How does changing your diet impact your gut microbiota? (+Week 6)
The takeaway
Getting “back on the wagon” with diet can be quite challenging
Recognizing our behaviors that leads to diet derailment is important for progress.
Shifts in diet can affect the gut microbiota and have health consequences
Understanding these shifts can help foster a more well-rounded view on our health
Read on for more!
After the weekend indulgences, it took considerable effort to get back on track with the diet. It always astonishes me just how quickly we can “fall off the wagon” so to speak. And just as I thought I had regained momentum, I derailed myself again. My choices were fairly wholesome, like bread, cow’s milk, cheese, almond flour pancakes, and nice chocolate. These foods are certainly not bad, but when they take the place of a high-fiber food like fruit or vegetables, there is an opportunity for improvement.
Also, I can feel the ill effects of consuming bread and cow’s milk pretty quickly. My stomach hurts, I get bloated and the mucus production in my sinuses picks up. Generally, I don’t feel this with products like Ezekial sprouted bread or cheese made with cow’s milk; however, I must always be mindful of not overdoing it even with these items. That’s the second part: for me, the slippery slope is pretty steep for me and once I fall, I usually fall hard. I tend to be all or nothing, so once I feel like I’m “off” my game, the door just opens up for additional less-nutritious or reactive foods to creep in my diet.
Certainly the behavioral psychology aspect of adopting a new eating style is fascinating topic; one that I think is often overlooked. I listened to a podcast with Melissa Hartwig, founder of the Whole 30, and she mentioned that we often think it’s about the food, but really it’s much more than that. We tend to focus primarily on what to eat and what not to eat, overlooking our behavioral habits that lead to certain food choices or altogether ignoring how certain foods make us feel. Or we even acknowledge those feelings, but forget them or choose not to honor them.
Anyhow, with the rapid unpleasant response my body has to certain foods, I wondered if and how my gut microbiota responds to a shift in dietary patterns. How much does my diet need to change for my microbial community to respond? How quickly does this happen? What are the potential health effects of dietary/microbial shifts? Does the microbiota ever shift back?
I found a few studies that assessed how gut microbiota changes in response to a shift in diet. I will summarize the studies briefly, then attempt to answer the questions I posed.
Study 1: plant-based vs. animal-based diet
One study [1] consisted of 10 people who ate one of two prescribed diets for 5 days. One diet was plant-based (rich in grains, legumes, fruits and vegetables) and the other was animal-based (meats, eggs, cheeses). Changes in the gut microbiota appeared 2 days after beginning the diet intervention. The volunteers consuming the animal-based diet had more substantial changes than those consuming the plant-based diet. The individuals eating the eat-based diet had increased bile-resistant bacteria, most notably Bilophila wadsworthia which is associated with inflammatory bowel disease [2].
The animal-based increased the amount of bacteria used to make cheese and sausage (Lactococcus lactis, Pediococcus acidilacteris and Staphylococci), suggesting that the bacteria in their food can impact the microbial community of the gut. The animal-based diet also reduced the production of two short-chain fatty acids, acetate and butyrate, which are associated with proper gut and immune function and lower inflammation.
Study 2: high-fat/low-fiber vs. low-fat/high-fiber diet
Another study [3] also recruited 10 volunteers, which consumed either a high-fat/low-fiber diet or a low-fat/high-fiber diet for 10 days. Before initiating the diet intervention, this study characterized the gut microbiota of these 10 volunteers plus 88 others and found that long term diet is associated with certain types of bacteria. People who eat more animal protein and saturated fats tended to have higher numbers of Bacteroides bacteria (Bacteroides enterotype). People who consume diets richer in carbohydrates and simple sugars, such as vegetarians and vegans, were enriched in Prevotella bacteria (Prevotella enterotype). The volunteers could be classified into one of two enterotypes, or groups, but they also had highly unique microbial communities. These patterns are corroborated by a separate study that compared the microbiomes of European children to native Africans [4].
They randomly selected 10 volunteers, all of which fell into the Bacteroides enterotype group. Changes in the gut microbiota appeared within 1 day of beginning the diet intervention. Although the gut microbiota changed, the bacteria that changed differed among the volunteers. Eating an identical diet could not overcome the high variability between volunteers. Overall, despite half of these volunteers eating a low-fat/high-fiber diet, they maintained the Bacteroides-dominant microbial community throughout the 10 day study.
Study 3: high-fat/low-fiber vs. low-fat/high-fiber
In this study [5] 20 African Americans and 20 rural South Africans switched their typical diets for 2 weeks. The African Americans switched from a typical high-fat, high-animal protein, low-fiber diet to a diet similar of the rural South Africans, which consisted primarily of high-fiber grains, plant proteins, vegetables and fruit. They collected samples prior to and 1 week after initiating the diet. Similar to the aforementioned study, prior to the diet intervention, the high-fat/low-fiber diet was associated with dominance by Bacteroides and the low-fat/high-fiber diet was associated by higher Prevotella.
