No area in nutrition is more controversial for a person with diabetes than carbohydrates. For years, the American Diabetes Association (ADA) told people with diabetes that they should eat 55 to 60 percent of their calories as carbohydrate. Other experts said that amount was too much or too little. The ADA has now modified its recommendation so that it says in the Clinical Practice Recommendations for 2012, "The recommended daily allowance for carbohydrate is 130 grams per day and is based on providing adequate glucose as the required fuel for the central nervous system without reliance on glucose production from ingested protein or fat."
Carbohydrates are the sources of energy that start with glucose, the sugar in your bloodstream that is one sugar molecule, and include substances containing many sugar molecules called complex carbohydrates, starches, cellulose, and gums. Some of the common sources of carbohydrate are bread, potatoes, grains, cereals, and rice.
Physicians know a lot of information about carbohydrate in the body:
Carbohydrate is the primary source of energy for muscles.
Glucose is the carbohydrate that causes the pancreas to release insulin.
Carbohydrate causes the triglyceride (fat) level to rise in the blood.
When insulin is not present or is ineffective, more carbohydrate raises the blood glucose higher.
Because carbohydrate is the food that raises the blood glucose, which is responsible for the complications of diabetes, it seems right to recommend a diet that is lower in carbohydrate than previously suggested. Furthermore, a major source of coronary artery disease in diabetes is metabolic syndrome. Because increased carbohydrate triggers increased triglyceride, which is the beginning of a number of abnormalities that lead to increased coronary artery disease, recommending less carbohydrate on this basis as well seems prudent.
Glycemic index
All carbohydrates are not alike in the degree to which they raise the blood glucose. This fact was recognized some years ago, and a measurement called the glycemic index was created to quantify it. The glycemic index (GI) uses white bread as the indicator food and assigns it a value of 100. Another carbohydrate of equal calories is compared to white bread in its ability to raise the blood glucose and is assigned a value in comparison to white bread. A food that raises glucose half as much as white bread has a GI of 50, whereas a food that raises glucose 1-1/2 times as much has a GI of 150.
The point is to select carbohydrates with low GI levels to try to keep the glucose response as low as possible. A glycemic index of 70 or more is high, 56 to 69 is medium, and 55 or less is low.
Good clinical studies have shown that knowledge of the glycemic index of food sources can be very valuable. Evaluation of the diet of people who develop diabetes compared with those who don't shows that, all other things being equal, the people with the highest GI diet most often develop diabetes. After diabetes is present, patients who eat the lowest GI carbohydrates have the lowest levels of blood glucose. Patients in these studies have not had great difficulty changing to a low GI diet. The other thing that happens when low GI food is incorporated into a diet is that the levels of triglycerides and LDL (or "bad" cholesterol) fall in both type 1 and type 2 diabetes.
Switching to low GI carbohydrates can be very beneficial for controlling the glucose. You can easily make some simple substitutions in your diet, as shown in the following table.
| High-GI Food | Low-GI Food |
|---|---|
| White bread | Whole-grain bread |
| Processed breakfast cereal | Unrefined cereals like oats and processed low-GI cereals |
| Plain cookies and crackers | Cookies made with dried fruits or whole grains like oats |
| Cakes and muffins | Cakes and muffins made with fruit or whole grains like oats |
| Tropical fruits like bananas | Temperate-climate fruits like apples and plums |
| Potatoes | Pasta and legumes |
| White rice | Basmati and other low-GI rice |
Because bread and breakfast cereals are major daily sources of carbohydrates, these simple changes can make a major difference in lowering your glycemic index. Foods that are excellent sources of carbohydrate but have a low GI include legumes such as peas or beans, pasta, grains like barley, parboiled rice (rice that is partially boiled in the husk, making it nutritionally similar to brown rice), bulgur, and whole-grain breads.
Even though a food has a low GI, it may not be appropriate because it is too high in fat. You need to evaluate each food's fat content before assuming that all low GI foods are good for a person with diabetes.
And though a food has a high GI, it may still be acceptable in your diet if it contains very little total carbohydrate. For example, cantaloupe has a GI of about 70, but the amount of total carbohydrate is so low that it doesn't raise your blood glucose significantly when you eat a normal portion. This concept is called the glycemic load (GL), a number that takes both glycemic index and total carbohydrates into account. A GL of 20 is high, 11 to 19 is medium, and 10 or less is low.
If you want to go into this subject in deeper detail, you can find a listing of many foods by category of food and by level of GI, portion size, and GL on the web at www.glycemicindex.com.
Fiber
Fiber is the part of the carbohydrate that is not digestible and, therefore, adds no calories. Fiber is found in most fruits, grains, and vegetables. Fiber comes in two forms:
Soluble fiber: This form of fiber can dissolve in water and has a lowering effect on blood glucose and fat levels, particularly cholesterol.
Insoluble fiber: This form of fiber cannot dissolve in water and remains in the intestine. It absorbs water and stimulates movement in the intestine. Insoluble fiber also helps prevent constipation and possibly colon cancer. This fiber is called bulk or roughage.
Before the current trend to refine foods, people ate many sources of carbohydrate that were high in fiber. These sources were all plant foods such as fruits, vegetables, and grains. Animal foods contain no fiber.
Because too much fiber causes diarrhea and gas, you need to increase the fiber level in your diet fairly slowly. The recommendation for daily fiber is 20 to 30 grams. Most Americans eat only about 15 grams daily.
Many of the foods listed in the previous section as having a low glycemic index contain a lot of fiber, which helps to reduce the blood glucose.
The way to eat the right amount of carbohydrate without increasing your blood glucose or triglycerides is to make it a low-glycemic, high-fiber carbohydrate. Such a diet has been shown to reduce the need for insulin in women with gestational diabetes without any negative effect on the fetus or mother. Increased dietary fiber intake has been shown to reduce the risk of death, not only from heart and blood vessel disease but also from infectious respiratory diseases.