The type of toasted bread we eat for breakfast can affect how the body responds to lunch, a researcher at the University of Guelph has discovered.
Prof. Terry Graham, a scientist who specializes in carbohydrates, has been looking into the health benefits of various types of bread.
"One of the surprising things in our work is that whole-wheat products turned out to have the least healthy responses of all, and this is not what we expected," he said in an interview.
Using white, whole wheat, whole wheat with barley and sourdough white breads, Graham and his team of researchers examined how subjects responded after eating the bread for breakfast and again just hours after eating a standard lunch.
The 10 male subjects, who were overweight and ranged between 50 and 60 years old, showed the most positive body responses after eating sourdough white bread. Those positive responses remained even after eating a second meal that didn't include bread.
"With the sourdough, the subjects' blood sugar levels were lower for a similar rise in blood insulin," says Graham, whose findings are being published in the British Journal of Nutrition.
"What was even more interesting was that this positive effect remained during their second meal and lasted hours after."
He says that it's likely that the fermentation of the sourdough changes the nature of the starches in the bread, creating a more beneficial bread.
And while sourdough came out on top, the whole-wheat varieties used in the study came out on the bottom, even below white bread.
The whole-wheat bread caused blood sugar levels to spike and these high levels lasted until well after lunch.
Graham said the less positive blood responses sparked by the whole wheat are likely due to the fact that the milling process involved in making the whole-wheat bread used in the study is similar to that used for white bread.
"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 to make whole wheat," he says.
"Based on the findings of this study, as well as a followup study using whole grains rather than whole wheat, we are learning that the best way to get these nutrients is through whole grain, not whole wheat."
Graham says that he and his team assumed that standard white bread would be less beneficial "and everything would be better than that."
"In fact, the whole wheat and the wheat plus barley turned out to be the least healthy."
Graham cites recent literature mainly from Scandinavia suggesting that either the sourdough leavening or even taking organic acids and adding them to the dough itself could have some positive benefits in terms of metabolic response.
"And so that was our logic for incorporating a sourdough design and to facilitate a comparison would be to use an identical bread recipe but use sourdough starter instead of the standard yeast," he says.
Sourdough bread is raised with a leaven of flour and water in which wild yeasts have been encouraged to grow by keeping it warm and allowing it to ferment over a period of days. During this time, it sours and develops a characteristic tangy flavour.
Graham says the research is ongoing to find out what it is about sourdough that does this.
"And secondly if sourdough is good, what about other types of bread such as whole grain?"
Linda Haynes, former owner and now a consultant at ACE Bakery in Toronto, says she is amazed at Graham's findings and says "it is exciting that sourdough could prove to be a health benefit."
