The term diabetes mellitus refers to a group of diseases that result in higher than normal amounts of sugar (glucose) in the bloodstream.
Diabetes occurs as a result of deficiency or insufficient action of insulin, a hormone that helps glucose to enter cells. In type 1 diabetes, the insulin-producing cells of the pancreas are destroyed, resulting in a complete absence of insulin. In type 2 diabetes, the pancreas is able to produce insulin, at least initially, but the cells of the body resist insulin's action, causing the body to need to produce extra insulin in order to get glucose into cells. When the pancreas can no longer produce enough insulin to maintain normal blood glucose levels, diabetes is diagnosed.
Diabetes can result in many complications, including heart disease, eye problems, kidney failure, nerve symptoms, leg amputation, and others. See the Diabetes Complications chapter for more information on these.
There are three major types of diabetes mellitus:
- Type 1 diabetes, accounting for approximately 5 to 10 percent of all cases, occurs as a result of destruction of the insulin-producing cells of the pancreas. Most cases begin in childhood with symptoms of unexplained weight loss, fatigue, excessive thirst and urination, and blurred vision. Less commonly, it can also be diagnosed in adults. Type 1 diabetes requires insulin treatment.
- Type 2 diabetes, which accounts for roughly 90 percent of diabetes cases, is often associated with excess weight. Most cases occur in adults, but the occurrence is climbing rapidly in children, due to increasing rates of childhood obesity. Type 2 diabetes is often accompanied by hypertension and high cholesterol. Although some patients with type 2 diabetes require insulin injections, most are treated with oral medications. Symptoms tend to be much milder in type 2 than in type 1 when the disease first presents, but complications of type 2 diabetes are frequent and can be life-threatening.
- Gestational diabetes mellitus accounts for about 2 percent of diabetes cases. As its name suggests, gestational diabetes first appears during pregnancy. Hormones secreted by the placenta-estrogen, progesterone, growth hormone, corticotrophin-releasing hormone, and prolactin-decrease the function of insulin, resulting in high blood sugar. Treatment with dietary changes and/or drugs (usually insulin) is essential to prevent fetal complications. Although blood sugar levels usually normalize after birth, many women with gestational diabetes eventually develop type 2 diabetes.
Risk factors for type 1 diabetes include:
- Family history: When a first-degree relative has diabetes, the risk of developing type 1 diabetes is about 10 to 15 percent. Many possible genes are under investigation.
- Exposure to cow's milk proteins: Consumption of cow's milk in early childhood has been under investigation as a contributing factor.
- Fetal or childhood viral infections
- Birth weight greater than 9.9 pounds
- Preeclampsia (high maternal blood pressure during mother's pregnancy)
- Being born to a mother older than 25
Risk factors for type 2 diabetes include:
- Family history of type 2 diabetes in first- or second-degree relatives
- Older age
- Abdominal obesity
- History of gestational diabetes
- The presence of hypertension and high cholesterol
- Race and Ethnicity: African-Americans, Latinos, American Indian/Alaska Natives, and Asians and Pacific Islanders have a greater risk.
Risk factors for gestational diabetes are listed below. In addition, individuals of Asian, African, Native-American, and Hispanic ancestry have greater risk for gestational diabetes than non-Hispanic whites. The risk factors for gestational diabetes overlap with type 2 diabetes.
- Family history of type 2 diabetes in a first-degree relative
- History of high blood sugar
- Steroid use during pregnancy
- Polycystic ovarian syndrome
- Age greater than 25 years
- A pre-pregnancy weight at least 10 percent above ideal body weight
- Previous child with birth weight greater than 9 pounds
- Maternal birth weight greater than 9 pounds or less than 6 pounds
Diabetes Mellitus: Diagnosis and Treatment
- The examination begins with a medical history and a physical examination.
- Blood glucose testing will be performed. Testing may be done either randomly, fasting, or as part of a glucose tolerance test, which measures blood glucose after the patient has ingested a sugary test syrup.
- In patients with diabetes, a blood test for hemoglobin A1c levels can be used to follow the adequacy of blood sugar control. It provides a fairly accurate measurement of the average blood sugar during the previous two to three months. Risk of complications is lower in patients who maintain lower A1c values.
- In some patients, type 1 diabetes can be confirmed by blood tests that identify antibodies directed against the pancreas. However, there are no tests for type 2 diabetes beyond measurement of blood sugar.
- Screening for gestational diabetes is a routine part of prenatal examinations. Screening typically occurs between 24 and 28 weeks of gestation and involves a similar blood sugar test as with the other types of diabetes.
Dietary and lifestyle interventions are important for patients with all types of diabetes mellitus (see Nutritional Considerations). Education for diabetes self-management, which includes self-monitoring of blood sugar, is an important component of treatment.
