There was a time when buying bread was a simple choice between a loaf of white, brown or occasionally rye. Today, the bread aisle at the grocery store offers options from whole wheat to stone ground whole grain flax bread with omega 3.
But Terry Graham, professor in the nutritional sciences department at Ontario’s University of Guelph, has determined that the choices are not that confusing because white bread and whole wheat bread have the same health benefits for consumers.
Graham made this discovery as part of an ongoing study where he’s trying to find out how different breads affect carbohydrate metabolism and blood sugar levels in the body.
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“(We took) a group of unfortunately typical Canadians, in that they are middle aged, sedentary, overweight … and we had them consume different types of breads (for breakfast),” he said, noting that they used four different types of bread in the study – whole wheat, white, sourdough and whole wheat with added barley.
Graham and his colleagues then monitored the subject’s response to the bread for three hours to measure how quickly the body metabolized the starch into sugar.
Researchers thought the whole wheat and the whole wheat with barley breads would be the “shining stars,” Graham said.
But the results, which have been published in the British Journal of Nutrition, did not meet that expectation.
“The response to the whole-wheat breads was no different, it certainly was no more optimal … than the response to white bread,” he said, noting that both breads caused blood sugar levels to rise at similar rates.
Graham later concluded that the response was the same because whole wheat bread is only marginally different from white bread.
“If you go down the grocery store aisle, you’ll see all these whole wheat breads … (But) if you actually sample them, they have the mouth-feel and the taste that’s pretty much like white bread,” he said.
“Ninety percent of all the breads consumed in North America are either white or whole wheat.”
Graham explained that North American consumers prefer bread with a “soft, mushy” texture, which forces millers to make whole wheat breads from fine grained flour.
“The parts of the grain like wheat germ and bran that have the health benefits are taken out to create white flour and then partially added back in to make whole wheat (flour).”
The other surprise from Graham’s study was that sourdough bread came out on top, because it was the best at regulating blood sugar levels, an essential trait for diabetics and a health benefit for most consumers.
“You want to see the smallest rise in blood sugars…. With the sourdough bread, we saw the best responses in blood sugar.”
Steve Ciu, an Agriculture Canada research scientist who worked with Graham on the study, explained that sourdough provides a different form of carbohydrate than other breads.
The fermentation process to make sourdough produces oligosaccharides, a carbohydrate found in legumes, onions and asparagus, which has three to 10 simple sugar molecules linked in a chain.
“This material (oligosaccharides) cannot be digested by our enzymes … they will stay in the body and cannot be digested (in the stomach or small intestine),” said Ciu.
Instead the carbohydrate slips into the large intestine where it ferments to produce beneficial fatty acids.
Because this type of carbohydrate is digested much more slowly, blood sugar levels do not spike immediately after eating sourdough bread.
Following this study, Graham began looking at subjects’ blood sugars after they ate whole grain bread for breakfast.
“(Whole wheat) is very different from whole grain,” he said. “(With whole grain) you’re going to have more of the important nutrients beyond starch. You’re going to have all of the bran and all of the wheat germ. So you’re getting fibre and a number of vitamins.”
Although the study is not yet published, Graham said it showed that whole grain breads are indeed better at controlling blood sugar than whole wheat, but the results varied from bread to bread.
“I’d love to be able to tell your readers that all the whole grain breads are really good. But you could see different responses depending on which of the products (was consumed),” he said.
Asked what type of bread he eats, Graham said he prefers sourdough whole grain breads.