Switching from the high-fat/low-fiber to low-fat/high fiber diet resulted in a decrease of bile acid production and of the bile-resistant bacterium B. wadsworthia. Additionally, the low-fat/high fiber diet resulted in higher production of the SCFA butyrate and higher numbers of the microbes responsible for butyrate production.
As expected, the opposite was true when switching to the high-fat/low-fiber diet: bile acid production increased and both SCFA production and SCFA-producing microbes decreased. Additionally, the high-fat/low-fiber diet resulted in increased prevalence of Fusobacterium nucleatum, a bacterium that has been shown to be enriched in human colon cancer tissue (although no direct link exists) [6].
Now onto the questions
How much does my diet need to change for my microbial community to respond?
The first study noted more substantial changes in the animal-based diet intervention, likely because going from a normal diet to one consisting only of meat, cheese and eggs is more drastic than going to a plant-based diet that includes vegetables, fruits, grains and legumes.
The second study did not specify the dietary breakdown.
The third study switched African Americans from typical western diet high in fat and low in fiber to high fiber, low fat diet similar to that of rural South Africans. Fat content decreased from 35% of calories to 16%, and fiber increased from 14 g to 55 g daily. The South Africans switched from their diet to a more typical western diet, increasing fat from 16% to 52% of calories and reducing fiber from 66 to 12 g daily.
How fast do changes in the gut microbiota occur?
Two studies noted changes within 1 or 2 days after a shift in diet, the other only measured after 1 week and noted changes at that time. One or two days is pretty fast!
What types of microbial changes are observed?
Eating more meat and fats results in increased bile acid production and bile-resistant bacteria, most notably Bilophila wadsworthia. Bile helps digest fat, so increasing dietary fat would lead to increased bile secretion, favoring the growth of bile-resistant bacteria in the gut. The opposite is also true.
Eating more carbohydrates and fiber results in increased SCFA production and an increase in the prevalence of microbes that produce SCFAs. The opposite is also true.
Bacteria that is ingested in food appears in fecal samples, so the microbes used to make cheese or sausage, or yogurt or sauerkraut, can impact the gut microbial community.
What are the potential health effects of these diets?
B. wadsworthia was enriched in the gut of the subjects consuming the higher fat, higher animal-protein based diets [1, 5]. It has been associated with inflammatory bowel disease or colitis [2]. One of its metabolic byproducts, hydrogen sulfide, is thought to contribute to inflammation of intestinal tissue [2]. Thus, the researchers suggest that an animal-based diet could contribute to the development of inflammatory bowel disease [1, 5].
Additionally, the high-fat/low fiber diets resulted in lower production of the short-chain fatty acids (SCFAs) acetate, butyrate and propionate. These SCFAs are the products of bacterial fermentation of undigested carbohydrates and are important to gut health and immune function. The decreased amount of SCFAs is likely due to the low fiber content of the high-fat and animal-based diets, which are limited in fermentable carbohydrates.
Does the microbiome ever shift back?
Yes, the microbial community and gut environment reverted back to the pre-intervention status upon resuming the normal diet. The change also occurred within the time frame studied, either a day, two days or a week.
Final thoughts
The ability of the gut microbiota to respond to our diets likely had important evolutionarily benefits, because our ancestors’ diet may have shifted drastically depending on what they could gather or if they had a successful hunt. Often, the changes in gut microbiota reflect the new gut environment, as in increased fat intake leads to more bile acid which selects for bile-resistant microbes, or more fermentable carbohydrates supports the growth of certain microbes that produce more SCFAs. Although changing the diet doesn’t necessarily alter the entire makeup of the gut microbial community, small changes can have health consequences.
It’s important to note that most people these days don’t drastically alter their diet like in these interventions. More studies are needed to delineate the full impact of diet on gut microbiota and the associated impact on health. However, we should be mindful that our gut microbiota do respond to the food we eat, and they can do so fairly quickly. So next time I want go on my “weekend free-for-all diet” I’ll consider my gut microbes first and understand that my diet will affect them as much as it affects me.
References
David, L.A., et al., Diet rapidly and reproducibly alters the human gut microbiome. Nature, 2014. 505(7484): p. 559-63.
Devkota, S., et al., Dietary-fat-induced taurocholic acid promotes pathobiont expansion and colitis in Il10-/- mice. Nature, 2012. 487(7405): p. 104-8.
Wu, G.D., et al., Linking long-term dietary patterns with gut microbial enterotypes. Science, 2011. 334(6052): p. 105-8.
De Filippo, C., et al., Impact of diet in shaping gut microbiota revealed by a comparative study in children from Europe and rural Africa. Proc Natl Acad Sci U S A, 2010. 107(33): p. 14691-6.
O'Keefe, S.J., et al., Fat, fibre and cancer risk in African Americans and rural Africans. Nat Commun, 2015. 6: p. 6342.
Kostic, A.D., et al., Genomic analysis identifies association of Fusobacterium with colorectal carcinoma. Genome Res, 2012. 22(2): p. 292-8.