July 13, 2011 — Mixed nuts may be a good replacement for some carbohydrates in the diabetic diet, according to the results of a randomized controlled trial reported online June 29 in Diabetes Care.
"Fat intake, especially monounsaturated fatty acid (MUFA), has been liberalized in diabetic diets to preserve HDL [high-density lipoprotein] cholesterol and improve glycemic control, yet the exact sources have not been clearly defined," write David J. A. Jenkins, MD, from the Clinical Nutrition and Risk Factor Modification Center at St. Michael's Hospital Toronto in Ontario, Canada, and colleagues. "Therefore, we assessed the effect of mixed nut consumption as a source of vegetable fat on serum lipids and HbA1c [hemoglobin A1c] in type 2 diabetes."
For 3 months, 117 participants with type 2 diabetes were randomly assigned to receive 1 of 3 treatments, with supplements given at 475 kcal per a 2000-kcal diet as mixed nuts (75 g/day of unsalted and mostly raw almonds, pistachios, walnuts, pecans, hazelnuts, peanuts, cashews, and macadamias), muffins with similar protein content to the nuts but no MUFAs, or half portions of both. Change in HbA1c level was the main study endpoint.
Compared with muffins, the full-nut dose was associated with a relative increase in MUFAs of 8.7% energy. The full-nut dose (mean intake, 73 g/day) was associated with a decrease in HbA1c levels of −0.21% absolute HbA1c units (95% confidence interval [CI] −0.30 to −0.11; P < .001), but there was no change with the half-nut dose or muffin, according to the intent-to-treat analysis (n = 117). The half-nut dose was not significantly different from muffin, but the full-nut dose was significantly different from both the half-nut dose (P = .004) and muffin (P = .001).
Compared with muffins, the full-nut dose was associated with a significant reduction in levels of low-density lipoprotein (LDL) cholesterol. With the half-nut dose, there was an intermediate reduction in LDL cholesterol levels, but this finding did not differ significantly from the other treatments. Similar patterns were observed with improvements in the apolipoprotein (apo) B and the apoB:apoA1 ratio. There was an inverse association of nut intake with changes in levels of HbA1c (r = −0.20; P = .033) and LDL cholesterol (r = −0.24; P = .011).
"Two ounces of nuts daily as a replacement for carbohydrate foods improved both glycemic control and serum lipids in type 2 diabetes," the study authors write.
Limitations of this study include use of a self-reported 7-day diet history, lack of blinding for participants and dietitians, high nut consumption, and the attempt to show a dose response to nuts when the primary objective of establishing whether nuts improved glycemic control had not first been demonstrated.
"[N]ut consumption not only improved glycemic control but also lipid risk factors for [coronary heart disease]," the study authors conclude. "We have no explanation for the lack of antioxidant effects of nuts seen with previous studies but may relate to antioxidants in wheat bran and apple concentrate used in the muffins. We conclude that mixed, unsalted, raw, or dry-roasted nuts have benefits for both blood glucose control and blood lipids and may be used to increase vegetable oil and protein intake in the diets of type 2 diabetic patients as part of a strategy to improve diabetes control without weight gain."
The Canada Research Chair Endowment of the Federal Government of Canada, the International Tree Nut Council Nutrition Research & Education Foundation, and the Peanut Institute supported this study. Two of the study authors have disclosed various financial relationships with Unilever, the Sanitarium Company, the California Strawberry Commission, the Almond Board of California, the International Tree Nut Council Nutrition Research & Education Foundation, Barilla, Unilever Canada, and/or Loblaws.
