Sweet findings for sourdough

Clíona M. Reeves
November 11, 2008
Written by Clíona M. Reeves
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In a market where “low-carb” is still getting a lot of popular press, and low-carb diets such as South Beach are still going strong, the bakery industry has a tough battle to fight for consumers’ attention. Conventional wisdom commands that those who want to maintain – and especially lose – weight should eliminate carbs of all kinds from their diets permanently.

Fortunately, there is surprisingly good news for bread lovers, especially those who delight in the tang of sourdough bread.

According to Dr. Terry Graham, professor and chair of the department of Human Health and Nutritional Sciences at the University of Guelph, the kind of toast you have for breakfast can affect how your body responds to lunch. In an extensive research program funded by the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) and now entering its fifth year, Graham and his research team have been investigating the health benefits of various kinds of bread, particularly the effect they have on blood sugar levels.

The study involved 10 overweight men between the ages of 50 and 60. They were given four different kinds of bread – white, whole wheat, whole wheat with barley, and sourdough white bread – and their levels of blood sugar and insulin were measured.

One would expect that the whole-wheat varieties would show the healthiest response, but this was not the case.

“With the sourdough bread, the subjects’ blood sugar levels were lower, with a similar rise in blood insulin,” Graham says. “What was even more interesting was that this positive effect remained during their second meal and lasted even hours after.”

And subjects did not have to eat additional bread at the later meal for the benefits to persist.

“Athletes might recognize this as muscle memory,” he explains. “After learning how to run downhill and doing it over and over, using muscles as brakes, you diminish or eliminate the muscle pain afterwards. Likewise, when the gut encounters food, it releases incretins: hormones which tell the pancreas, which produces insulin, ‘Look out, here it comes!’

“That the marked difference in blood sugar and insulin levels persisted beyond the second meal suggests that eating healthfully is partially conditioning the gut to emit healthy responses. This suggests that the gut has a memory and can be trained. Small wonder, then, that the gut should sometimes be called ‘the little brain.’”

The reason for this effect is not known for certain, but is probably the way the fermentation of the sourdough changes the starches in the bread, increasing its health benefits. Unlike most breads, which are leavened with yeast, sourdough bread is leavened with a “starter” bacterial culture that begins the fermentation process, giving the bread its familiar sourdough tang. If you read Stuart McLean’s story “Sourdough” from Home from the Vinyl Cafe, you will recall how Dave is asked to baby-sit his neighbours’ precious, generations-old sourdough starter, you will get a taste of how far back this traditional bread-making method goes.

Even more surprising than the result that sourdough white bread scored best in the study was that both whole-wheat varieties (with and without barley), scored lowest – even below white bread! Subjects consuming the whole-wheat breads had huge spikes in blood sugar levels, and those levels remained high until well after lunch. This comes as something of a shock to those of us who have been dutifully consuming whole-wheat bread and bypassing all white varieties, including sourdough, in the belief that we were making the healthier choice.

This unwelcome high spike in blood sugar levels after eating whole-wheat bread appears to be due to the way in which whole-wheat bread is made.

“The milling process involved in making the whole-wheat bread used in the study is similar to that used for white bread,” Graham says. “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. Based on the findings of this study, as well as a follow-up study using whole grain rather than whole wheat, we are learning that the best way to get these nutrients is through a whole-grain bread, not whole wheat.”

Following up on this work, Graham’s team is conducting a series of related studies, one involving the effect of the different levels of available carbohydrates in different varieties of bread. First, subjects are given enough bread to add up to 50 grams of available carbs, and then are tested for blood sugar and insulin levels. By comparison, they are then given equal amounts of bread (whose carb count will naturally vary) and are tested.

“When you make toast or a sandwich, you don’t gear your meal to calculate grams of available carbs,” Graham notes.

Looking further down the road, Graham’s team is also conducting a long-term intervention study involving 24 men and women, half of whom are “healthier” in terms of weight, blood pressure and cardiovascular markers, and the other half of whom have elevated levels of each. Comparing commercial white bread and whole-grain sourdough, each subject will consume one type of bread for six weeks, then return to their normal diet, then spend six weeks consuming the opposite bread type. Throughout, their blood sugar and insulin levels will be measured in a battery of tests – an enormous undertaking.

“This is a huge research program comparing a whole range of breads,” Graham says. “It would be impossible without the financial support of the Ontario Ministry of Agriculture and Rural Affairs, and the interdisciplinary research team we have assembled, including University of Guelph colleagues from my own department of Human Health and Nutritional Sciences and the department of Food Science, from Phillip Lee Wing’s Food Development Group, and Stonemill Bakehouse in Markham, Ont., who worked with us to develop the sourdough bread we are using in our study. This large-scale, multi-phase research program is exactly what is needed to gather information that can be of real benefit to the health of consumers. Our goal is to complete work on this phase of the study in the next six months, and we’re also beginning a study involving people with Type 2 diabetes.”

For more information:
University of Guelph:  www.uoguelph.ca
Dr. Terry Graham:  www.uoguelph.ca/hhns/people/faculty/graham.shtml
OMAFRA:  www.omafra.gov.on.ca
Stonemill Bakehouse:  www.stonemillbakehouse.com
Food Development Group:  www.fooddevelopmentgroup.com.

Clíona M. Reeves, MA, is a freelance writer based in southern Ontario, and thinks a spot of toast would go down well right about now.

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