For all types of diabetes, good blood sugar control decreases the risk of complications. It is important to be aware that certain medications (e.g., beta-blockers, steroids, thiazides diuretics, and oral contraceptives) can cause high blood sugar.
Type 1 Diabetes
Type 1 diabetes requires treatment with insulin injections. Insulin is available in several forms:
- Long-acting insulin can be administered once daily.
- Regular insulin or fast-acting insulin are quick-acting and can be administered before meals to curb the blood sugar elevations that occur after large meals.
- Fast-acting, inhalable insulin was approved for use in adults in 2006. However, its long-term safety remains unclear.
- Pramlinitide may also be injected at mealtimes along with fast-acting insulin. It reduces the elevations in blood sugar that occur with meals and suppresses appetite, which may lead to weight loss.
Type 2 Diabetes
There is a menu of medication options available to treat type 2 diabetes. Some people will require insulin, but it is common, especially in the early years following the diagnosis, to use one or more oral medications. The choice is based on factors such as effectiveness, expense, and other health problems that may be improved or worsened by one medication or another. It is important to know the name, dose, action, and possible side effects of any pills that have been prescribed. Below is a brief summary, with costs based on an online pharmacy search. Consult your pharmacist or your health care provider for more information.
The most commonly used oral medication is metformin (Glucophage). This pill works primarily by decreasing the liver's production of glucose. Common side effects are stomach cramps, loose stool, and flatulance, but these often go away over time. This drug should not be used by people who have liver or kidney problems, both of which can be checked with simple blood tests. It also should not be used in people over 80 years of age, those who have any heart failure, or those who use alcohol. Metformin by itself will not generally cause blood sugar levels to get too low, and it works as something of an appetite suppressant. The average cost is about $60/month.
The largest and oldest group of drugs for diabetes work by helping the pancreas to make more insulin. Some common examples include glipizide (Glucotrol), glyburide (Diabeta, Micronase, or Glynase), and glimepride (Amaryl). The pills should be taken at lower doses in those with kidney problems and should generally not be used by people who are allergic to sulfa. The most common side effect is low blood sugar, which can sometimes cause people to feel hungry and eat more, which can cause weight gain. Another problem with these pills is that, for most people, they stop working after a few years. In some people, they can increase the risk of sunburn. The prices can range from $10 to $110/month.
Two more recent additions also help the pancreas to make more insulin. These are nateglinide (Starlix) and repaglinide (Prandin). These only last a few hours, so they must be taken before each meal. These pills may cause low blood sugar, but are less likely to do so than some other medications because they last for such a short time. They work best early in the disease process. The cost can range from $130 to $230/month.
Some medications work to by slowing down the digestion of carbohydrate. These include acarbose (Precose) and miglitol (Glyset). These must be taken with the first bite of food at each meal. They commonly cause abdominal pain, diarrhea, and flatulence. Low blood sugar can occur, and if does, it must be treated with pure glucose tablets or gel, or milk with lactose, since the medication blocks other carbohydrates, such as juice. The cost is around $110 to $160/month.
Another group of medications makes the muscle cells less resistant to insulin. These include pioglitazone (Actos) and rosiglitazone (Avandia). These pills should not be used in anyone with an abnormal liver function blood test or a history of heart failure. By themselves, these pills will not usually cause low blood sugar, but they do tend to cause weight gain and fluid retention. They cost around $170/month.
One of the newest types of medications for diabetes works to enhance the body's incretin system, which helps to regulate blood sugar levels. The only drug is this class so far is sitagliptin (Januvia). It works best early in the diagnosis, and does not cause low blood sugar or weight gain. However, it costs about $150/month.
If the medication you take is one of the ones that can cause low blood sugar, you should be aware of the signs and symptoms, and be prepared to treat it if it occurs. If blood sugar levels get too low (usually below 80, or whatever your health care provider feels is too low for you), you may feel the way you would if you went too long without eating. You might develop a headache or feel irritable or anxious. Other common symptoms are dizziness, sweating, shaking, and/or a change in vision. If left untreated, blood sugar may continue to drop, and can cause slowed reflexes, unsteadiness, and possibly loss of consciousness.
Low blood sugar can occur from certain diabetes medications if you go too long without eating, or eat less than usual, or if you are significantly more active than usual. It is important to know if the medication you take for diabetes can cause low blood sugar. If so, be sure to always carry a treatment, such as a small juice box, or three to four glucose tablets, or a roll of Lifesavers. These will help to quickly bring your blood sugar level back up to normal, but will not last very long, so have a snack or a meal within 30 minutes of a low blood sugar event to prevent it from happening again.
