a normal range regardless of the amount they eat. For people with diabetes, it is harder to keep blood glucose in a normal range. For this reason, people with diabetes need to balance the amount of food that they eat (especially food that contains carbohydrates) with their medication and activity level.

Why do Some People have High Blood Glucose Levels?

Glucose primarily comes from the food we eat. Mainly foods containing carbohydrates are broken down into glucose and used for energy. Once food is broken down into glucose, it enters the blood and is carried to all the cells of the body. However, in order for glucose to enter the cell, a special helper and cell receptor are needed. The helper that glucose needs to enter the cell is called insulin. Insulin is a hormone made by the pancreas. Cell receptors are like doorways into a cell. A cell can have many receptors.

How glucose and insulin normally work
How glucose and insulin normally work.

If your body does not make enough insulin or if the insulin or the cell receptors do not work the way they should, glucose cannot get into your cells. Instead, glucose stays in your blood causing hyperglycemia. A complete lack of insulin results in type 1 diabetes. Insulin or cell receptors that do not work properly result in type 2 diabetes.

Are there Different Types of Diabetes?

There are three main types of diabetes

Diabetes is not one single condition. Researchers are discovering many different reasons for diabetes to develop in one person rather than another. Some of these newer types of diabetes include maturity onset of the young diabetes, latent autoimmune diabetes, and chemically or surgically induced diabetes.

In all types of diabetes, blood glucose is higher than it should be. It is the reason that it is high that makes the types of diabetes different. Generally, however, there are three main types of diabetes:

Type 1 Diabetes

glucose can't get into the cell, because no insulin is produced by the body
Glucose can't get into the cell, because no insulin is produced by the body.

Type 1 diabetes can occur at any age, but is most often diagnosed early in life. Type 1 diabetes is called an autoimmune disease, because the immune system attacks the person’s own cells. In this type of diabetes, cells in the pancreas that produce insulin are the target of the body's immune system and are eventually destroyed. For this reason, people with type 1 diabetes produce no insulin so glucose cannot get into the cells.

type 1

Symptoms of type 1 diabetes include:

The symptoms of type 1 diabetes all relate to the high blood glucose levels. The glucose does not keep into the cell so the cell can’t do its work. This causes weight loss and tiredness. Because the glucose can’t get into the cell, the cell also signals that it needs glucose (food) and extreme hunger results. With the high blood glucose, there is an increased excretion of glucose into the urine. This also pulls more water with the glucose to keep the urine less concentrated. These two things cause increased thirst and increased urination.

Type 2 Diabetes

cell receptors are not working to let insulin-glucose enter the cell
Cell receptors are not working to let insulin-glucose enter the cell.

Type 2 diabetes is the most common form of diabetes. Ninety-five percent of the people who have diabetes have type 2. Although it was once thought that type 2 diabetes occurred only in adults, it is now known that people can develop type 2 diabetes at any age. With type 2 diabetes, the receptors on the cells become resistant to insulin and therefore cannot let glucose into the cell. Type 2 diabetes may also result if the body does not make enough insulin. Both problems with the cell receptor or with the amount of insulin produced, lead to high blood glucose levels. Being overweight and inactive increases the chance of developing type 2 diabetes.

Insulin resistance is a condition when normal insulin levels do not result in glucose entry into the cell. Higher than normal insulin levels in the blood occur in insulin resistance.

People who have insulin resistance are usually overweight or obese. They may have a normal blood glucose, be diagnosed as “pre-diabetes”, or have type 2 diabetes. People who have a normal blood glucose may have no symptoms of insulin resistance but usually develop pre-diabetes. Those with pre-diabetes usually develop type 2 diabetes. The exception to this progression occurs when overweight or obese people lose weight, eat a healthy diet, and exercise regularly.

