Compared to fats and protein, carbohydrates have the greatest impact on blood sugar (glucose). There are three main types of carbohydrates: sugars, starches, and fiber. Dietary fiber is not digestible. Sugars and starches are eventually broken down by the body into glucose.
Starches are broken down more slowly by the body than sugars. Some foods that are high in starch content are more likely to provide other nutritional components, as well as fiber:
- Vegetables, fruits, whole grains, beans, and dairy products are good sources of carbohydrates.
- Whole grain foods such as brown rice, quinoa, bulgur, farro, oatmeal, and whole-wheat bread (when you can see the seeds and whole grains), provide more nutritional value than pasta, white rice, white bread, and white potatoes.
Fiber is an important component of many plant-based foods. There are two types of fiber:
- Soluble fiber attracts water and turns to gel during digestion. This slows digestion. Soluble fiber is found in oat bran, barley, nuts, seeds, beans, lentils, peas, and some fruits and vegetables. It is also found in psyllium, a common fiber supplement. Some types of soluble fiber may help lower cholesterol, but the effect on heart disease is not known.
- Insoluble fiber is found in foods such as wheat bran, vegetables, and whole grains. It adds bulk to the stool and appears to help food pass more quickly through the intestines.
Sugars add calories, increase blood glucose levels quickly, and provide little or no other nutrients:
- Sucrose (table sugar) is the source of most dietary sugar, found in sugar cane, honey, and corn syrup.
- Fructose, the sugar found in fruits, produces a smaller increase in blood sugar than sucrose. The modest amounts of fructose in fruit can be handled by the liver without significantly increasing blood sugar, but the large amounts in soda and other processed foods with high-fructose corn syrup overwhelm normal liver mechanisms and trigger production of unhealthy triglyceride fats.
- A third sugar, lactose, is a naturally occurring sugar found in dairy products including yogurt and cheese.
People with diabetes should avoid products listing more than 5 grams of sugar per serving, and some providers recommend limiting fruit intake. Although moderation is important, fruits are an important part of any diet. They provide essential vitamins, minerals, and antioxidants, as well as fiber. You can limit your fructose intake by consuming fruits that are relatively lower in fructose (cantaloupe, grapefruit, strawberries, peaches, bananas) and avoiding added sugars such as those in sugar-sweetened beverages. Fructose is metabolized differently than other sugars and can significantly raise triglycerides, though usually a large intake of fructose is needed to do this (or drinking fructose sweetened beverages with a meal).
In addition, limit processed foods with added sugars of any kind. Pay attention to ingredients in food labels that indicate the presence of added sugars. These include terms such as sweeteners, syrups, fruit juice concentrates, molasses, and sugar molecules ending in "ose" (like dextrose and sucrose).
Artificial sweeteners use chemicals that mimic the sweetness of sugar. They include aspartame (NutraSweet, Equal), sucralose (Splenda), saccharin (Sweet'N Low), and rebiana (Truvia). (Rebiana is an extract derived from the plant stevia.) These products do not contain calories and do not affect blood sugar. Artificial sweeteners can help with weight control, but it is important not to consume extra calories elsewhere. Artificial sweeteners have become more controversial in the past few years. Consumption of some artificial sweeteners is even associated with weight gain.
The Carbohydrate Counting System
Some people plan their carbohydrate intake using a system called carbohydrate counting. It is based on these premises:
- All carbohydrates (either from sugars or starches) will raise blood sugar to a similar degree based on the weight, although the rate at which blood sugar rises depends on the type of carbohydrate and on the individual. A higher peak won't last as long while a lower peak may take longer to return to premeal blood sugar levels, but the total area under the curve for the increase in blood sugar will be similar.
- Carbohydrates have the greatest impact on blood sugar. Fats and protein play only minor roles.
- Carbohydrate counting is very important for people with type 1 diabetes and anyone on an insulin regimen. Carbohydrate counting can even help control blood glucose levels in people with type 2 diabetes who are not on insulin regimens.
