Everybody likes bread — the "staff of life." But not all breads are created equal. Terry Graham is a professor in the Department of Human Health and Nutritional Sciences at the University of Guelph in Ontario, Canada. According to Professor Graham, "There's an urban myth that if you want to lose weight, you shouldn't eat bread." So the professor set out to find out the truth about bread. And what he discovered is a bit surprising.
For the experiment, he lined up 10 overweight men and women. On different days, each of them ate 50 grams of white bread, whole wheat bread, white sourdough bread, or whole grain wheat barley bread. The 50 grams is about two slices of bread. Then for three hours after they ate the bread, he measured their blood sugar, insulin, glucose-dependent insulinotropic polypeptide (GIP), and glucagon-like peptide-1 (GLP-1) levels. Most everybody knows about blood sugar and insulin. High blood sugar and high insulin levels are bad. They lead to insulin resistance, metabolic syndrome, diabetes, and weight gain. Lower levels are better. But what about the other two?
GIP and GLP-1 are hormones that your body makes in the intestines after you eat carbohydrates. Their action is to stimulate the production of insulin. Lower levels of GIP and GLP-1 after eating a carbohydrate like bread would be a good thing. So here's what happened to all the blood levels after eating these various breads.
The lowest blood sugar response came after eating the sourdough bread. GLP-1 was also the lowest in the sourdough bread. Insulin levels remained the same in all the breads which indicates that the sourdough bread actually resulted in greater insulin sensitivity. That's good! That's the kind of thing that can prevent weight gain and metabolic syndrome. Apparently the fermentation of the sourdough changes the nature of the starches in the bread so that they have a different effect in the body than regular bread. But that wasn't all they found.
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Not only was the sourdough bread better in terms of sugar and insulin response, but eating it also affected the next meal. The GIP levels were lower even after the second meal — and that effect lasted hours. In an interview Professor Graham stated, "This shows that what you have for breakfast influences how your body will respond to lunch." After working with overweight people for decades, I can say with assurety that eating a large, high protein, zero carbohydrate breakfast is one of the best aspects of any weight loss program. It has a strong influence on your appetite and how you eat the rest of the day. And then there is the surprising finding about whole wheat bread.
Most people think of whole wheat bread as being a much better choice than white bread. But it turns out that that is not the case. The sugar and insulin responses after eating whole wheat bread were actually worse than for white bread. Why is that?
According to the professor, the poor responses from whole wheat are probably 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. That is not the case with whole grain breads. He added, "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 whole grain bread, not whole wheat."
You can buy whole grain sourdough bread. You also can make your own. It seems to me that this would be the best overall bread choice to make. But don't forget that just because it does it less than white and wheat breads, it still raises blood sugar, insulin, GIP, and GLP-1 levels. So don't go overboard.
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Najjar AM, Parsons PM, Duncan AM, et al. The acute impact of ingestion of breads of varying composition on blood glucose, insulin and incretins following first and second meals. Br J Nutr. 2009 Feb;101(3):391-8.
Sourdough Bread Has Most Health Benefits, Prof Finds. July 07, 2008 - News Release from The University of Guelph. http://www.uoguelph.ca/news/2008/07/sourdough_bread.html. Accessed 5-25-14.