Exploring the sense and nonsense of food and health

Bacteria Rule – How is That?

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Bacteroides biacutis—one of many commensal ana...

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Our intestines are colonized by about 500 to 1,000 different species of what is referred to as “gut microbiota”.  What do all these microbes do?  Escherichia coli (not the harmful species 0157:H7) can help with water reabsorption and produce some of the vitamin K we need.  For the last few decades, scientists have developed what is known as “germ-free” mice; i.e. their intestines are sterile.  By using these species of mice, Jeffrey Gordon at Washington University School of Medicine in St. Louis discovered that a species of Bacteroides, a common inhabitant of human guts actually triggered intestinal cells to turn on or turn off some 100 of the 35,000 genes in the cell’s DNA.  Some of these genes helped the mice absorb and metabolize sugars and fats.  All in all, this particular Bacteroides species and probably others helped to regulate the calories the body obtains from food and stores as fat.  In other words, they may help regulate weight.

A recent study has strengthened this theory.  It suggests that the type of “bugs” in our intestines may influence whether we are lean or tend to being overweight.  Previous research has shown that heavier mice have a different gut bugs than leaner ones.  The obese mice have more of a bacteria called Firmicutes and fewer  Bacteroides (both of which reside in the human gut).  In normal mice, the situation is reversed.

Jeffrey Gordon and colleagues this time used human microbiota and injected germ-free mice with samples of human feces from which the bacteria then began to live in the guts of the mice.  Then the researchers began altering the diets of the mice.  When one group was fed a typical American diet, high in fat and sugars, they tended to gain weight and grow more Firmicutes gut bacteria and fewer Bacteroides.  When mice were fed a low-fat diet, the composition of the microbiota reversed and the animals stayed thin.  So if it remains true for humans when your gut bacteria contain more Firmicutes, your body may digest calories in a way that leads to more fat storage.  After the bacteria were transplanted from a lean human donor, the colonies in the mice had a high proportion of Bacteroides and a low content of Firmucutes.   But within 24 hours after the mice were switched to a high-sugar, high-fat diet, the proportions of the two species were reversed.  When identical twins were studied with different weights, the heavier twin had more Firmicutes colonies than the leaner one had.

Gut Bacteria and Vitamins

Now a new study published in Nature has separated gut bacteria into three major types to explain why the uptake of medicines and nutrients varies from person to person.  The study looked at the gut microbiota of 39 people from Europe, the U.S. and Japan and found that categories were not dependent on location, age, gender or body mass index.

Oluf Borbye Pedersen, professor of Health Sciences at the University of Copenhagen, said in a prepared statement.  “We may have uncovered a new “biological fingerprint” on the same level as blood types and tissue types”.  Having one of the three types, which are characterized by a dominate genus of bacterium – Bacteroides, Prevotella, or Ruminococcus, might play a large role in determining how you metabolize food to what vitamins your stomach is good at formulating (those in the Bacteroides group, for example, had a gut environment that was better at making vitamins B2, pantothenic acid, and biotin; those in the Prevotalla group had more B1 and folate-acid-making bacteria).

How can we control our own gut bacteria?  No one knows at the present time, but these studies shed light on the  complex causes of obesity and diet.

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