Can Dietary Interventions Improve the Gut Microbiota?

People in the dairy industry appreciate bacteria. Without bacteria, cows cannot digest the complex carbohydrates that make up the bulk of their diets. Without bacteria, the impressive array of cheese and fermented milk products are not possible.

And now they can appreciate bacteria for the important role they play in human health. Microbes that colonize the human body (some are present even before birth) are essential for proper immune and physiological development and function.

Over the past 5 years, the NIH has invested heavily (time, money and resources) in the Human Microbiome Project, to understand the role of colonizing microbes in human health and disease. The emerging data shed some light on the impact of microbes on human physiology, and on associations between diet and distinct human microbial communities.

Questions explored in the vast array of studies on this topic include:

  • What microbes colonize the human body?
  • What do these microbes do?
  • What do the microbial communities look like? (Relative abundance, diversity, richness, evenness*)
  • Do communities vary with diet, age, body site, individual, interventions, disease states, etc.?

And of great interest to the functional food industry:

  • Can dietary interventions improve the gut microbiota to make people healthier or more resistant to disease?

What do we now know?

Findings have become available on the microbial diversity of the human microbiome from the oral cavity, skin, distal gut (stool), and vaginal tract of healthy people.

Some findings:

  • No one microbial colonization pattern exists among all healthy humans (even healthy individuals differ quite a bit from each other)
  • Microbial populations of the human infant are characterized by a high level of instability (Palmer, et al.2007).  By the age of ~2 years, microbial populations have generally stabilized and remain stable throughout adulthood, although changes occur in institutionalized elderly (Claesson et al. 2012).
  • Some diseases (e.g., diabetes, obesity, inflammatory bowel disease, irritable bowel syndrome and allergy) are characterized by microbial colonization patterns that differ from healthy controls (Bäckhed et al. 2012)

A high diversity of microbes colonizing the gut is associated with lower levels of obesity and inflammatory bowel disease (Turnbaugh et al., 2009).

But despite all these advances, researchers have not defined the composition of a healthy gut microbiota (Bäckhed et al. 2012).

How can the dairy industry utilize these findings?

The field today is replete with associations, but light on causality. We know, for example, that probiotics can impact the structure or function of the microbiota and that they can have health effects. What we don’t know is if the health effects are directly caused by the microbiota changes or are just associated with them.

A practical question remains for people interested in creating dairy products that can positively impact the human microbiota and thereby promote health:  what is the target? As stated above, researchers have not defined a healthy gut microbiota:

“A healthy microbiome, considered in the context of body habitat or body site, could be described in terms of ecologic stability (i.e., ability to resist community structure change under stress, or to rapidly return to baseline following a stress-related change), by an idealized (presumably healthier) composition, or by a desirable functional profile (including metabolic and trophic provisions to the host).” (Bäckhed et al. 2012)

“The uniqueness of each individual’s microbial community thus seems to be stable over time (relative to the population as a whole), which may be another feature of the human microbiome specifically associated with health.” (The Human Microbiome Project Consortium, 2012)

However, if we can define what healthy microbial patterns are, we can develop products (including probiotic products) to correct dysbiosis and reflect a healthier pattern or greater stability.

But until the structure or function of a healthy human microbiota is better understood, the industry will need to focus on specific human benefits. Conducting research that targets both a health endpoint and a microbiota endpoint will hopefully lead to bodies of information that can lead to conclusions on causality.

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*Evenness: Measure of relative abundance of taxonomic groups of microbes. A microbial community with similar numbers of dominant microbes (i.e., no one group overwhelmingly dominates the group) has a high level of evenness.  Abundance: The level of any one taxonomic group of microbes within a community.  Diversity:  The number and abundance distribution of distinct types of microbes in a community.  Richness: The number of different microbial species or taxonomic units.