Not everyone who is obese or overweight will develop insulin resistance, although a lot of people will. Genetics, diet, and activity levels all can play an important role in how well insulin and glucose interact.

type 2

Symptoms of type 2 diabetes include:

However, many people have no noticeable symptoms. This is because type 2 diabetes develops over a long time, usually several years. With these gradual changes in insulin resistance and glucose tolerance, a person may not notice symptoms as unusual, especially if they are older. For instance, blurry vision that could occur due to damage by high blood glucose to the eye could be mistaken for normal eye changes with aging. Another possible symptom of type 2 diabetes is slow wound healing. The high blood glucose prevents the normal healing process from occurring, and cuts or scrapes take a very long time to heal. Another possible symptom of type 2 diabetes in women is multiple urinary tract infections. The increased excretion of high levels of glucose also attract yeast, and can cause an infection.

Gestational Diabetes

Gestational diabetes is a form of diabetes that occurs during pregnancy. When a woman becomes pregnant there are many hormonal changes that take place. These changes, especially in the later stages of pregnancy, can affect the mother’s sensitivity to insulin. When the mother becomes resistant to insulin, her cells do not let glucose in and her blood glucose levels rise. When blood glucose levels rise above a certain level, gestational diabetes is diagnosed.

´╗┐pregnant woman with doctor

Doctors often check women’s blood glucose levels during their pregnancy because high blood glucose levels can cause complications during the pregnancy or after the baby is born. These complications include infants of high birth weight, increased risk of cesarean delivery, infant respiratory distress syndrome, infant hypoglycemia following delivery, and infant jaundice. The presence of fasting hyperglycemia greater than 105mg/dl may be associated with increased risk of fetal malformations and death. Although gestational diabetes usually goes away after the baby’s birth, women with this type of diabetes are at high risk for developing type 2 diabetes later in life.

How is Diabetes Diagnosed?

There are several types of tests that can be used to diagnose diabetes or pre-diabetes: a Fasting Plasma Glucose Test (FPG), an Oral Glucose Tolerance Test (OGTT), a random non-fasting plasma glucose test, and a hemoglobin A1c test. Any test should be repeated on at least two occasions. With two or more tests you can be sure the result is accurate.

a doctor is a person who can diagnose diabetes

According to the American Diabetes Association, a FPG test that results in a fasting blood glucose level between 100 and 125 mg/dl signals pre-diabetes (or 5.6 mmol/l and 6.9 mmol/l). A person with a fasting blood glucose level of 126 mg/dl or higher has diabetes (or 7.0 mmol/l).

In the OGTT, a person's blood glucose level is measured after a fast and two hours after drinking a glucose-rich beverage. If the two-hour blood glucose level is between 140 and 199 mg/dl (7.8 mmol/l and 11.1 mmol/l), the person tested has pre-diabetes. If the two-hour blood glucose level is 200 mg/dl or higher, the person tested has diabetes.

A random, non-fasting blood glucose of 200 mg/dL or higher may indicate diabetes (11.1 mmol/l). Symptoms of increased urination, increase thirst, and unexplained weight loss would support a diagonsis of diabetes. The random test is usually followed by either FPG or OGT for confirmation.

The hemoglobin A1c test measures the level of glucose in your blood for the past three months. Two hemglobin A1c values greater than 6.5% would diagnose diabetes. If one value is above 6.5% and one is below 6.5%, a FBG or OGT is usually ordered by the doctor. Having values between 5.7% and 6.4% is pre-diabetes.

What is Pre-diabetes?

Pre-diabetes occurs when blood glucose levels are higher than normal, but lower than levels used to diagnose diabetes. Other phrases sometimes used to describe pre-diabetes include “borderline diabetes” or “blood sugar a little high.” People with pre-diabetes are said to have impaired glucose tolerance and/or impaired fasting glucose levels. The American Diabetes Association defines impaired glucose tolerance and impaired fasting glucose as:

Impaired Glucose Tolerance

Impaired Glucose Tolerance is a 2-hour value of an oral glucose tolerance test that is greater than or equal to 140 mg/dl but less than 200 mg/dl.

Impaired Glucose Tolerance
Diagnostic categories of oral glucose tolerance tests.

Impaired Fasting Glucose

Impaired Fasting Glucose is a fasting blood glucose level of greater than or equal to 100mg/dl but less than 126 mg/dl.

Impaired Fasting Glucose
Diagnostic categories of impaired fasting blood glucose tests.