As you change to a healthy, low-fat, plant-based diet, those medications may become too strong and you may start to have some of the symptoms of low blood sugar described above. This does not mean the diet is bad! This may be a sign that you no longer need as much medication.
Talk to your health care provider about your medication(s) if you experience low blood sugar.
Dietary changes are the first-line treatment (see Nutritional Considerations). If dietary changes are not sufficient to achieve normal blood sugar, insulin injections should be considered.
Role of Exercise
A sedentary lifestyle is associated with increased risk for high blood sugar and diabetes. In persons with established diabetes, exercise reduces blood sugar levels. Exercise also reduces cardiovascular complications of diabetes, including high blood pressure, heart disease, and inflammation. Exercise alone has little or no effect on body weight.
Women who either have or are at risk for gestational diabetes can also benefit from exercise. Walking or upper-body exercises (but never while lying on the back) may reduce the risk of gestational diabetes and help lower blood sugar levels to the normal range. In women with gestational diabetes, exercise has been found to be a useful strategy for helping to maintain blood sugar within the normal range, and for helping these women to control blood sugar without the use of insulin. However, exercising must be stopped if contractions occur.
Diabetes Mellitus: Nutritional Considerations
Prevention: Type 1 Diabetes
Dietary factors that may influence the risk of type 1 diabetes have been under investigation. The following considerations have emerged as potentially important candidates for preventive strategies:
- Breast-feeding: In some epidemiologic studies, breast-feeding is associated with reduced risk of developing type 1 diabetes. Longer duration of breast-feeding may be the key to reduced risk, presumably by increasing protection against infections, enhancing the infant's immune responses, and delaying exposure to foreign food allergens. Although breast-feeding is the best choice for infant feeding, controlled trials of its effect on diabetes risk are difficult from ethical and practical standpoints and have not been conducted.
- Avoidance of early introduction of cow's milk: Cow's milk has been related to the diagnosis of diabetes, and children with type 1 diabetes have been found to have higher levels of antibodies against certain proteins contained in cow's milk. Although it has not yet been proven conclusively that cow's milk is a trigger for type 1 diabetes, the American Academy of Pediatrics concluded that avoiding early exposure to cow's milk may reduce the risk. An international study, the Trial to Reduce Type 1 Diabetes in the Genetically at Risk (TRIGR) study, has been designed to test the hypothesis that using a hydrolyzed formula instead of cow's milk may delay or prevent the onset of type 1 diabetes in genetically susceptible children. Although the results of this study are pending, a smaller study with a similar design found that this intervention resulted in a significant protection from diabetes.
- Avoiding early introduction of gluten-containing foods: A higher prevalence of celiac disease has been observed in children with type 1 diabetes, compared with other children. In epidemiologic studies, supplementing infant diets with gluten-containing foods (e.g., wheat, barley, and rye) before the age of three months is associated with increased risk for developing antibodies typical of diabetes. In some children, both early (before three months) and late (after seven months) introduction of cereals was associated with increased risk.
Prevention: Type 2 Diabetes
Although type 2 diabetes has a strong genetic component, diet and lifestyle significantly affect the likelihood that the disease will occur. The risk for type 2 and gestational diabetes can be decreased by maintaining a healthy weight and a healthful diet.
Individuals in Asia and Africa who follow traditional diets low in animal fat and high in complex carbohydrates have a far lower prevalence of diabetes than those who follow a Western diet. Vegetarians also have a lower prevalence of diabetes than meatâ€“eaters.
These results are probably due to several factors. Intake of saturated fat is associated with high blood sugar, poor insulin action, gestational diabetes, and type 2 diabetes. In contrast, a higher intake of dietary fiber, particularly in the form of fruits and vegetables, results in lower blood sugar levels following meals. In addition, high-fiber diets often contain micronutrients important in regulation of blood sugar, including magnesium and vitamin E.
The Diabetes Prevention Program (DPP) demonstrated that dietary changes designed to reduce body weight, combined with regular exercise, can significantly reduce the risk for type 2 diabetes. Specifically, risk was reduced by nearly 60 percent in the group that combined diet and exercise, compared with a 30 percent reduction for those on drug treatment. In individuals age 60 and older, the risk was reduced more than 70 percent with diet and exercise, while drug treatment was not effective for persons older than 45 years.
Nutritional Management of Diabetes
The goals of nutrition therapy in diabetes management include control of blood sugar at near-normal levels, maintenance of healthy blood pressure and cholesterol levels, and attainment of a healthy weight. Adherence to a healthful diet, regular exercise, and use of medications when necessary may achieve these goals and help minimize the risk of complications.
