Today lets discuss another article that relates to the effect that our individual gut microbiomes have on how our bodies process nutrients. The work surrounding the microbiome is typically focused on defining what makes a "good" one, or a "bad" one. The research we discuss today doesn't do any of that, it actually probes an interesting topic. Bread.
Well thats it, you are likely thinking, justtryme90's life must be really boring if he thinks BREAD is an interesting topic. You just might be right! Nevertheless this is a topic that is relevant to many of us, because bread is a very popular food.
Today we will dive into some work published in the journal Cell Metabolism titled "Bread Affects Clinical Parameters and Induces Gut Microbiome-Associated Personal Glycemic Responses"
Bread and The Glycemic Index
Bread, it sure makes up a lot of the human diet. Estimates place it somewhere around 10% of our total caloric consumption! [2].
Bread is high in carbohydrates and as such it has the potential to have a pretty big impact on our blood sugar levels. As type II diabetes is becoming more and more pervasive in society, many of us must keep track of our blood sugar levels and try to eat more foods that have less of an impact. To assist in this many people turn to what is known as the glycemic index. This is just a number assigned to a food which tries to predict the effect that food will have on blood glucose levels. As maintaining a controlled post eating blood glucose level makes it significantly less challenging to mitigate diabetic symptoms.
Despite bread being a high carbohydrate food, we are told that not all bread is created equally. You hear all over the place that white bread is much worse for blood sugar then whole wheat bread. White bread is assigned a glycemic index number of 73/100, while whole wheat ranges from 71 down to 51.[3] The logic behind this lower assignment for glycemic index, is that whole wheat bread contains a lot of fibrous material, and as such should slow the absorption of sugars by our bodies.
So based upon these numbers we should assume that yes, white bread is worse for blood sugar than whole wheat! Whole wheat has a lower glycemic index! Duh, you dummy, why even ask this question? Tch, what an idiot this guy.
But Wait... Didn't You Mention New Research and Microbiome?
That's right, you can set your pitch forks down for now. We've some new research to discuss. In the study that I brought up the researchers were looking at the effects that consumption of either whole wheat sourdough (yum) bread or refined flour white bread (less yum...) had on various aspects of participants body biochemistry and their microbiomes.
What they report is surprising
The researchers had 20 participants, half supplemented their diets with only white bread, and the other half with only the whole wheat sourdough bread. What they found was that with regards to glycemic control (effect that the two types of bread had on the participants blood sugar levels, based on an oral glucose tolerance test there was NO difference.
Wait a minute... what?
The researchers also looked for changes in microbiome composition between the two groups. What they found was that the white bread eaters had an increase in the amount of a gut bacteria called Eubacterium ventriosum while the whole wheat sour dough eaters did not. Eubacterium vertriosum, the authors report, produces a fatty acid called butryate which is thought to be protective against colon cancer [4]. So white bread ...leads to more bacteria that protect against colon cancer then wheat bread...
Wait... What?
So all of that data pertains to the averages from the two groups, the authors then also looked for trends inside of each group. This is where things get even more interesting.
Different People Respond To White or Whole Wheat Bread Differently
What they found was that, inside of the two sample sets (those who ate white bread, and those who ate wheat bread), that some individuals maintained a very good blood sugar levels after eating the white bread, while others did not. The same was true for the whole wheat bread, some had good blood sugar levels while others did not. This result makes no sense if we just rely on the glycemic index, because that indicates that a person should not have a better tolerance to white bread over whole wheat sourdough. Nevertheless, 25% of the participants in the study DID.
Is The Microbiome Involved?
They then wanted to know whether or not there was some difference in the microbiome of individuals that made them better able to process white bread, or the whole wheat sourdough bread. What they found was that by looking at the microbiome composition of the individuals that they could predict, whether or not they would better respond to white or whole wheat sourdough, reporting that two bacteria are the determining factors: Coprobacter fastidiosus and Lachnospiraceae bacterium 3_1_46FAA. What they do not know as of yet is WHY these bacteria lead to the observed results.
Conclusions
The glycemic index is not a good predictor for how white or whole wheat bread will effect the blood sugar of an individual, and the bacteria that live in your gut do play a role in this process.
White bread is not necessarily worse for blood sugar then whole wheat bread, in fact for some people, it's better.
Sources
- http://www.cell.com/cell-metabolism/pdf/S1550-4131(17)30288-7.pdf
- https://www.ncbi.nlm.nih.gov/pubmed/26590418
- http://healthyeating.sfgate.com/whole-wheat-bread-good-blood-sugar-3955.html
- http://jn.nutrition.org/content/134/2/479.long
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