- The effects of whole grains in bread on human health seem contradictory.
- A randomized trial which compared processed white bread and artisanal whole wheat sourdough found no difference in parameters.
- Different people have different glycemic responses to the same diet due to the presence of their gut microbes.
Bread makes up roughly 10% of the adult caloric intake and is a staple for many regions around the world. A wide variety of breads are used, some of which are made using whole grains
are considered healthy. But are they, in fact, healthy?
The Making of Bread - What goes into it?
The most commonly used cereal for making bread is wheat. It is used either in the form of refined flour or whole wheat flour.
‘Consumption of white or wheat bread, really does not make a difference in the glycemic response, nor on the impact it has on health, as long as the intestinal microbiota is healthy.’
The outer layer of the wheat contains germ and bran, which contain dietary fiber, B vitamins, iron, magnesium, and zinc. So the addition of wheat as a whole grain in the diet is considered healthy, although the portion containing the fiber, gets removed during the milling process of refined flour.
Baker's yeast (Saccharomyces cerevisiae
) is a widely used leavening agent introduced in the process of bread making, about 150 years ago. Prior to which, sourdough was used for the same purpose. Sourdough contains a culture of mostly wild yeast, as well as lactic and acetic acid bacteria that naturally inoculate bread dough.
Sourdough fermentation releases several compounds that induce beneficial effects on glucose metabolism and increase mineral bioavailability.
White Bread Compared with Sourdough-leavened Wheat Bread
Many studies which that debated of healthier types of bread produced contradictory results; it is therefore not clear on the effects of bread on clinically relevant parameters and on the microbiome.
The Weizmann Institute scientists compared two kinds of bread, the white and the sourdough-leavened bread. The industrial white bread made from refined wheat is considered less healthy, as it is made with refined flour, yeast, food preservatives and emulsifiers.
Sourdough-leavened bread made in an artisanal bakery from freshly stone-milled whole grain wheat flour, and baked in a stone hearth oven was assumed to possess superior properties.
Two groups of 10 participants each were asked to consume large quantities of bread (supplying about a quarter of their caloric intake) for a week. One group had white bread and the other had sourdough-leavened bread. Following a break of two weeks, the group that had previously consumed white bread were given sourdough bread, and vice versa.
Wake-up glucose levels, several markers for inflammation and tissue damage, levels of the essential minerals such as calcium, iron, and magnesium, fat and cholesterol levels, as well as kidney and liver enzymes were measured. The makeup of the participants' microbiomes before, during, and after the study was also assessed.
"The initial finding, and this was very much contrary to our expectation, was that there were no clinically significant differences between the effects of these two types of bread on any of the parameters that we measured," said, Eran Segal, one of the study's senior authors. "We looked at a number of markers, and there was no measurable difference in the effect that this type of dietary intervention had."
Glycemic Response Has Individual Difference
The effects of whole grains in bread on human health, is contradictory, perhaps, because of the variability stemming from differences in bread ingredients, additives, the proportions in which they are used, and preparation methods.
Postprandial glycemic response (PPGR) is one way in which bread exerts its metabolic effects. PPGR is the elevation of blood glucose levels after a meal.
PPGR is an independent risk factor for cardiovascular disease and liver cirrhosis
It is also associated with obesity, markers of glycemic control and all-cause mortality in both Type 2 diabetes
Different people have different glycemic responses to the same diet. The glycemic responses of some of the subjects in the study were better to one type of bread, while others responded better to the other type.
Gut Microbes Play a Crucial Role
"The findings for this study are not only fascinating but potentially very important, because they point toward a new paradigm: different people react differently, even to the same foods," says Eran Elinav, a researcher in the Department of Immunology at the Weizmann Institute and another of the study's senior authors. "To date, the nutritional values assigned to food have been based on minimal science, and one-size-fits-all diets have failed miserably."
The findings could lead to a more rational approach, to assess which foods are a better fit for people, on the basis of their microbiomes.
Avraham Levy, a professor in the Department of Plant and Environmental Sciences and co-author, adds a caveat to the study: "These experiments looked at everyone eating the same amounts of carbohydrates from both bread types, which means that they ate more whole wheat bread because it contains less available carbohydrates."
The research team then devised an algorithm to help predict how individuals may respond to the bread in their diets.
Tal Korem, who conducted the study, noted that the algorithm could help to predict who are likely to have high blood sugar after eating white bread, and who will have elevated blood sugar after eating the sourdough.
Also, the intestinal microbes are different in each individual and hence the difference in responses. The composition of the microbiome in the people whose response to white bread produced high blood sugar levels, differed from that of the people who responded to sourdough bread with high blood sugar.
Be it white or wheat bread, intestinal microbes influence the glycemic response in the body.
- Korem et al. Bread affects clinical parameters and induces gut microbiome-associated personal glycemic responses. Cell Metabolism, (2017) DOI: 10.1016/j.cmet.2017.05.002