Pre-diabetes puts people at high risk for developing diabetes, but also gives them a head start on preventing this disease. People told that they have pre-diabetes can often bring their blood glucose levels back down to normal by balancing a healthy diet with physical activity and weight loss.

Can People with Diabetes Prevent the Complications of this Disease?

Diabetes is a serious disease that can affect the heart, circulation, eyes, feet, kidneys, nervous system, teeth, and gums. Diabetes affects so many organs and systems, because blood travels throughout the whole body. When blood glucose becomes too high, it can damage the blood vessels of the body and lead to cardiovascular disease (heart), retinopathy (eyes), amputations (legs and feet), kidney diseaseneuropathy (nervous system), and impotence (sexual function).

With the exception of the heart, high blood glucose damages these other organs because small blood vessels keep the organs working. The high blood glucose can damage these tiny blood vessels. When these are damaged, the oxygen, nutrients, and cell communication doesn’t work normally. This leads to retinopathy (eyes), amputations (legs and feet), kidney diseaseneuropathy (nervous system), and impotence (sexual function). The high blood glucose in the heart can increase fatty deposits and lead to cardiovascular disease.

risk of complications can be greatly reduced by keeping blood glucose levels within the target range

The risk of these complications can be greatly reduced by keeping blood glucose levels within the target range. For this reason, it is important to check blood glucose levels every day, and share these values with a health care provider.

Treatment Goals

There are certain goals set by the American Diabetes Association concerning the treatment of diabetes. They are:

  1. Maintain a near-normal level of blood glucose. This can only be achieved by balancing the amount of food eaten with the amount exercise performed, and the amount of insulin available and effective. The insulin can be either what the body makes (endogenous) or be insulin injections (exogenous). Oral glucose-lowering medications and physical activity can also help maintain normal glucose levels.
  2. Achieve and/or maintain optimal blood lipid levels.
  3. Achieve and/or maintain optimal weight.
  4. Prevent and/or treat complications of diabetes, such as retinopathy, kidney disease, neuropathy, and cardiovascular disease.
  5. Include healthy eating and maintain pleasure in eating.
  6. Be able to plan meals to fit your lifestyle.

Health care providers also recommend achieving normal blood pressure levels as a treatment goal.

goals concerning the treatment of diabetes

Meal Planning

The purpose of meal planning is to help you reach your personal blood glucose or weight goals. These goals should be discussed with your health care provider. How these goals are achieved will be different for everyone. Some may reach their goals by spacing their food intake and limiting portion sizes. Others benefit from a more specific meal plan. Serving sizes are always important when you plan your meals. Day-to-day variation in meals and snacks can lead to uneven glucose pattern.

Blood glucose levels are affected by the timing of meals and snacks
Blood glucose levels are affected by the timing of meals and snacks.

Four commonly used methods of meal planning include:

The Plate Method

The Plate Method: Breakfast The Plate Method: Lunch/Dinner

The plate method is one way that meals can be planned. For breakfast, starch should take up half of the plate, and meat or non-meat protein may take up 1/4 of the plate if desired. In the lunch and dinner plate method, vegetables should take up half of the plate, starch should take up 1/4 of the plate and meat or non-meat protein should take up another 1/4 of the plate. One serving of fruit and a cup of low-fat milk may accompany your meal. Although the plate method is relatively easy, portion sizes are still critical. The amount of food on your plate should vary according to the number of calories that you need each day. A recommended plate size is about 9 inches across (9 inch diameter). Try measuring your plates!

Starchy foods include: bread, rolls, rice, pasta, potatoes, yams, corn, lima beans, and cereals.

Vegetables include: lettuce, tomatoes, mushrooms, spinach, green beans, and broccoli.

Meat and non-meat protein foods include: chicken, beef, pork, fish, cheese, beans, tofu, and soy products that resemble meat or chicken.

Fruits include: oranges, applesauce, grapes, and peaches. More information on the plate method available at www.platemethod.com



MyPlate is a tool used to show the type and the amount of food that you need daily. Recently modified to take into consideration the new Dietary Guidelines for Americans, the new MyPlate has a plate divided into four sections and a glass for diary.

