Is a healthy stomach the key to happiness?

It’s beginning to seem that way. A healthy gut population of beneficial bacteria is increasingly being found to have not just physical but mental health benefits. In the latest study, researchers found that probiotics actually seem to chase away bad feelings.

It’s all about the “brain-gut axis”—the two-way communications network between the intestines and the brain that affects the nervous system, hormones and immunity. In previous research, a few small human studies had found that either probiotic supplements or probiotic-rich foods such as yogurt reduce stress, reduce anxiety or improve mood. What’s particularly interesting about the latest study is that it focused on the kind of bad moods that are linked with an increased risk for depression—even in psychologically healthy people. And anything that can help with depression and that is also totally safe, well, that’s exciting.


In the placebo-controlled, randomized study, researchers at Leiden University in The Netherlands assigned 40 healthy adults without mood disorders to take either a daily probiotic supplement or a placebo supplement for four weeks. Each probiotic supplement contained a mixture of bacterial strains known to be important for a healthy human gut, including Bifidobacterium and Lactobacillus. The placebo was basically starch. Before and after the four-week pill period, participants answered survey questions to gauge their moods as well as vulnerability to depression and anxiety.

The result: Participants who took probiotic supplements were less prone to “rumination”—the tendency to dwell excessively on negative events or feelings—and had less aggressive feelings when they did feel sad. That’s important, the study authors note, because a tendency to ruminate “is sufficient to turn mood fluctuations into depressive episodes.” And aggressive thoughts are associated with depression and the risk for suicide.


Does this study mean we can prevent depression by eating the right foods or taking the right supplements? We can’t know yet. It’s more than a stone’s throw to go from improved moods to actual prevention of depression or anxiety disorders. Frankly, we’re just beginning to understand the connection. In a way, that’s what makes it so fascinating—and promising. We have more to learn before health professionals can use specific probiotics as a way to help people protect themselves from depression—or to treat it. But that may be the future.

Nor was this study designed to answer the “how” question—but the researchers do suggest possible mechanisms based on research. One theory is that healthy gut bacteria increase blood levels of tryptophan, an amino acid that boosts brain levels of the mood-boosting chemical serotonin (which often are too low in people with depression). A second theory is that healthy gut bacteria make it less likely that toxins in the gut will “leak” out and activate inflammatory pathways that play a role in depression. The third theory is that gut bacteria may directly improve gut/brain signaling in ways that enhance positive emotions.

Whatever the mechanisms, it seems clear now that a healthy gut is good for the mind as well as the body. We already know probiotics have been shown to prevent or treat infectious diarrhea, traveler’s diarrhea, antibiotic-associated diarrhea, irritable bowel syndrome, yeast infections, eczema and other conditions. Now there may be a new benefit—more happiness and less risk for depression.

So go ahead and enjoy probiotic-rich foods such as yogurt and kefir, pickled vegetables such as kimchi and sauerkraut, tempeh and miso. If you choose to supplement, look for products that contain both Bifidobacterium and Lactobacillus acidophilus, which colonize the human gut and so may provide benefits even after you stop taking them, according to naturopathic doctor Andrew L. Rubman, ND, Daily Health News contributing medical editor.

Whatever you do, don’t just stop taking any medication that was prescribed by your doctor and start taking a probiotic supplement instead. If you have a mood problem that lasts more than two weeks, especially if it is interfering with your life, don’t put off seeing your doctor.