News: Don't Believe That Whole Wheat Is Healthier — Your Gut Bacteria May Think Differently

Move over whole wheat — white bread may be back in style after a new study shows that it may be your gut microbes that decide what kind of bread is best for you.

As a health food, whole wheat bread undeniably rules, right? With its whole grain goodness, whole wheat has long been touted as the better-for-your-body option, leaving its refined cousin as the behind-closed-doors choice for those with a love of the deep, soft chew conferred only by white bread.

If your preference of bread products runs to refined grains, we have the research for you. In a study published in Cell Metabolism from the Weizmann Institute in Israel, scientists took a closer look at what whole and refined grains truly mean to your gut microbiome.

The Backstory on Bread

Cultivated for about 10,000 years, wheat as an ingredient comes to us from Neolithic forebears who combined dry ingredients, including wheat and other whole grains, to create a core component of the everyday human diet — bread.

By wafting through human cultures for millennia, bread has arguably developed right along with the human gut microbiome. By "microbiome," we are talking about the ecosystem of bacteria, fungi, viruses, and other micro-critters that help us digest food, maintain a strong immune system, and get the most out of the nutrients we eat.

This month-long, randomized study evaluated the impact of traditionally prepared whole wheat sourdough bread and industrial, processed white bread, on the microbiota of 20 healthy volunteers. Basic differences between the grains include:

• Including the bran and germ, "whole" wheat is a plant product that has not been significantly processed to remove either its fiber or nutritional bounty. This study used whole wheat sourdough bread made for the study and delivered fresh to participants. The fermentation process of sourdough relies on "wild yeasts" and bacteria, instead of the baker's yeast that has become common in the last 150 years.
• Refined grains have been milled to a finer texture, resulting in the removal of hardier components, and a loss in nutritional profile. Refined white flours are usually enriched with vitamins and minerals to replace those lost during processing.

The study was composed of two periods when participants were supplied a standardized diet, and two periods when they were not. Meals were designed to have 50 grams of available carbohydrates. To accommodate for differences, participants consumed either three meals with 110 grams of white bread or three meals of 145 grams sourdough bread. The study subjects also used real-time diet logging with a smartphone app.

The research team analyzed glucose levels, used DNA-sequencing for stool samples, and applied modeling techniques to understand the abundance of gut microbiota in individual study participants. With regard to specific bacteria species, some of the findings included:

• The bacteria species Eubacterium ventriosum and the Anaerostipes genus significantly increased in abundance for those who consumed white bread. Earlier research has suggested compounds produced by these species protect against colon cancer, obesity, and reduce inflammation. Overall, big differences in function of the gut microbiome in participants eating either kind of bread were not observed.
• Small — but not clinically significant — changes were observed simply with the consumption of bread of either kind. The bread diet decreased levels of minerals like iron, calcium, and magnesium, and increased the level of lactate dehydrogenase, an enzyme produced by the body as a result of tissue damage. These were small changes, but are useful for developing a larger clinical profile of interaction of food in the human body.
• No big changes in diversity in the gut microbiome were observed. A senior study author, computational biologist Eran Segal, noted in a press release: "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."

Despite the lack of substantial differences, researchers continued to probe, suspecting that the generalization of the data across the study might have flattened out individual differences — and this turned out to be the case. In looking at data individually, about half of all participants (no matter which bread they were eating) had a lower glycemic response to their diet. A higher glycemic response is associated with elevated blood sugar, and can increase risk of diabetes, weight gain, and heart disease. This means that in the bodies of about half the participants, refined bread was a healthier choice, and for the other half, whole wheat.

Another senior author, Eran Elinav, remarked:

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. To date, the nutritional values assigned to food have been based on minimal science, and one-size-fits-all diets have failed miserably. These findings could lead to a more rational approach for telling people which foods are a better fit for them, based on their microbiomes.

The surprising finding of this study is that the "healthy" bread for you, and the bacterial friends that reside in your gut could be refined bread — or it could be whole wheat. Maybe the reason you love fresh white bread may be because your gut microbiome processes it as a nutritionally a better choice for your body. Basically, just eat whatever bread you like and don't worry too much about whether it's white or wheat.

Medical science is slowly moving toward personalized medicine. This study supports the idea that individual foods are interpreted — and utilized — by different bodies in different ways. Wholesale statements about what type of food is "good for you," may not hold true for everyone.

"Our study underlines the importance of personalization in dietary recommendations, as even the straightforward comparison of breads commonly considered 'healthy' and 'unhealthy' revealed personal effects," the authors write, which may suggest that "universal dietary recommendations may have limited efficacy."

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