- Maintenance a healthy weight: Current guidelines of the American Diabetes Association prescribe a calorie-controlled meal plan that uses food exchange lists that keep carbohydrate intake reasonably steady throughout the day and from one day to the next. The guidelines also limit saturated fat and cholesterol. Advantages of this approach include flexibility and the allowance of most foods, albeit in limited amounts. Its disadvantages include the need to measure foods and the difficulty in restricting calories over the long term. Such diets require ongoing education and monitoring, which should generally be provided by a registered dietitian in a series of visits.
Recent studies suggest that low-fat, plant-based diets may be more effective for weight loss, blood sugar control, and reduction of cardiovascular risk factors, particularly blood cholesterol. Such diets may also be easier for patients to follow. A low-fat, plant-based diet works in several ways. First, because such diets are low in fat, they tend to be low in calories. And because they are high in fiber, they are filling. The result is a low calorie intake and easy weight loss, an important effect given that increased body fat is associated with diabetes. A recent study showed that a low-fat, vegan diet led to greater weight loss and blood glucose control, compared to a diet following American Diabetes Association guidelines.
- Carbohydrate type may influence blood sugar control: A review of five studies of individuals with type 1 or type 2 diabetes showed that diets with fewer simple sugars improved glucose control. Furthermore, diets richer in fiber tend to produce lower blood sugar levels after meals, compared with fiber-depleted diets, and high-fiber diets have been shown to improve control of blood sugar in individuals with type 2 diabetes. Because vegan diets consist solely of plant-derived foods, they are typically high in fiber, compared with non-vegan diets, provided the diet does not rely heavily on processed foods.
The glycemic index is a means of rating the effect of various foods on blood glucose. High-glycemic-index foods tend to raise blood sugar rapidly. These include sugar, wheat breads, baking potatoes, and most cold cereals. Low-glycemic-index foods tend to have less effect on blood sugar. These include beans, rye or pumpernickel bread, yams, sweet potatoes, oatmeal, bran cereals, and most vegetables and fruits. Favoring low-glycemic-index foods may help control blood glucose and may also reduce triglycerides (blood fats).
- Excess body iron stores may increase the risk for diabetes: Limited evidence suggests that elevated body iron stores are associated with diabetes, and lowering the excess iron (by dietary changes or blood donation) may decrease the risk. A study comparing 30 vegetarians and 30 meat-eaters, all of whom were healthy and had normal body weights, showed that the vegetarians had adequate, but lower, body iron stores, compared with the meat-eaters. The vegetarians also demonstrated less risk for diabetes than the meat-eaters.
Similar dietary changes are helpful for patients with type 1 diabetes. A high-fiber diet results in lower insulin requirements and improved management of blood sugar and cholesterol.
Further study is needed to establish optimal dietary interventions in gestational diabetes. Some evidence suggests that a diet limiting carbohydrates to 40 percent of calories, with fat providing 40 percent and protein providing the remaining 20 percent, improves control of blood sugar and reduces the need for insulin injections. Future studies are required to compare a carbohydrate-reduced diet with a low-fat, high-fiber diet, particularly a vegan diet.
Vegan diets may present a clinical advantage because they include no animal fat, and increases in food quantity are less likely to result in substantial increases in saturated fat intake. While vegetarian or vegan diets may sound restrictive at first glance, their acceptability in clinical studies is similar to that of other types of diets. Because vegan diets do not limit portions, calories, or carbohydrates, they may be simpler to follow than regimens that limit quantities of certain foods.
Dietary Supplements in Type 2 Diabetes
Several supplements have been investigated for their role in diabetes management, notably chromium and certain botanicals:
- Chromium: Chromium is believed to increase the body's response to insulin. However, studies in individuals with type 1, type 2, or gestational diabetes, including trials using daily doses as high as 1,000 mcg of chromium, have yielded mixed results. Thus, most diabetes authorities do not recommend chromium supplements.
According to the Food and Nutrition Board of the Institute of Medicine, the safe and adequate daily intakes of chromium for adults 19 to 50 years of age are 35 mcg for men and 25 mcg for women. For people over 50, the numbers are 30 mcg for men and 20 mcg for women. Most common multiple vitamins include chromium, usually in amounts ranging from 100 to 200 mcg.
- Botanicals: The role of certain botanicals for patients with type 2 diabetes is also under investigation. Metformin, a common diabetes drug, was developed from Galega officinalis (French lilac). Ginseng has been found in small studies to lower blood sugar levels after large meals. Bitter melon (Momordica charantia), a botanical with insulin-like effects, has also demonstrated blood sugar-lowering effects in humans.
In spite of these initial benefits, problems remain with the use of botanicals in diabetes. First, clinical trials of ginseng and bitter melon have included only small numbers of persons, yielding inconclusive results. Another problem is the lack of standardization of active ingredients.