Findings reveal highly individual and unpredictable blood-sugar effects; your gut bugs likely rule your response to both kinds of bread
Bread is an ancient food, with roots in the Middle Eastern cradle of civilization.
And in most Western countries, bread occupies a special place in people’s hearts and kitchens.
Throughout Europe and the Americas, many people get about one-tenth of their calories for bread.
European aristocrats once disdained whole-grain, “black” bread as inferior peasant fare, preferring the “pure” appearance of white bread.
Ironically, white bread is now disdained by affluent folks for its squishy texture, bland flavor, and lower fiber and nutrient levels.
Now, intriguing clinical results from Israel reveal that whole-wheat bread isn’t always healthier on one critical measure: effect on blood sugar levels.
First, let's quickly cover a few basics about white and whole-wheat bread — and some critical but little-known distinctions between them.
Grains appear healthful for most people, in moderation
Fast-growing evidence suggests that low-carb, high-fat/protein diets enhance people’s metabolisms — thereby reducing the risk for diabetes, obesity, and cardiovascular disease.
But despite the claims of some best-selling authors — often based on notably thin or exaggerated evidence — occasional enjoyment of whole-grain bread is not a health threat to most people.
In fact, there’s loads of evidence that — for most people — whole grains and whole grain breads promote heart and overall health.
Needless to say, if you suffer mysterious symptoms that can’t otherwise be explained, it makes sense to try dropping gluten-containing grains like wheat to see if that improves matters.
What makes whole-wheat bread healthier?
The process of making white flour reduces — among other things — the levels of B vitamins, antioxidants, and minerals found in whole wheat berries and flour.
That’s why white bread is now fortified with iron, B vitamins, and sometimes with calcium, although that’s optional.
Fortification of white flour and bread — which started regionally in the 1920s and spread nationwide in the 1950s — virtually eliminated B-vitamin deficiency diseases such as pellagra.
Still, compared with unbleached whole-wheat flour or bread, fortified white flour and bread has significantly less fiber, protein, vitamin E, antioxidants, and trace minerals (magnesium, manganese, potassium, and zinc).
Whole wheat beats white for antioxidants
Canadian scientists compared the antioxidant content of whole-wheat flour and bread versus white flour and bread, as well as the antioxidant power they displayed in the test tube (Yu L et al. 2013).
Whole grains provide substantial amounts of antioxidants, it’s no surprise that whole wheat flour has significantly more of them compared with white flour, and shows significantly higher antioxidant activity.
Also, unsurprisingly, the bread-making process (before baking) cut the antioxidant content of whole wheat and white breads by 28% and 33%, respectively.
Interestingly, baking of the two types of bread — which apparently released certain antioxidants from inside indigestible fibers — raised the antioxidant capacities of whole wheat and refined flours by 1.8 and 2.9 times, respectively.
As the Canadian team concluded, “Whole wheat flour and bread were superior to refined flour and bread in in vitro [test tube] antioxidant properties.”
Israeli study compared white to whole-wheat sourdough
The new clinical study comes from scientists at Israel’s Weizmann Institute.
The researchers set out to compare breads normally viewed as lying on opposite ends of the health spectrum.
The 20 people recruited for the study normally consumed about 10% of their calories from bread.
Before and throughout the trial, the researchers measured various aspects of health:
- Cholesterol levels.
- Kidney and liver enzyme levels.
- Glucose levels upon awakening.
- Calcium, iron, and magnesium levels.
- Standard markers for inflammation and tissue damage.
Importantly, the investigators also analyzed the participants’ microbiomes — that is, their gut- bacteria profiles — before, during, and after the study.
The participants were divided into two groups and assigned to eat different breads:
- White bread made industrially from refined/bleached wheat flour.
- Whole-wheat sourdough made from freshly stone-milled whole grain wheat flour.
The whole-wheat sourdough was specially made for the study by an artisanal bakery, using a stone hearth oven.
All the participants were asked to consume even more bread than usual — about a quarter of their caloric intake — for one week.
After a two-week break, they switched places: the white bread group ate the sourdough bread, and vice versa, for one week.
So the trial was designed for every participant to consume the same amount of digestible carbs from both bread types.
When participants were eating whole-wheat sourdough, they were assigned to eat more of it compared with the assigned amount of white bread — because whole wheat has fewer digestible carbs and more indigestible fiber.
Unexpectedly unpredictable effects on blood sugar
When the scientists compared the effects of the two types of bread on blood sugar, they were shocked by what they found.
Only about half of the participants had higher blood sugar levels after eating white bread, while the other half had higher blood sugar levels after eating the whole-wheat sourdough.
“We were sure that the sourdough bread would come out a healthier choice, but much to our surprise, we found no [consistent] difference between the health [glycemic] effects of the two types of bread,” said Eran Segal, Ph.D., a lead co-author of the study.
“That’s probably because the body’s response to bread is a highly personal matter, so the differences between people in the study averaged themselves out,” added co-author Dr. Eran Elinav.
And it looks as though differences in the participants’ intestinal microbes — their gut microbiomes — were responsible for these unexpected responses.
The microbiomes of those whose blood sugar spiked in response to white bread differed from the those of the people whose blood sugar spiked in response to whole-wheat sourdough bread.
The scientists developed an algorithm that predicts a person’s response to the two very different types of bread based on the composition their microbiome.
This kind of research raises the possibility that in the future, people could have their microbiota analyzed to alert them to foods that may produce adverse effects.
“Using this algorithm, we managed to predict who will have high blood sugar after eating white bread, and who will have high blood sugar after eating the sourdough,” said co-author Tal Korem.
Sweet on sourdough
Starting in the 1970s, bakeries began making whole wheat breads, including sourdough varieties made, by definition, with fermented dough.
Mass-market white breads are made with yeasts that date back only to the 1860s, which were selected for their commercially advantageous properties.
In contrast, sourdough starter cultures have been passed down from ancient times, which may be why whole-food journalist/author Michael Pollan calls sourdough “the proper way to make bread.”
Some researchers speculate that sourdough breads are less likely to adversely affect the small but apparently growing proportion of people who appear truly gluten-sensitive without celiac disease.
(Gluten-sensitivy can be confused with sensitivity to fermentable starches called FODMAPS, found in many plant foods including grains, beans, fruits, greens, cruciferous veggies, garlic, and onions.)
Whole-wheat bread is still healthier than white
For sure, the new findings about highly individual blood-sugar responses to white and whole-wheat bread defy conventional wisdom.
Nonetheless, the other nutritional advantages of whole-wheat bread – more micronutrients, fiber and antioxidants – make it a clear winner over white bread.
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