I Have a Gut Feeling They're on to Something.

You know you're mostly not human, right?

When you count the microorganisms living in your gastrointestinal tract, skin, and respiratory tract will, there are ten times as many bacterial cells as human cells in your body.  We are ecosystems, rather than single organisms.  If 20th century nutrition was the discovery of vitamins, proteins, carbohydrates, and other nutrients, 21st century nutrition will be the study of how nutrients affect those 90% of nonhuman cells within us.

These friendly bacteria (also known as normal flora or probiotics) play an important role in our gastrointestinal health, allergies, normal immune system functioning, and maintaining a normal body weight.  Some intriguing early animal studies found that probiotics could even decrease symptoms of depression.  In the June issue of the journal Gastroenterology, researchers at UCLA published the first study showing a direct effect of probiotics on the human brain.  And no, this does not mean that people were shoving yogurt into their ears.

Researchers divided a group of 36 healthy women into three subgroups: the first received two servings of yogurt with probiotics daily; the second subgroup received non-fermented milk products; and the third subgroup received no special foods.

After four weeks, these women underwent psychological testing while in a functional MRI (fMRI) -- an imager that examines real-time brain activity, rather than just taking a static image.  The probiotic subgroup showed significantly reduced activity in brain areas associated with emotional variability and pain.  Translation?  Probiotics made them less moody!

The importance of this study is that it proves that gut bacteria can have a direct impact on human brain functioning, specifically in the areas of emotions and pain perception.  It did not examine what the exact mechanism of action is.  We also have to be a bit cautious with this study, because these were healthy volunteers, with no gastrointestinal or psychological disorders.

Nevertheless, this just adds another piece of evidence that indicates that tending to the complex "rain forest" within us, with fermented foods and lots of dietary fiber, is probably more important than taking high doses of any single nutrient.

Tillisch K et al.  Consumption of Fermented Milk Product With Probiotic Modulates Brain Activity.  Gastroenterology June 2013; 144(7):1394-1401.

Good Bacteria = Smaller Waistline?

Research in the area of normal flora -- the "good," or beneficial bacteria that live in our gut -- has been exploding in recent years.  It has been known for a long time that supplementing with probiotics (those friendly bacteria like Lactobacillus and Bifidus) can help with conditions ranging from eczema to allergies to irritable bowel syndrome.  But the list of benefits of proper microbial balance keeps growing -- and it seems like the more we know, the more we realize how much we don't know yet.

Recently, Chinese researchers (1) found a connection between the microbes in our gut and the problem of obesity.  Mice that were bred to be resistant to obesity, in spite of a high-fat diet, rapidly gained weight when injected with a bacteria from the human gut called Enterobacter cloacae.  They hypothesize that a harmful substance produced by these bacteria, called endotoxin, contributes to insulin resistance.  Insulin resistance is a major contributor to overeating and obesity, and the hallmark of type 2 diabetes.  Think of insulin as a key to open the door to your cells so they can take in blood sugar for energy; insulin resistance is where the lock on the cell doors gets worn and rusty, making it more difficult for insulin to do its job.  Insulin levels rise, which contributes to widespread inflammation in the cardiovascular system, and promotes fat storage.

In the same article, the researchers report a case study of a man who lost 66 pounds in 9 weeks by switching to a diet that promoted good bacteria growth in the intestinal tract.  The harmful Enterobacter was reduced to undetectable levels.

Now before you pop an acidophilus supplement or grab a Yoplait, expecting miraculous weight loss, we need to look a little more closely at the diet supplied to this test subject.  It was very high in fiber, to feed the good bacteria in the gut, and also included traditional Chinese fermented foods that might seem challenging to our palates.  Fermented foods are beginning to look more important than probiotic supplements, simply because of sheer numbers:  supplements might have anywhere from 1 billion to 20 billion bacteria per serving, which sounds like a lot, until you realize that there are about 100 trillion bacteria in your gut!  Traditional fermented foods have much higher levels of good bacteria than supplements.  We're not talking about most commercial yogurts, which are crammed with sugar and have questionable amounts of active bacterial cultures; we're talking about plain yogurt, kefir, miso, traditional sauerkraut, and kimchi, to name a few.

We've barely scratched the surface on research into our normal flora -- not just in the gastrointestinal tract, but also on the skin, respiratory tract, and genitourinary tract.  It makes sense that they would have such a huge influence on our health:  there are ten times as many bacterial cells as human cells in our bodies!  We are really more of an ecosystem rather than a single organism.  Perhaps in the future there will be much less emphasis on therapeutic nutrition, except as it applies to how it influences our flora.

1.  An opportunistic pathogen isolated from the gut of an obese human causes obesity in germfree mice.  The ISME Journal advance online publication 13 December 2012; doi: 10.1038/ismej.2012.153