The basic goal of carbohydrate counting is to balance insulin with the amount of carbohydrates eaten in order to control blood sugar (glucose) levels after a meal. There are several options for counting carbohydrates. It's best to work with an RD.
A dietitian can create a meal plan that accommodates the person's weight and needs. Many people with type 1 diabetes work with their providers to determine a carbohydrate to insulin ratio. This special calculation tells the person how much insulin they need to take to cover a certain amount of carbohydrate in the meal. A common ratio would be 1 unit of insulin for 15 grams of carbohydrate. Then if you choose a meal with 60 grams of carbohydrate you know you need 4 units of insulin to match the carbohydrates and prevent the meal from increasing your blood sugar level. When people learn how to count carbohydrates and adjust insulin doses to their meals, many find this system more flexible, more accurate in predicting blood sugar increases, and easier to plan meals than other systems.
The Glycemic Index
The glycemic index helps determine which carbohydrate-containing foods raise blood glucose levels more or less quickly after a meal. The index uses a set of numbers for specific foods that reflect greatest to least delay in producing an increase in blood sugar after a meal. The lower the index number, the better the impact on glucose levels. This system is artificial in that the number is calculated when eating only that food. The index for mashed potato is 72, but eating the same amount of mashed potato with gravy, green beans and grilled chicken breast would change the absorption time significantly. The index also does not account for variation in food preparation. The lower (good) glycemic index of brown rice can be increased (bad) just by increasing the cooking time. The index also does not account for mixed meals. For example, eating white rice with a sauce that includes chicken, vegetables and coconut milk will change the glycemic index vs. eating white rice alone.
There are two indices in use. One uses a scale of 1 to 100 with 100 representing a glucose tablet, which has the most rapid effect on blood sugar. [See Table: "The Glycemic Index of Some Foods," below.] The other common index uses a scale with 100 representing white bread (so some foods will be above 100).
Choosing foods with low glycemic index scores may have a modest effect on controlling the surge in blood sugar after meals. Substituting low- for high-glycemic index foods may also help with weight control.
One easy way to improve glycemic index is to simply replace starches and sugars with whole grains and legumes (dried peas, beans, and lentils). However, there are many factors that affect the glycemic index of foods, and maintaining a diet with low glycemic load is not straightforward.
No one should use the glycemic index as a complete dietary guide, since it does not provide nutritional guidelines for all foods. It is simply an indication of how the body will respond to certain carbohydrates.
The Glycemic Index of Some Foods
Based on 100 = a Glucose Tablet
Kidney (dried and boiled, not canned)
Spaghetti (boiled 5 minutes)
Spaghetti (boiled 15 minutes)
Note. These numbers are general values, but they may vary widely depending on other factors, including if and how they are cooked and foods they are combined with.
Low-carbohydrate diets generally restrict the amount of carbohydrates but do not restrict protein and fat sources. The larger variation usually becomes the fat content as the percent of calories from protein does not vary as much between diets:
- Low-carbohydrate diets are mostly fairly similar (such as Paleo, South Beach, Atkins, Sugar Busters.)
- While initial phases and instructions vary, the majority of the caloric reduction comes from eliminating the big starches (rice, bread, pasta, potato, flour).
- Although there have been concerns that these diets may be harmful for bone and kidney health, good scientific studies have not shown evidence of these effects.
- Many of these diets make other claims related to hunger, satiety, exercise tolerance, energy, and immune system function, but none of these claims have been proven by any scientific studies.
- All of these diets work by reducing the number of calories you are eating rather than through any of the many claims of special properties related to the diet itself or the supplements that you may be asked to purchase.
- These diets fail as soon as the diet is liberalized and people start adding low-carbohydrate cookies, chips, and bread back to their diet thereby increasing their caloric intake.
