• Note that one of the studies was published as an abstract and presented at a conference. Those data and conclusions should be considered to be preliminary until published in a peer-reviewed journal.
• Improving overall diet quality over a 4-year period, independent of increased physical activity and body weight loss, was associated with reduced risk of diabetes in healthy adults.

SAN FRANCISCO — 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, 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 148,479 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.

Clinical Implications

“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,” commentedMelinda 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 MedPage Today 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 MedPage Today.

“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.