Canola Oil, Low-GI Diet May Help Heart Health in Diabetes

Marlene Busko

June 26, 2014

Patients with type 2 diabetes who ate a low–glycemic-index (GI) diet enriched with canola oil had better glycemic control and cardiovascular disease risk scores, compared with those on whole-grain control diets, in a new 3-month study.

And improvements were greatest in patients with the worst metabolic profiles, David J. A. Jenkins, MD, from the University of Toronto, Ontario, reported at the American Diabetes Association (ADA) 2014 Scientific Sessions. The research was simultaneously published online in Diabetes Care.

HbA1c levels dropped by 0.47% in patients who ate the test diet compared with 0.31% in those on the control diet. And Framingham risk scores improved by about 6% more in patients who followed the test diet, largely driven by a drop in LDL-cholesterol levels.

Notably, "people who appeared to be at highest risk, who had more insulin resistance and high blood pressure and were fatter around the waist, were the people who benefited most" from the canola-oil/low-GI diet, Dr. Jenkins told Medscape Medical News.

This research provides support for eating "a lower–glycemic-load diet, [where] one takes a little bit more nonhydrogenated vegetable oil in place of some carbohydrate foods," he said. Patients did well on both diets, however, which was perhaps not surprising, since a whole-grain diet "has excellent cardiovascular benefits and was not just a 'straw-man' control."

Healthy Vegetable Oil plus Low-GI Carbohydrates

Monounsaturated fatty acids and omega-3 fatty acids (such as alpha-linolenic acid) reduce CVD risk, and a diet where some carbohydrates are replaced with vegetable oil should reduce postprandial glycemia by delaying gastric emptying, the researchers explain.

The PREDIMED study has shown that a Mediterranean diet supplemented with olive oil or nuts leads to a 30% reduction in cardiovascular outcomes, Dr. Jenkins noted.

In the current study, the researchers aimed to investigate the effects of eating a low-GI diet plus canola oil, a vegetable oil containing 9.1% alpha-linolenic acid, 63% monounsaturated fatty acids, and 7% saturated fat (half that from olive oil).

They randomized 141 people with type 2 diabetes who were taking a stable dose of oral antihyperglycemic agents to the 2 diets, which each contained the same amount of calories from bread.

The 70 patients on the test diet were instructed to eat low-GI foods, including legumes, barley, pasta, rice, and temperate-climate fruits (such as apples, but not pineapple) plus 4.5 slices of canola-oil–enriched whole-wheat study bread a day (about an ounce of canola oil a day).

The 71 patients on the control diet were advised to replace white-flour products with whole-grain foods and eat 7.5 slices of whole-wheat study bread without canola oil each day.

The patients had an average age of 59, and 45% were women. At baseline, they had a mean HbA1c level of 7.3% and a mean body mass index (BMI) of 31.

In the test-diet group, 79% of participants completed the study, and 89% were compliant with the bread consumption. In the control-diet group, 90% of participants completed the study, and 77% were compliant with the bread consumption.

On average, patients on the test diet lost 2.1 kg and those on the control diet lost 1.6 kg at 3 months. LDL-cholesterol and triglyceride levels declined significantly more in patients eating the canola-oil/low-GI diet.

HbA1c levels declined most in patients who had higher baseline measures of components of metabolic syndrome and a higher Framingham risk score.

Notably, the improvement in HbA1c from the canola-oil/low-GI diet was more than 5 times greater in patients who had a baseline systolic blood pressure above 130 mm Hg compared with those with a lower blood pressure (-0.41% vs -0.07%).

In the patients with elevated baseline systolic blood pressure, the effect of the test diet on HbA1c was in the range set by the US Food and Drug Administration for diabetes drug development.

Clinical Implications

"Both strategies could potentially improve health for people with diabetes; unfortunately, our diet is so bad, either one of them could be an improvement," Judith Wylie-Rosett, EdD, RD, professor and division head for health promotion and nutrition research at Albert Einstein College of Medicine, in New York, and an associate editor of Diabetes Care, commented to Medscape Medical News.

"Systolic blood pressure tends to go up with age, and sometimes older people respond quite differently," which might explain the larger improvement in HbA1c in people with high systolic blood pressure, she noted.

The American Diabetes Association guidelines recommend a variety of dietary strategies to improve metabolic control, and it is important to bring the patient into the discussion, Dr. Wylie-Rosett added. Instead of telling patients what to eat, "ask them what they're eating and what they think they can do in terms of either increasing fiber or increasing monounsaturated fatty acids with canola oil or olive oil."

The study findings could be applied to the "5 As" steps model of intervention (ask, advise, assess, assist, and arrange). "For example, [you might advise] a patient with elevated systolic blood pressure…that they would benefit more from this diet than someone else would," she said.

This work was supported by the Canola Council of Canada, Agriculture and Agri-Food Canada, and Loblaw Companies, Canada. Dr. Jenkins has received salary support as a Canada Research Chair from the federal government of Canada and has received funding from the Canadian Institutes of Health Research, Canada Foundation for Innovation, Ontario Research Fund, Canola Council of Canada, International Tree Nut Council Nutrition Research & Education Foundation, Alpro Foundation, and Peanut Institute. He has served on the scientific advisory board of Unilever, Sanitarium, California Strawberry Commission, Loblaw Supermarket, Herbal Life International, Nutritional Fundamentals for Health, Pacific Health Laboratories, Metagenics, Bayer Consumer Care, Orafti, Dean Foods, Kellogg's, Quaker Oats, Procter & Gamble, Coca-Cola, NuVal Griffin Hospital, Abbott, Pulse Canada, and Saskatchewan Pulse Growers. He has received honoraria for scientific advice from the Almond Board of California, Barilla, Unilever Canada, Solae, Oldways, Kellogg's, Quaker Oats, Procter & Gamble, Coca-Cola, NuVal Griffin Hospital, Abbott, Dean Foods, California Strawberry Commission, and Haine Celestial. He has been on the speakers' panel for the Almond Board of California and has received research grants from Loblaw Brands, Unilever, Barilla, Almond Board of California, Solae, Haine Celestial, Sanitarium, and Orafti. He has received travel support to meetings from the Almond Board of California, Unilever, Canola Council of Canada, Barilla, Oldways, and the Nutrition Foundation of Italy. Dr. Jenkins's wife is part owner of Glycemic Index Laboratories, a contract research organization.

Diabetes Care 2014;37:1806-1814. Article

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