Canola Oil May Improve Glycemic Control, Reduce Cardiovascular Risk Factors

 David J.A. Jenkins Professor and Canada Research Chair in Nutrition and Metabolism, Dept. of Medicine and Nutritional Sciences, Faculty of Medicine, University of Toronto, Toronto, ON, Interview with:
David J.A. Jenkins
Professor and Canada Research Chair in Nutrition and Metabolism,
Dept. of Medicine and Nutritional Sciences, Faculty of Medicine,
University of Toronto, Toronto, ON, Canada


MedicalResearch: What are the main findings of the study?

Prof. Jenkins: The main findings were that inclusion of just over an once (31g) of canola oil in low glycemic index diets of type 2 diabetes study participants, to further reduce the glycemic load (GL), reduced HbAIC more than a high cereal fiber diet, as predicted. However the Canola oil low GL diet also reduced serum TG and LDL-C and thus Framingham risk score for cardiovascular disease. The effect was seen most clearly in those at highest CHD risk and those with features of the metabolic syndrome.

MedicalResearch: Were any of the findings unexpected?

Prof. Jenkins: The unexpected findings were the magnitude of the effect on HbAIC in those with features of the metabolic syndrome and the lack of advantage over and above that achieved by a high cereal (wheat) fiber diet in those without metabolic syndrome features. Thus the treatment difference in HbAIC for participants with a systolic BP greater than 130 was over 0.4%, considered by FDA to be a therapeutic effect (i.e. above 0.3 -0.4%). On the other hand those on the test with lower BP values at baseline showed no significant advantage over the control.

Perhaps in retrospect these data should not be unexpected since others have also noted that those with a greater likelihood of insulin resistance showed the greatest benefits of low glycemic index/glycemic load diets. Thus Ebbling and Ludwig (1) demonstrated that a treatment difference in weight loss in overweight study participants was only seen in those who had raised 30 min postprandial insulin levels as a marker of insulin resistance (1). Earlier, Liu et al. noted in the Nurses’ Health Study that only women with a BMI greater that 23Kg/m2 showed an increase in CHD risk with a higher glycemic load diet (2), another association with insulin resistance.

We conclude that those with the greater degree of insulin resistance are likely to benefit most from interventions such as reducing the dietary GI/GL that reduce post prandial glycemia.

MedicalResearch: What should clinicians and patients take away from your report?

Prof. Jenkins: Clinicians and patients may want to continue the focus on plant foods in the diet and consider including Canola oil in their diets not only for cooking purposes but more importantly as the cold oil in salad dressings, on boiled vegetables to increase palatability and on snack foods such as bruschetta in much the same situation as olive oil is used in Mediterranean cuisine. The uses of both olive (PREDIMED)(3) and Canola (Lyon Heart Study) (4) have been shown to reduce CVD in clinical trials. Canola oil may be used with advantage as part of a low glycemic load diet with focus on legumes (chick peas, beans and lentils) and other low GI foods such as parboiled rice, burglar, heavy pumpernickel bread and with the use of nuts to further lower the glycemic load.

MedicalResearch: What recommendations do you have for future research as a result of this study?

Prof. Jenkins: The future research called for by this and other similar studies is the pressing need for long term hand endpoint (MACE etc.) studies to indicate the possible advantages of these dietary interventions, and identification of the individuals most likely to benefit. An unified call for studies in this area is especially warranted when funding agencies are staying away from funding diet and lifestyle trials due to their very significant cost, a cost which nevertheless is in proportion to the public good to be derived from the subsequent evidence based diet and lifestyle advice.

In terms of the studies themselves every effort should be made to recruit vulnerable populations to derive the greatest benefit from low GI/GL diets. It is likely that studies on individuals without significant broad evidence of insulin resistance may be flawed by type 2 error, with potentially useful interventions discarded due to negative results that may have shown significant benefits if applied to individuals at higher risk.

  1. Ebbeling CB, Leidig MM, Feldman HA, Lovesky MM, Ludwig DS. Effects of a low-glycemic load vs low-fat diet in obese young adults: a randomized trial. JAMA. 2007 May 16;297(19):2092-102.
  2. Liu S, Willett WC, Stampfer MJ, Hu FB, Franz M, Sampson L, Hennekens CH, Manson JE. A prospective study of dietary glycemic load, carbohydrate intake, and risk of coronary heart disease in US women. Am J Clin Nutr. 2000 Jun;71(6):1455-61.
  3. Estruch R, Ros E, Salas-Salvadó J, Covas MI, Corella D, Arós F, Gómez-Gracia E, Ruiz-Gutiérrez V, Fiol M, Lapetra J, Lamuela-Raventos RM, Serra-Majem L, Pintó X, Basora J, Muñoz MA, Sorlí JV, Martínez JA, Martínez-González MA; PREDIMED Study Investigators. Primary prevention of cardiovascular disease with a Mediterranean diet. N Engl J Med. 2013 Apr 4;368(14):1279-90. doi: 10.1056/NEJMoa1200303. Epub 2013 Feb 25.
  4. de Lorgeril M, Renaud S, Mamelle N, Salen P, Martin JL, Monjaud I, Guidollet J, Touboul P, Delaye J. Mediterranean alpha-linolenic acid-rich diet in secondary prevention of coronary heart disease. Lancet. 1994 Jun 11;343(8911):1454-9.



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

David J.A. Jenkins, Cyril W.C. Kendall, Vladimir Vuksan, Dorothea Faulkner, Livia S.A. Augustin, Sandra Mitchell, Christopher Ireland, Korbua Srichaikul, Arash Mirrahimi, Laura Chiavaroli, Sonia Blanco Mejia, Stephanie Nishi, Sandhya Sahye-Pudaruth, Darshna Patel, Bashyam, Edward Vidgen, Russell J. de Souza, John L. Sievenpiper, Judy Coveney, Robert G. Josse, and Lawrence A. Leiter

Diabetes Care published ahead of print June 14, 2014, doi:10.2337/dc13-2990 1935-5548