- The Mediterranean diet is a heart-healthy diet that is rich in vegetables, fruits, and whole grains as well as healthy monounsaturated fats such as olive oil. It restricts saturated fat proteins like red meat. Studies on the Mediterranean diet are difficult to interpret, as the definition of the diet itself may vary. However, in studies of people with type 2 diabetes, a low carbohydrate version of the diet (restricting carbohydrates to less than 50% of total calories) worked better than a low-fat diet in promoting weight loss, reducing A1C levels, and improving insulin sensitivity and glycemic control.
Protein is important for strong muscles and bones. Eating protein may help people feel full sooner and longer and thus reduces overall calories. In addition, protein consumption helps the body maintain lean body mass during weight loss. However, some types of protein (red meat, full-fat dairy products) are high in saturated fat, which can be bad for the heart and can make weight gain more likely.
Good sources of protein include fish, skinless chicken or turkey, low-fat dairy products, soy (tofu), and legumes (such as kidney beans, black beans, chickpeas, and lentils).
Legumes are one of the healthiest types of foods and are an important source of protein for vegetarians. Legumes include all sorts of beans such as black beans, pinto beans, lentils, and chickpeas. Dried beans can take more time to prepare, but they have less sodium (salt) than canned varieties. You can also reduce sodium by draining and rinsing canned products.
Soy protein is found in products such as tofu, soy milk, and soybeans. (Soy sauce is not a good source. It contains only a trace amount of soy and is very high in sodium.)
Plant-based proteins are rich in both soluble and insoluble fiber, and have more vitamins and minerals than meat or dairy proteins. They are also low in fat.
Fish is one of the best sources of protein. Evidence suggests that eating moderate amounts of fish (twice a week) may improve triglycerides and help lower the risks for death from heart disease. The healthiest fish are oily fish such as salmon, mackerel, or sardines, which are high in omega-3 fatty acids.
The omega-3 fatty acids contained in fish oil are also available as dietary supplements. However, according to the American Diabetes Association, there is no evidence that shows these supplements help prevent or treat diabetes. Eating fish is a better way to get omega-3 fatty acids.
Meat and Poultry
Lean cuts of meat are the best choice for heart health and diabetes control. Saturated fat in meat is the primary danger to the heart. The fat content of meat varies depending on the type and cut. Skinless chicken or turkey, which are lower in saturated fat, are better choices than red meat. (Fish is an even better choice.)
A high intake of dairy products may lower risk factors related to type 2 diabetes and heart disease (insulin resistance, high blood pressure, obesity, and unhealthy cholesterol). Some research suggests the calcium in dairy products may be partially responsible for these benefits. Vitamin D contained in dairy may also play a role in improving insulin sensitivity, particularly for children and adolescents. However, because many dairy products are high in saturated fats and calories, it's best to choose low-fat and nonfat dairy items. Some nonfat items have a lot of added sugar - check the label!
Fats can have good or bad effects on health, depending on their chemistry. The type of fat appears to be more important than the total amount of fat when it comes to reducing heart disease, but all fats should be consumed in moderation. All fats, good or bad, are high in calories compared to proteins and carbohydrates. One fat gram provides 9 calories.
Current dietary guidelines for diabetes and heart health recommend that:
- Monounsaturated fatty acids (found in olive oil, canola oil, peanut oil, nuts, and avocados) and omega-3 polyunsaturated fatty acids (found in fish, shellfish, flaxseed, and walnuts) should be the first choice for fats.
- Omega-6 polyunsaturated fatty acids (corn, safflower, sunflower, and soybean oils and nuts and seeds) are the second choice for fats.
- Limit saturated fat (found predominantly in animal products, including meat and full fat dairy products, as well as coconut and palm oils) to less than 7% of total daily calories.
- Avoid trans fats (found in margarine, commercial baked goods, snacks, and fried foods). Trans fats are listed on nutrition facts food labels. Even if 0 trans fats are listed, look at the list of ingredients for words like hydrogenated oil or partially hydrogenated oil. Avoid foods that have a liquid oil listed first on the ingredients list.