By visiting the website www.MyPlate.gov, you can enter your age, gender, and physical activity level and learn the amount of foods from each group that you should be eating each day. This website also offers tips about the types of foods within each group that are particularly important to eat. For example, MyPlate suggests that you:

Exchange Lists

Adapted from the American Dietetic Association www.eatright.org and the American Diabetes Association www.diabetes.org

The Diabetic Exchange List is a program that was developed by the American Dietetics Association and the American Diabetes Association. Exchange Lists are used to balance the amount of calories, carbohydrate, protein and fat eaten each day. The Exchange List book can be ordered from the American Diabetes Association website. To use the Exchange Lists, individuals must first talk with their doctor or dietitian about their dietary requirements and the number of calories that they need each day. Then the doctor or dietitian can explain how many servings from each group are needed to meet these daily requirements. Individuals can then use the Exchange Lists to determine what foods and in what amounts they need to eat each day.

There are six different Exchange List groups including the starch groups, the fruit group, the milk group, the non-starchy vegetable group, the meat and meat substitutes group, and the fat group. Each serving of food within an exchange group has about the same amount of carbohydrate, protein, fat, and calories as the other foods in that group. For this reason, foods within an exchange list group can be substituted for each other, but foods on one group list cannot be substituted for foods on another group list. For example, you may substitute eating a small apple for a small orange, because they are both one serving in the fruit group. However, you could not substitute eating a small apple for one slice of bread, because these foods are in different groups.

The amount and type of exchanges recommended each day are based on individual calorie needs, weight goals and the amount of physical activity performed daily

Exchange List Groups

The following are the six groups of the Diabetic Exchange Lists:

Starches ListStarches List (Includes breads, cereals, grains and starchy vegetables)
One exchange from this group has 15 grams of carbohydrates, 3 grams of protein, and 0-1g of fat for a total of 80 calories per serving.

Examples of one serving from this group include 1 slice of bread, 1/3 cup cooked rice, or 1/3 cup cooked pasta.

Fruit ListFruit List
One exchange from this group has 15 grams of carbohydrate for a total of 60 calories per serving. Foods in the fruit list do not contain any protein or fat.

Examples of one serving from this group include 1 small apple, 17 small grapes, or ½ cup of orange juice.

Non-starchy Vegetable List Non-starchy Vegetable List
One exchange from this group has 2 grams of carbohydrates, and 5 grams of protein for a total of 25 calories per serving. Non-starchy vegetables contain no fat.

Examples of one serving from this group include 1/2 cup cooked green beans, 1 cup raw lettuce, or 1/2 cup vegetable juice.

Milk List Milk List
Items on the milk list are divided into fat-free/low-fat milk, reduced-fat milk, and whole milk categories.

One fat-free/low-fat milk exchange has 12 grams of carbohydrates, 8 grams of protein, and 0-3g of fat for a total of 90 calories per serving. One reduced-fat milk exchange has 12 grams of carbohydrates, 8 grams of protein, and 5g of fat for a total of 120 calories per serving. One whole milk exchange has 12 grams of carbohydrates, 8 grams of protein, and 8g of fat for a total of 150 calories per serving.

Examples of one serving from the fat-free/low-fat milk exchange are 1 cup of non-fat skim or 1% milk, or 2/3 cup (or 6 ounces) of fat-free plain yogurt.

Meat and Meat Substitutes ListMeat and Meat Substitutes List
Meats are divided into very lean, lean, medium-fat, and high-fat lists based on the amount of fat they contain. High-fat exchanges should be eaten a maximum of three times a week.

One very lean meat exchange has 7 grams of protein, and 0-1 gram of fat for a total of 35 calories per serving. Examples of one very lean meat exchange are 1 ounce white meat chicken or turkey with no skin.

One lean meat exchange has 7 grams of protein, and 3 grams of fat for a total of 55 calories per serving. Examples of one lean meat exchange are 1 ounce lean beef or lean pork.

One medium-fat meat exchange has 7 grams of protein, and 5 grams of fat for a total of 75 calories per serving. Examples of one medium-fat meat exchange are 1 ounce dark meat chicken with skin, 1 egg, or 1 ounce of fried fish.

