Adding canola oil to the diet improved glycemic control and reduced cardiovascular risk in type 2 diabetes in one study, while an overall healthier diet reduced risk of developing diabetes in another.
An extra ounce of the vegetable oil daily, incorporated into bread, cut hemoglobin A1c by 0.47% compared with a 0.31% decline on a control diet emphasizing whole grains (P=0.002), David J.A. Jenkins, MD, PhD, ScD, of the University of Toronto, and colleagues found in a randomized trial.
Framingham risk score for cardiovascular disease dropped across the 12-week trial in both groups, but by 0.6 percentage points more from the baseline 10% risk with the canola diet than with the control (P=0.008), they reported here at the American Diabetes Association meeting and simultaneously online in Diabetes Care.
In a second trial reported at the meeting, improving diet quality score by 10 points on a 110-point summary scale — assessing fruit, vegetable, nuts, polyunsaturated fat, and other factors — over 4 years was associated with a 9% lower risk of diabetes incidence over the next 4 years (95% CI 0.84-0.99).
The same degree of decrease in diet quality was associated with an 18% increase in risk (95% CI 1.08-1.30), independent of changes in weight, physical activity, and caloric intake and other factors, Sylvia Ley, PhD, RD, of the Harvard School of Public Health in Boston, and colleagues found in a pooled trial analysis.
That study included the Nurses’ Health Study I and II and the Health Professionals Follow-up Study, for a total of 2148,479 participants without baseline diabetes, cardiovascular disease, or cancer.
Notably, the relationship with diabetes incidence held across groups with baseline high, low, and intermediate diet quality assessed by the Alternative Healthy Eating Index score.
“Here is evidence that spending a little bit of time with your patient to make sure that they work toward clarity on what healthy food choices are does make a difference,” commented Melinda Maryniuk, RD, director of clinical education programs at Joslin Diabetes Center in Boston.
The diet quality findings weren’t any surprise, “but isn’t it great to have more science to prove what we think makes a lot of sense?” she told reporters at a press conference she chaired.
Just saying “lose weight” might not be as useful and isn’t as easy for patients to accept, she noted.
Telling patients “eat more fruits and vegetables” isn’t that useful either, Jenkins added.
“It has become a sort of superficial giveaway thing that somebody says in a doctor’s office,” he told Reporters.
“The patient goes away and may not increase to five to 10 servings a day because they don’t really know how to do it, they’re not really interested in doing it, and they don’t see the evidence.”
Olive oil has the evidence to put it in the “healthy” category, from trials such as PREDIMED, which found a 30% cardiovascular risk reduction and 40% diabetes risk reduction with extra olive oil in a Mediterranean diet compared with a low-fat diet.
“Canola oil and other oils can also be put into this particular envelope of nutrients — foods that, I think, displace foods which are not so healthy, the saturated fat foods, the animal products, and the highly refined carbohydrates,” Jenkins said.
Also, “it could be a cheaper option,” he noted.
The Canola Diet
Canola oil was used as a source of a-linolenic acid, an omega-3 fatty acid, and other monounsaturated fatty acids, which have previously been shown to delay gastric emptying and thus slow the release of carbohydrates.
In the trial, canola oil cut the glycemic index of the diet by 19 points compared with the whole-grain diet.
The trial included 141 people on oral medications for type 2 diabetes randomized to dietary advice on either a low-glycemic index diet with 4.5 slices of a canola oil-enriched bread daily or a whole-grain diet with 7.5 slices of whole-wheat bread.
“Such whole-grain diets have invariably been associated with a reduced risk of diabetes and cardiovascular disease in cohort studies, despite generally having no effect on conventional cardiovascular disease risk factors,” Jenkins’ group noted.
While weight change was similar across groups, LDL and triglycerides declined significantly more in the canola group.
The benefit accrued significantly only in higher metabolic-risk groups.
Participants with systolic blood pressure over 130 mm Hg got more than five times the treatment effect on HbA1c from the canola intervention than did participants with a lower blood pressure (-0.41% versus -0.07%, P=0.003).
The absolute impact of canola was 0.62% over baseline in the high blood pressure group and well in the range of what the FDA looks for in diabetes drug development, the researchers noted.
Findings were similar when analyzing by baseline waist-to-height ratio and baseline cardiovascular disease risk.
Disclosure: The study by Jenkins’ group was supported by the Canola Council of Canada, Agriculture and Agri-Food Canada, and Loblaw Companies.
Jenkins disclosed relationships with the federal government of Canada, the Canadian Institutes of Health Research, Canada Foundation for Innovation, Ontario Research Fund, Canola Council of Canada, the International Tree Nut Council Nutrition Research & Education Foundation, Alpro Foundation, Peanut Institute, Unilever, Sanitarium Company, 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, Saskatchewan Pulse Growers, the Almond Board of California, Barilla, Solae, Oldways, Kellogg’s, Loblaw Brands, Barilla, Haine Celestial, Sanitarium Company, and Orafti; Canola Council of Canada, and the Nutrition Foundation of Italy.
Disclosure: Jenkins reported that his wife is part owner of Glycemic Index Laboratories, a contract research organization. Ley dislcosed no conflicts of interest.
Reference: Jenkins DJA, et al “Effect of lowering the glycemic load with canola oil on glycemic control and cardiovascular risk factors: A randomized controlled trial” Diabetes Care 2014; DOI: 10.2337/dc13-2990.
Additional source: American Diabetes Association
Source reference: Ley SH, et al “Changes in overall diet quality, lifestyle, and subsequent risk of type 2 diabetes: Three cohorts of U.S. Men and women” ADA 2014; Abstract 74-OR.