This month I am discussing some new, exciting research on the effect of probiotics on the gut-brain axis(1). Before proceeding, I think it is best to explain the relationship between the intestines and the brain.

We have all experienced the effect of this axis. Most of us have been in a situation where we become very anxious about an upcoming event – making a presentation, taking an exam – and, as a result, developed a terrible gut pain or “knot.”

As quickly as the pain surfaced, it similarly eases when the stressful event resolves. When this happens, we don’t develop an ulcer or any other structural intestinal problem. So what physically happened to cause this pain?

The brain releases chemicals that travel through the blood stream (or nerves) to the gut.  The major nerves between the brain and intestines are called the vagus and the sympathetic nerves. The “knot” commonly experienced during stressful events is a result of the nerve endings releasing chemicals that cause spasms of the intestines and activation of the intestinal pain fibers.

Now, let’s get really geeky to explain how this happens in more detail. The gut-brain axis consists of:

(1) Vagus and sympathetic nerves that send messages to:

  • Stimulate or inhibit stomach and intestinal secretions
  • Increase or decrease stomach and intestinal motility
  • Enhance or decrease appetite
  • Transmit pain sensation from the gut to the brain
  • Alter our mood …positively or negatively

2) Hormones secreted by the brain and gut that stimulate or suppress the hunger and satiety centers in the brain affecting dietary intake. It is very common for people to attribute weight loss to stress. Their appetite seems to have just “disappeared.”

What really happened was that the emotional stress sent hormones and nerve signals to the intestines causing the following:

  1. Disruption of the healthy intestinal balance of the bacteria.
  2. Multiplication of the unhealthy bacteria, causing intestinal inflammation.
  3. Release of chemicals by the inflamed intestines, stimulating the satiety center in the brain – resulting in loss of appetite.
  4. Once the stress is resolved, both the healthy bacteria and appetite will return.

Be Happy…Take a Probiotic!

With this brief background, we will explore more clearly how intestinal bacteria can be impacted by stress and how probiotic bacteria can improve our mood. It is a two way street.

A research article published this month in the prestigious medical journal Proceedings of the National Academy of the Sciences discusses how probiotic bacteria may lessen anxiety and depression and help to maintain a positive attitude(3).

The point of the study was to determine how bacteria dwelling in the gut can effect the brain, and thereby influence mood and behavior. Since there are special neurotransmitters in the brain that impact mood, the researchers sought to evaluate whether these receptors could be modified by probiotics.

The researchers split their rodent subjects into two groups. One lot was fed a special broth containing Lactobacillus rhamnosus. The other group was fed an ordinary diet not fortified with microbes.

The mice were subjected to a battery of tests that measured their emotional state. The results indicated that the mice fed Lactobacillus performed more activities in a maze which indicated confidence and less anxiety. They were able swim in a container farther indicating a more positive mood.

Direct measurements of the animals’ brains supported the behavioral results. Levels of cortisone, a stress hormone, were significantly lower in the bacteria-fed mice than they were in the control group.

In addition, the number of neurotransmitter receptors was higher in the mood altering portion of the brain. Stimulation of these receptors results in sensations of relaxation and euphoria.

Finally, to prove that the vagus nerve is responsible for transmitting signals from the gut to the brain, the study was done again. But in the second study, the vagus nerve was severed in both groups of mice. The results of the repeat study revealed that the behavior in the two groups of mice was the same. The probiotic fed mice didn’t demonstrate the same activities which had been associated with confidence, less anxiety and a more positive mood. The damaged vagus nerve couldn’t transmit the benefits of the probiotics to the brain.

At this point you may say “well that is very interesting but we are not mice.  Are there studies in humans that also show similar results?”

A recent study in the British Journal of Nutrition(4) assessed whether a daily dose of a Lactobacillus and Bifidobacterium probiotic taken for 30 days could influence the psychological impact of everyday life events in normal human volunteers.

By using standardized psychological tests, the scores of the probiotic treated group had lower values for depression, anger-hostility and physical complaints.

The authors concluded that the beneficial effects of the probitotics may be explained by competitive exclusion of harmful gut bacteria and a decrease in inflammatory signals via the vagus nerve to the brain!

Take Home Message

If you are feeling a little “blue” or just want to feel positive about life, consider taking a beneficial probiotic like EndoMune. The best part of these studies is that there were no adverse effects of probiotics – no need for a black box!

References

(1) Gut-brain axis. Romijn JA, Corssmit EP, Havekes LM, Pijl H. Curr Opin Clin Nutr Metab Care. 2008 Jul;11(4):518-21.

(2) The new link between gut-brain axis and neuropsychiatric disorders. Fetissov SO, Déchelotte P.Curr Opin Clin Nutr Metab Care. 2011 Sep;14(5):477-82.

(3) Ingestion of Lactobacillus strain regulates emotional behavior and central GABA receptor expression in a mouse via the vagus nerve. Bravo JA, Forsythe P, Chew MV, Escaravage E, Savignac HM, Dinan TG, Bienenstock J, Cryan JF.Proc Natl Acad Sci U S A. 2011 Sep 20;108(38):16050-5.

(4) Assessment of psychotropic-like properties of a probiotic formulation (Lactobacillus helveticus R0052 and Bifidobacterium longum R0175) in rats and human subjects. Messaoudi M, Lalonde R, Violle N, Javelot H, Desor D, Nejdi A, Bisson JF, Rougeot C, Pichelin M, Cazaubiel M, Cazaubiel JM. Br J Nutr. 2011 Mar;105(5):755-64.