Effect of Nuts vs. a Wheat Bran Muffin in Type 2 Diabetes

To determine if tree nuts (Almonds, Hazelnuts, Pistachios, Peanuts, Macadamia nuts, Pecans, Walnuts and Cashews) improve glycemic control in type 2 diabetes, as assessed by HbA1c and serum fructosamine, and to assess whether these outcomes relate to improvements in cardiovascular health (i.e. plasma lipids and measures of oxidative stress, inflammatory biomarkers and nitric oxide generation). The investigators have found that nuts tend to reduce the glycemic index of bread and have little effect of raising blood glucose on their own. Therefore the investigators believe that they would be ideal foods to displace high glycemic foods from the diet and lower the dietary glycemic load. This will result in improved blood glucose control in type 2 diabetes, with additional benefits on coronary heart disease risk factors due to other effects of nuts.

The investigators wish to study the effect of nuts on glycemic control and to confirm their lipid lowering effects in type 2 diabetes. The consumption of nuts with their high unsaturated fat, vegetable protein (arginine) and fiber contents will decrease the glycemic load of the diet and improve glycemic control. The investigators anticipate that the favorable fatty acid profile of nuts along with the vegetable protein will improve the blood lipid profile in type 2 diabetes and thereby establish a cardiovascular risk reduction associated with nuts in this population.

Furthermore, flavonoids and vitamin E present in high concentrations in nuts, and known to have antioxidant activity may help to counter the elevated oxidative stress and inflammation experienced by diabetics. The investigators will therefore determine the effect of nut feeding on measures of oxidative stress (including oxidized low-density lipoprotein cholesterol (LDL-C), considered to be of direct relevance to coronary heart disease), inflammation (C-reactive protein, serum amyloid A and interleukin-6) and nitric oxide metabolism (blood nitric oxide and nitrotyrosine levels). These data would further add to interest in nuts in relation to cardiovascular disease risk reduction and diabetic complications.

Background Diet: A diet conforming to the American Diabetes Association (ADA) and National Cholesterol Education Program (NCEP) Adult Treatment Panel III guidelines. Nuts, soy and dietary supplements (vitamins, minerals, herbal remedies) will be excluded in the background diet during all phases of the study.

Treatment diets:(1) Full-Dose Nut Diet: Raw nuts will be added as supplements to the subject's usual diet. Subjects with calorie needs of 2,400 kcal or greater, assessed by Lipid Research Clinic (LRC) tables, will receive the full-dose supplement (100 g/d of nuts, approximately 600 kcal). Subjects requiring between 1,600-2,400 kcal daily will receive 75% of the full-dose supplement (75 g/d of nuts, approximately 450 kcal). Subjects requiring less than 1,600 kcal daily will receive 50% of the full-dose supplement (50 g/d of nuts, approximately 300 kcal). (2) Half-Dose Nut Diet: Raw nuts will be added as supplements to the subject's usual diet. Subjects with calorie needs of 2,400 kcal or greater, assessed by LRC tables, will receive half of the full dose of the nut supplement (50 g/d of nuts, approximately 300 kcal) with the rest of the calories provided by the muffin (2 muffins are 300 kcal) for a total of 600 kcal. Subjects requiring between 1,600-2,400 kcal daily will receive 75% of the half-dose supplement (37.5 g/d of nuts and 1.5 muffins, approximately 450 kcal). Subjects requiring less than 1,600 kcal daily will receive 50% of the half-dose supplement (25 g/d of nuts and 1 muffin, approximately 300 kcal). (3): The full-dose control supplement will be four 150 kcal muffins. Control supplements will be matched with the energy content of the nut supplements, i.e. either 600 kcal/d (4 muffins); 450 kcal/d (3 muffins); 300 kcal/d (2 muffins). The macronutrient composition of the muffins will conform to an NCEP Step 2 diet with 25% total fat, <7% saturated fat by use of corn oil as the oil commonly used in healthy baked goods, with 18% protein (the average for our subject population) using added skim milk powder, and zero cholesterol. Muffins will be made with whole wheat flour.

Diet History: one-week weighed diet histories will be obtained prior to the start and at weeks 4, 8 and 12 of the study for assessment of macronutrients, dietary fiber and fatty acids.

Palatability/Satiety: for palatability and satiety, subjects will record their ratings using a 7-point bipolar semantic scale at monthly intervals during each study phase.

Anthropometry and Blood Pressure: height at recruitment and body weight, blood pressure, waist and hip circumference, and body composition will be taken immediately prior to and at each clinic visit (wk 0, 2, 4, 8, 10, 12) during the study.