Effect of Lowering the Glycemic Load With Canola Oil on Glycemic Control and Cardiovascular Risk Factors: A Randomized Controlled Trial

  1. Lawrence A. Leiter1,2,3,4,5
  1. 1Department of Nutritional Sciences, Faculty of Medicine, University of Toronto, Toronto, ON, Canada
  2. 2Department of Medicine, Faculty of Medicine, University of Toronto, Toronto, ON, Canada
  3. 3Clinical Nutrition and Risk Factor Modification Center, St. Michael’s Hospital, Toronto, ON, Canada
  4. 4Division of Endocrinology and Metabolism, St. Michael’s Hospital, Toronto, ON, Canada
  5. 5Li Ka Shing Knowledge Institute of St. Michael's Hospital, Toronto, ON, Canada
  6. 6College of Pharmacy and Nutrition, University of Saskatchewan, Saskatoon, SK, Canada
  7. 7Medical School, Faculty of Medicine, University of Ottawa, Ottawa, ON, Canada
  8. 8School of Medicine, Faculty of Health Sciences, Queen's University, Kingston, ON, Canada
  9. 9Department of Clinical Epidemiology and Biostatistics, Faculty of Health Sciences, McMaster University, Hamilton, ON, Canada
  10. 10Department of Pathology and Molecular Medicine, Faculty of Health Sciences, McMaster University, Hamilton, ON, Canada
  1. Corresponding author: David J.A. Jenkins, nutritionproject{at}smh.ca.

Abstract

OBJECTIVE Despite their independent cardiovascular disease (CVD) advantages, effects of α-linolenic acid (ALA), monounsaturated fatty acid (MUFA), and low-glycemic-load (GL) diets have not been assessed in combination. We therefore determined the combined effect of ALA, MUFA, and low GL on glycemic control and CVD risk factors in type 2 diabetes.

RESEARCH DESIGN AND METHODS The study was a parallel design, randomized trial wherein each 3-month treatment was conducted in a Canadian academic center between March 2011 and September 2012 and involved 141 participants with type 2 diabetes (HbA1c 6.5%–8.5% [48–69 mmol/mol]) treated with oral antihyperglycemic agents. Participants were provided with dietary advice on either a low-GL diet with ALA and MUFA given as a canola oil–enriched bread supplement (31 g canola oil per 2,000 kcal) (test) or a whole-grain diet with a whole-wheat bread supplement (control). The primary outcome was HbA1c change. Secondary outcomes included calculated Framingham CVD risk score and reactive hyperemia index (RHI) ratio.

RESULTS Seventy-nine percent of the test group and 90% of the control group completed the trial. The test diet reduction in HbA1c units of −0.47% (−5.15 mmol/mol) (95% CI −0.54% to −0.40% [−5.92 to −4.38 mmol/mol]) was greater than that for the control diet (−0.31% [−3.44 mmol/mol] [95% CI −0.38% to −0.25% (−4.17 to −2.71 mmol/mol)], P = 0.002), with the greatest benefit observed in those with higher systolic blood pressure (SBP). Greater reductions were seen in CVD risk score for the test diet, whereas the RHI ratio increased for the control diet.

CONCLUSIONS A canola oil–enriched low-GL diet improved glycemic control in type 2 diabetes, particularly in participants with raised SBP, whereas whole grains improved vascular reactivity.

  • Received December 20, 2013.
  • Accepted April 15, 2014.

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