The relationship between eating carbohydrates and type 2 diabetes is complex. While eating carbohydrates increases the need for insulin to keep blood sugar normal, diets high in total carbohydrates do not necessarily increase the risk of type 2 diabetes. Researchers have found that diets very high in sugar may worsen glucose tolerance in nondiabetic animals and humans. However, the amount of sugar used in these studies in proportion to other foods was much larger than is typically found in human diets.
Eating carbohydrate-containing foods, whether high in sugar or high in starch (such as bread, potatoes, processed breakfast cereals, and rice), temporarily raises blood sugar and insulin levels. The blood sugar–raising effect of a food, called its “glycemic index,” depends on how rapidly its carbohydrate is absorbed. Many starchy foods have a glycemic index similar to table sugar (sucrose). People eating large amounts of foods with high glycemic indexes have been reported to be at increased risk of type 2 diabetes. On the other hand, eating a diet high in carbohydrate-rich foods with low glycemic indexes is associated with a low risk of type 2 diabetes. Beans, peas, fruit, and oats have low glycemic indexes, despite their high carbohydrate content, due mostly to the health-promoting effects of soluble fiber.
Diabetes disrupts the mechanisms by which the body controls blood sugar. Until recently, health professionals have recommended sugar restriction to people with diabetes, even though short-term high-sugar diets have been shown, in some studies, not to cause blood sugar problems in people with diabetes. Currently, the American Diabetic Association (ADA) guidelines do not prohibit the use of moderate amounts of sugar, as long as blood levels of glucose, triglycerides, and cholesterol are maintained within normal levels.
Most doctors recommend that people with diabetes to reduce the amount of sugar eaten in snacks and processed foods, and replace these foods with high-fiber, whole foods. This tends to lower the glycemic index of the overall diet and has the additional benefit of increasing vitamin, mineral, and fiber intake. Other authorities also recommend lowering the glycemic index of the diet to improve the control of diabetes.
A high-fiber diet has been shown to work better in controlling diabetes than the diet recommended by the ADA, and may control blood sugar levels as well as oral diabetes drugs. In this study, the increase in dietary fiber was accomplished exclusively by eating foods naturally high in fiber—such as leafy green vegetables, granola, and fruit—to a level beyond that recommended by the ADA. No fiber supplements were given. All participants received both the ADA diet (providing 24 grams of fiber per day) and the high-fiber diet (providing 50 grams of fiber per day) for a period of six weeks. After six weeks of following each diet, tests were performed to determine blood glucose, insulin, cholesterol, triglyceride, and other values. When glucose levels were monitored over a 24-hour period, participants eating the high-fiber diet had an average glucose level that was 10% lower than participants eating the ADA diet. Insulin levels were 12% lower in the group eating the high-fiber diet compared to the group eating the ADA diet, indicating a beneficial increase in the body’s sensitivity to insulin. Moreover, people eating the high-fiber diet experienced significant reductions in total cholesterol, triglycerides, and LDL (“bad”) cholesterol compared with those eating the ADA diet. They also had slight decreases (improvements) in glycosylated hemoglobin levels, a measure of long-term blood glucose regulation.
High-fiber supplements, such as psyllium, guar gum (found in cluster beans), pectin (from fruit), oat bran, and glucomannan, have improved glucose tolerance in some studies. Positive results have also been reported with the consumption of 1 to 3 ounces of powdered fenugreek seeds per day. A review of the research revealed that the extent to which moderate amounts of fiber help people with diabetes in the long term is still unknown, and the lack of many long-term studies has led some researchers to question the importance of fiber in improving diabetes. Nonetheless, most doctors advise people with diabetes to eat a diet high in fiber. Focus should be placed on fruits, vegetables, seeds, oats, and whole-grain products.
Eating fish also may afford some protection from diabetes. Incorporating a fish meal into a weight-loss regimen was more effective than either measure alone at improving glucose and insulin metabolism and high cholesterol.
Vegetarians have been reported to have a low risk of type 2 diabetes. When people with diabetic nerve damage switch to a vegan diet (no meat, dairy, or eggs), improvements have been reported after several days. In one trial, pain completely disappeared in 17 of 21 people. Fats from meat and dairy may also contribute to heart disease, the leading killer of people with diabetes.
