Well, lookie here … turns out canola oil may help people with type 2 diabetes control their glucose levels. At least that’s the conclusion from a study reported in Science Daily with the rah-rah headline Canola oil may be an oil of choice for people with type 2 diabetes:
Canola is Canada’s oil and new research from St. Michael’s Hospital suggests it should also be one of the oils of choice for people with Type 2 diabetes. Dr. David Jenkins, head of the hospital’s Clinical Nutrition and Risk Factor Modification Centre, compared people with Type 2 diabetes who ate either a low glycemic index diet that included bread made with canola oil, or a whole wheat diet known to reduce the risk of cardiovascular disease.
His study, published today in the journal Diabetes Care, found that those on the canola bread diet experienced both a reduction in blood glucose levels and a significant reduction in LDL, or “bad,” cholesterol.
Even more exciting, he said, was the finding that the canola bread diet seemed to have the most significant impact on people who needed help the most — those whose HbA1c test measuring blood glucose over the previous two or three months was highest.
Well, that’s it, then. Time to call all your friends and relatives with type 2 diabetes and tell them to stock up on canola oil so they can go on that canola bread diet. Clearly some specific property in an oil chemically extracted from rapeseeds helps control diabetes.
On the other hand, maybe we should take a peek at the study first. Here’s part of the abstract:
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.
Hmmm … economics professor Thomas Sowell (author of The Vision of the Anointed) once wrote that when students in his classes declared this-or-that to be good or bad, he always replied with “Compared to what?” Seems to me this study didn’t compare canola oil to any other fats or oils; it compared two rather different diets, one of which happened to include canola oil. So I found the full study. Here are some quotes from that:
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.
The study followed a randomized, parallel design with two treatment arms of 3 months duration as follows: 1) a low-GL diet with a canola oil–enriched bread provided as a supplement (test) or 2) a high wheat-fiber diet emphasizing whole-wheat foods (control).
The dietitians and participants could not be blinded …
I understanding blinding a group of dieticians wouldn’t get past the ethics committee, but couldn’t we at least poke them in the eye?
… but equal emphasis was placed on the potential importance of both diets for health.
Okay, so no placebo effect. Both groups were told they were going on a good diet.
The test diet included 4.5 slices of canola oil–enriched whole-wheat bread (500 kcal/day) provided as a supplement. The supplement delivered 31 g canola oil or 14% of total dietary calories of a 2,000-kcal diet. The control diet included 7.5 slices of whole-wheat bread without canola oil per day (500 kcal).
A little math tells us the canola oil provided 280 of the 500 calories in the bread. In other words, the canola bread was 56% fat by calories, or 62 fat calories per slice. We can also determine that the canola bread contained 111 total calories per slice. The wheat breads I looked up online also contain 3-4 grams of protein per slice, so let’s figure 3.5 * 4 cals/gram = 14 protein calories … now subtract here, divide there, roll a set of dice, count on our fingers … I’m getting a figure of 8.78 carbs per slice on the canola bread. Multiplied by 4.5 slices per day, that’s 39.5 carbs from the canola bread.
The commercial whole-wheat breads I looked up contain around 12 carbs per slice. Multiplied by 7.5 slices per day, that’s 90 carbohydrates. So that’s a good guess as to what the control group was consuming as carbohydrates from bread. Now if only we had an idea about the non-bread portions of the two diets …
Dietary advice on the test diet emphasized low-GI foods, including legumes, barley, pasta, parboiled rice, and temperate-climate fruit, as outlined in previous studies. For the control diet, participants were instructed to avoid white-flour products and replace them with whole-wheat breakfast cereals, study breads, brown rice, and so forth.
Boy, if I didn’t know better, I’d say the canola-bread diet was designed to result in both a higher fat intake and a lower carbohydrate intake, and hence a lower glycemic index than the control diet.
By design, the test diet resulted in significantly greater increases in MUFA and ALA intake and corresponding lower carbohydrate intake, and hence GL, relative to the control diet.
I see. So what this study actually demonstrated is that replacing calories from refined carbohydrates with calories from fat results in better glucose control. And yet the headline in Science Daily was about the wonders of canola oil, and the study’s conclusion was:
A canola oil–enriched low-GL diet improved glycemic control in type 2 diabetes, particularly in participants with raised SBP …
I’m thinking the canola oil itself had nothing to do with it. The answer to Sowell’s question (“Compared to what?”) is that compared to a diet that includes bread and cereal, a fattier diet with a lower glycemic index is better for diabetics. Perhaps canola oil got such a special mention because of this fact, which appeared at the bottom of the Science Daily article:
This research was funded by the Canola Council of Canada, Agriculture and Agri-Food Canada, Loblaw Companies, and the Canada Research Chairs Program.
For the record, I don’t know if canola oil has any harmful effects on humans. There are internet articles claiming canola oil will cause a slew of health horrors, but I don’t find those articles convincing. Perhaps canola oil has a neutral effect on health. But I don’t consume the stuff for two reasons:
One, the whole pitch for canola oil is that it’s mostly monounsaturated, like olive oil – i.e., it’s very low in artercloggingsaturatedfat! Well, heck, even TIME magazine has come around to admitting that there’s no need to avoid saturated fat. (Check out this TIME video on that subject.) So at best, canola oil is an answer in search of a problem.
Two, this is how it’s made:
I’d rather not consume a fat that has to be bleached and de-odorized before it reaches a state we could charitably call “not disgusting.” Coconut oil, butter, bacon grease, beef tallow, chicken fat – they all taste great without any industrial processing. And if you replace the refined carbohydrates in your diet with any one of them, you’ll probably end up with better glucose control.