Try to replace saturated fats and trans fatty acids with unsaturated fats from plant and fish oils. Omega-3 fatty acids, which are found in fish and a few plant sources, are a good source of unsaturated fats. Fish oils contain the omega-3 fatty acids docosahexaenoic (DHA) and eicosapentanoic (EPA) acids, which have significant benefits for the heart. Generally, 2 servings of fish per week provide a healthful amount of these omega-3 fatty acids.
Dietary Cholesterol and Plant Sterols
Animal-based foods contain cholesterol, which contributes to heart disease. (However, saturated fat has a much greater impact on cholesterol levels than dietary cholesterol.) High amounts of cholesterol occur in meat, dairy products, and shellfish. Although egg yolks contain cholesterol, up to 2 eggs (whole eggs) per day can be healthful for most people and are a good source of protein, iron, and B vitamins.
Plant foods, such as fruits, vegetables, nuts, and grains, do not contain cholesterol. Plant substances known as sterols, and their derivatives called stanols, may reduce cholesterol by blocking its absorption in the intestinal tract. Margarines containing sterols are available.
Sodium (Salt) and Potassium
It is important for everyone to restrict their sodium (salt) intake. People with diabetes should reduce sodium intake to no more than 2,300 mg daily (less than 1 teaspoon of salt). Some people may benefit from restricting sodium intake to no more than 1,500 mg per day. Limiting or avoiding consumption of processed foods can go a long way to reducing salt intake. Simply eliminating table and cooking salt is also beneficial. The DASH diet is an excellent heart-healthy eating plan that restricts sodium.
Salt substitutes, such as Nu-Salt and Mrs. Dash (which contain mixtures of potassium, sodium, and magnesium) are available, but they can be risky for people with kidney disease or those who take blood pressure medication that causes potassium retention.
Potassium-rich foods are also important for good blood pressure. The best source of potassium is from the fruits and vegetables that contain them. Potassium-rich foods include bananas, oranges, pears, prunes, cantaloupes, tomatoes, dried peas and beans, nuts, potatoes, and avocados.
People with diabetes should check with their providers before increasing the amount of potassium in their diets. Eating too many potassium-rich foods can cause problems for some people. (No one should take potassium supplements without consulting a provider.) Kidney problems can cause potassium overload, and medications commonly used in diabetes (such as ACE inhibitors or potassium-sparing diuretics) also limit the kidney's ability to excrete potassium.
Alcohol and Coffee
The American Diabetes Association recommends limiting alcoholic beverages to 1 drink per day for non-pregnant adult women and 2 drinks per day for adult men. Excess alcohol intake can increase the risk of both high (hyperglycemia) and low (hypoglycemia) blood sugar.
Many studies have noted an association between coffee consumption (both caffeinated and decaffeinated) and reduced risk for developing type 2 diabetes. Researchers are still not certain if coffee protects against diabetes. (If you drink coffee, don't add sugar or creamers, which negate any possible benefits.)
Research has shown that vitamin supplements have no benefit for heart disease or diabetes. Because of the lack of scientific evidence for benefit, the American Diabetes Association does not recommend regular use of vitamin or mineral supplements, except for people who have nutritional deficiencies.
People with type 2 diabetes who take metformin (Glucophage, generic) should be aware that this drug can interfere with vitamin B12 absorption. Calcium supplements may help counteract metformin-associated vitamin B12 deficiency.
Generally, manufacturers of herbal remedies and dietary supplements do not need FDA approval to sell their products. Just like a drug, herbs and supplements can affect the body's chemistry, and therefore have the potential to produce side effects that may be harmful. There have been a number of reported cases of serious and even lethal side effects from herbal products. People should always check with their providers before using any herbal remedies or dietary supplements.
Traditional herbal remedies for diabetes include bitter melon, cinnamon, fenugreek, and Gymnema sylvestre. Few well-designed studies have examined these herbs' effects on blood sugar, and there is not enough evidence to recommend them for prevention or treatment of diabetes.
Various fraudulent products are often sold on the Internet as "cures" or treatments for diabetes. These dietary supplements have not been studied or approved. The FDA warns people with diabetes not to be duped by bogus and unproven remedies.