One high-fat meat exchange has 7 grams of protein, and 8 grams of fat for a total of 100 calories per serving. Examples of one high-fat meat exchange are 1ounce pork sausage, 1 ounce American cheese, or 1ounce of a hot dog.

Whereas one exchange from this list only refers to a 1 ounce portion of meat or meat substitute, a serving refers to 2 - 3 ounce portions of the foods in this list. A serving is often used in referring to the foods in this group because most people eat more than one ounce of meat or meat substitutes at a time.

Fat List Fat List
One exchange from this group has 5 grams of fat for a total of 45 calories per serving. Most items in the fat exchange list do not contain protein or carbohydrate.

Examples of one serving from this group include one teaspoon oil, one teaspoon butter, one teaspoon mayonnaise, or one tablespoon salad dressing.

Carbohydrate Counting

The Carbohydrate Counting method is similar to the Exchange List method in that they both use food groups. However, when you use Carbohydrate Counting, you keep track or "count" servings equal to 15 grams or 1 unit of carbohydrate The food groups that have carbohydrate and are counted are:

One serving from any of these three groups would count as one carbohydrate unit. For example if you ate two pieces of buttered toast and an 8 ounce glass of milk for breakfast, you would count that breakfast as having three carbohydrate units. Carbohydrate Counting differs from the Exchange List in that the amount of protein and fats in foods is not taken into consideration. So the butter on the toast consumed at breakfast would not be counted, because butter is in the fat group and does not contain carbohydrate.

Some examples of one carbohydrate unit would be:

If you are planning to use the Carbohydrate Counting method, you and your health care provider should decide how many servings of carbohydrate you should consume each day and at each meal for optimal health.

A basic carbohydrate counting book can be purchased on the American Dietetic Association's website or on the American Diabetes Association website.

Managing your Diabetes

How does someone with diabetes make sure they get the right amount of glucose, carbohydrate, or energy without their blood glucose getting too high? Remember that the food you eat is the energy that has to be balanced with exercise, which uses energy. The food that is best for someone who has diabetes isn’t magic or tasteless or unusual. It is regular food in the right amounts. Managing your diabetes will reduce your risk for complications of diabetes and help you feel better on a daily basis. The management of diabetes has three parts:

One way to see if you are managing your diabetes effectively is to monitor your blood glucose daily. Self-monitoring of blood glucose (SMBG) allows you to check your blood glucose level with a glucose meter and glucose testing strip and see if you are at, above, or below the normal blood glucose range. SMBG makes it easy for you to check your blood glucose wherever you are and whenever it is convenient for you. It is important to check your blood glucose level daily, but ask your doctor how many times a day you should check your blood glucose level for best monitoring.

One way to see if you are managing your diabetes effectively is to monitor your blood glucose daily

Another way to measure how effectively you are managing your diabetes is with the glycosylated hemoglobin or HbA1c test. Unlike SMBG, the HbA1c test is performed by your doctor or health care provider. This test gives you an approximate average of your blood glucose levels over the last 2-3 months. This average is given as a percentage. The American Association of Endocrinologists recommends that the goal for most people with diabetes should be a HbA1c result of less than 6.5 percent. The risk for diabetes complications increases when HbA1c results are consistently 6.5 percent or above.

For more information, visit:

Dietary Guidelines for Americans

Everyone has different needs, and should have individual treatment plans. The approach to a healthy diet for those who have diabetes is the same for everyone else. Following is a shortened version of the 2010 Dietary Guidelines for Americans developed by the Department of Health and Human Services (DHHS) and the United States Department of Agriculture (USDA). These three areas are the most important recommendations:

Dietary Guidelines for Americans

  1. Balancing Calories
    • Enjoy your food, but eat less.
    • Avoid oversized portions.
  2. Foods to Increase
    • Make half you plate fruits and vegetables.
    • Switch to fat-free or low-fat (1%) milk.
  3. Foods to Reduce
    • Compare sodium in foods like soup, bread, and frozen meals - and choose the foods with lower numbers.
    • Drink water instead of sugary drinks.

This site was last updated June, 2014.
This is a source of information only, and is not medical advice.