Page 44 - Today's Dietitian (March 2020)

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found that shifts from an omnivorous to the effect of a high-protein diet on total patterns seem to have the greater influ-
a plant-based diet altered gut microbi- gut bacteria. Obese men consuming a ence in determining what type of bacte-
ota composition in as little as five days. high-protein, weight-loss diet had a sig- ria is present.
When subjects ate an animal-based diet nificant decrease in total gut bacteria,
with very little carbohydrate or fiber, specifically butyrate-producing organ- Micronutrients and the Microbiome
gut bacteria shifted to be more similar isms. Researchers couldn’t determine The gut microbiome influences the
to that of other carnivorous mammals, whether the decrease in gut bacteria was body’s ability to use and absorb micro-
while the opposite occurred when sub- caused by the higher protein intake or by nutrients from food. The example of this
jects ate a plant-based diet. Consump- the lower carbohydrate intake. But upon connection that’s probably most familiar
tion of the animal-based diet resulted in examination of fecal metabolites, those to RDs is vitamin K. It’s routine to give a
an increase in bile-tolerant microbes and on the high-protein diets were shown to vitamin K injection to newborns at birth
a decrease in those able to ferment car- have an increase in certain compounds to prevent hemorrhage. Infants are born
bohydrates. The opposite was true when that indicate a shift to microbial protein with a low concentration of vitamin K–
subjects consumed a plant-based diet— fermentation. The metabolites result- producing bacteria in the gut and may
the type of microbes shifted to increase ing from protein fermentation have been not have an adequate supply for blood
carbohydrate fermentation. Based on correlated with an increase in inflam- clotting. Over time, gut bacteria are able
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the results of this study, it’s clear that mation and risk of colorectal cancer. to start producing adequate amounts of
both dietary patterns and diet modifica- The type of carbohydrate consumed vitamin K.
tions can affect the composition of the seems to have significantly different But the role of gut bacteria in micro-
gut microbiome relatively quickly. 12 effects on the gut microbiome. Humans nutrient status isn’t just limited to vita-
don’t have the enzymes to break down min K. Bacteria can synthesize vitamin
Macronutrients and the and digest many dietary carbohydrates, B 12, vitamin B 6, pantothenic acid, niacin,
Microbiome so gut bacteria may be beneficial by biotin, and folate. These various vita-
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The gut microbiome doesn’t only change using the fibers humans can’t digest for mins are either byproducts of fermenta-
with a shift from an omnivorous to a energy. A 2016 study by Sonnenburg and tion or are excreted by the gut bacteria.
vegetarian or vegan diet; modification colleagues evaluated the importance of The ability to produce these important
of macronutrient ratios also can carbohydrates that are easily digested vitamins may help humans maintain
influence gut microbes. However, it’s by microbes by studying germ-free adequate levels of them.
challenging to study the impact of a mice. The mice’s digestive tracts were The microbiome also affects the
specific macronutrient in isolation populated with a human fecal sample, absorption of certain minerals. For
because a decrease in one results in an and the mice were put on a high- or low-
immediate increase in another. carbohydrate diet. After seven weeks,
In general, those who consume a mice on the low-carbohydrate diet
high-carbohydrate diet tend to have an had 60% fewer microbial strains in the
enterotype, or bacterial classification gut compared with those fed the high-
that contains more prevotella, whereas carbohydrate diet. Other studies also
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those who eat a higher-fat or -protein found that low-carbohydrate diets lead
diet tend to have more bacteroides. Pre- to a decrease in certain types of gut
votella has been linked to improved bacteria, particularly those that produce
glucose tolerance but also to increased butyrate. These findings are significant
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inflammation. for human health because low levels
The type of fat in the diet also seems of butyrate-producing bacteria in the
to influence the type and function of gut have been linked to an increased
the gut microbes, but human research risk of inflammation and poor gut-
isn’t yet available. A 2015 animal study barrier function. The opposite also is
found that mice fed lard had increased true; a study of obese subjects found
inflammation markers, exacerbated by that a low-calorie diet including a fiber
gut bacteria, whereas those fed fish oil, supplement increased bacterial diversity
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which is higher in anti-inflammatory by 25%. This research suggests that
omega-3 fatty acids, showed lower carbohydrates in the diet encourage the
inflammation and less metabolic growth of gut-protective bacteria.
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dysfunction. The results of this study In summary, carbohydrates, particu-
likely are due to the ability of certain larly in the form of fermentable fibers,
gut microbiota to facilitate absorption seem to be beneficial. Also, the type of
of lipids by increasing the size and fat consumed also can trigger an inflam-
number of lipid droplets, which, in turn, matory or anti-inflammatory response
increases inflammation. within the gut microbiome. Although
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The impact of protein on gut bacte- the microbiome can be affected by
ria is unclear. A 2011 study evaluated short-term dietary changes, long-term

44 TODAY’S DIETITIAN • MARCH 2020