Vegetarians also eat less protein than do meat eaters. Reducing protein in the diet has lowered kidney damage caused by diabetes and may also improve glucose tolerance. and may also improve glucose tolerance. However, in a group of 13 obese males with high blood-insulin levels (as is often seen in diabetes), a high-protein, low-carbohydrate diet resulted in greater weight loss and control of insulin levels, compared with a high-carbohydrate diet. Switching to either a high- or low-protein diet should be discussed with a doctor.
Diets high in fat, especially saturated fat, worsen glucose tolerance and increase the risk of type 2 diabetes, an effect that is not simply the result of weight gain caused by eating high-fat foods. Saturated fat is found primarily in meat, dairy fat, and the dark meat and skins of poultry. In contrast, glucose intolerance has been improved by diets high in monounsaturated oils, which may be good for people with diabetes. The best way to incorporate monounsaturates into the diet is to use olive oil, especially extra virgin olive oil, which has high antioxidant values.
Lifestyle changes that may be helpful
Most people with type 2 diabetes are overweight. Excess abdominal weight does not stop insulin formation, but it does make the body less sensitive to insulin. Excess weight can even make healthy people prediabetic, though weight loss can reverse this problem. In most studies, type 2 diabetes has improved with weight loss.
Exercise helps decrease body fat and improve insulin sensitivity. People who exercise are less likely to develop type 2 diabetes than those who do not. However, exercise can induce low blood sugar in diabetics taking blood sugar–lowering medications, or even occasionally increased blood sugar.(Therefore, people with diabetes should never begin an intensive exercise program without consulting a healthcare professional.
Moderate alcohol drinking in healthy people improves glucose tolerance. However, alcohol has been reported to worsen glucose tolerance in the elderly and in people with diabetes in some studies. People with diabetes who drink have also been reported to have a high risk for eye and nerve damage.
Questions remain about where the line should be drawn regarding alcohol intake. For healthy people, light drinking will not increase the risk of diabetes, and may even reduce the risk of developing type 2 diabetes; however, heavy drinking does increase the risk of developing diabetes and should be avoided. People with diabetes should limit alcohol intake to two drinks per day. Total avoidance of alcohol in people with diabetes who are not suffering from alcoholism, liver disease (e.g., cirrhosis), gastritis, ulcers, and other conditions made worse by alcohol might actually be counterproductive. In one report, older people with type 2 diabetes who drank daily, but moderately, had a dramatically lower incidence of deaths from heart disease compared with nondrinkers. This outcome is not surprising since moderate alcohol intake is associated with protection from heart disease in most other reports. This finding may be of particular importance because heart disease is the leading killer of people with diabetes. In another study, nondrinkers had a higher incidence of type 2 diabetes than did moderate drinkers.
People with diabetes who smoke are at higher risk for kidney damage, heart disease, and other diabetes-linked problems. Smokers are also more likely to develop diabetes, so it’s important for diabetic smokers to quit.
Although most healthcare professionals agree on the necessity of self-monitoring of blood glucose (SMBG) by people with type 1 diabetes, disagreement exists within the medical community regarding the efficacy and necessity of SMBG by people with type 2 diabetes. A controlled clinical trial found that home glucose monitoring strips did not affect the management of type 2 diabetes. Moreover, a review of available literature concluded that the efficacy of SMBG in people with type 2 diabetes is questionable and should be tested in a rigorous high-quality trial. Advocates of SMBG, such as the ADA, have observed that SMBG by people with diabetes has revolutionized management of the disease, enabling them to achieve and maintain specific goals. These observations are well-supported in the medical literature. Detractors point out that indiscriminate use of self-monitoring is of questionable value and adds enormously to healthcare costs. The ADA acknowledges that accuracy of SMBG is instrument- and technique-dependent. Errors in technique and inadequate use of control procedures have been shown to lead to inaccurate test results. Nevertheless, it is likely that self-monitoring of blood glucose, if used properly, can have a positive effect by increasing a person’s involvement in overall diabetes care. Pharmacists and healthcare practitioners can teach people with diabetes certain skills that will enhance their ability to properly self-manage blood glucose.
Eric R. Braverman, M.D.
Dr. Braverman is a Summa Cum Laude and Phi Beta Kappa graduate of Brandeis University and NYU Medical School, did brain research at Harvard Medical School, and trained at an affiliate of Yale Medical School. He is acknowledged worldwide as an expert in brain-based diagnosis and treatment, and he lectures to and trains doctors in anti-aging medicine.