Dietary modifications can be a powerful tool for preventing and treating diabetes. If, for example, a clinician is treating a patient who is at a high risk of developing type 2 diabetes before symptoms of hyperinsulinemia and=or hyperglycemia become acute, this is an excellent opportunity to emphasize the potential benefit of cereal fiber. In a large prospective study of 65,173 females over six years, researchers looked for associations between the glycemic index of subjects' diets and their risk of developing type 2 diabetes.60 A glycemic index is an indication of a food's potential to raise blood glucose and the demand the food creates for insulin. Foods with a high glycemic index generally include items such as white bread, mashed potatoes, white rice, and cola beverages. More intermediate-range glycemic foods are items such as apples and orangejuice. Low-glycemic foods are generally those that maintain their natural unprocessed fibers, such as broccoli and peanut butter. In this prospective study, women in the quintile with the highest average glycemic index had a significantly higher risk of developing type 2 diabetes compared to women with the lowest average glycemic index. One of the strongest associations for an individual food type was seen in the analysis of cereal fiber intakes and the risk for developing diabetes. Women in the study quintile with the highest median cereal fiber intake (7.5 g per day) had an RR of 0.72 of developing type 2 diabetes compared to the women in the quintile with the lowest median intake of cereal fiber (2.0 g per day). In contrast, women with a diet characterized by a high glycemic load and a low cereal fiber intake had an RR of 2.50 for developing type 2 diabetes compared to women eating a diet with a low glycemic load and high cereal fiber. Results from the same research team following a sample of more than 42,000 men prospectively were similar.61
An additional association in this work that was significant was the risk of diabetes and magnesium intake. In the women's study, subjects with a median intake of 338 mg per day had an RR of 0.62 compared to women with a median intake of 222 mg per day. This is especially important to keep in mind because a lack of sufficient magnesium is so easily remedied by magnesium supplementation. In fact, although supplementation did not seem to improve glycemic control in subjects who were already diagnosed with type 2 diabetes, there is research showing that magnesium levels tend to be low in subjects with diabetes and that three months of supplementation is adequate for reversing the problem.62
One form of fiber that may be particularly useful for treating patients once they are diagnosed with either type 1or type 2 diabetes is the fiber from legumes. In one study of 9 patients with type 1 diabetes and 18 with type 2 diabetes, subjects were placed for six weeks on a high carbohydrate diet that was rich in legumes and then also a low-carbohydrate diet for six weeks.63 In subjects with diabetes of either type, the mean preprandial and two-hour postprandial blood glucose levels were significantly lower when the subjects were on the diet that was rich in legumes. The amount of glucose passed in the subjects' urine was also significantly less when they were on the high legume diet.
An additional consideration in the diet of patients with diabetes is the amount of protein they consume in relation to the health of their kidneys. One commonly referred to hypothesis suggests that too much protein intake causes hyperfiltration and glomerular hypertension, which leads to reduced kidney function and eventual nephropathy in some patients with diabetes.64 Clinical data that seem to support this hypothesis come from trials that have utilized limited protein intake and have shown subsequent, significant drops in glomerular filtration rate (GFR) and=or the amount of albumin excretion in subjects with diabetes.65,66 The complete relationship between protein consumption and kidney health in patients who have diabetes is a complex one and is beyond the scope of this book. One interesting hypothesis, however, is that, while some forms of protein, especially beef, increase postprandial renal plasma flow and GFR, soy does not seem to alter postprandial renal function, suggesting that substituting soy for animal protein might protect patients who have diabetes from nephropathy.67 Unfortunately, a small pilot study designed to test this hypothesis, in which eight men with type 2 diabetes replaced half of their protein intake with soy protein, failed to show reduction in proteinuria. However, the study is important because it helps us to consider the concept that effects of protein intake on kidney health in patients with diabetes may be dependent on the type of protein being consumed. While we are still a long way from understanding the perfect diet for patients with diabetes, understanding which types of proteins will spare kidney function most effectively, and thus delay the onset of nephropathy, could certainly be a fruitful field for future research.
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