A healthy digestive tract can improve your mood, calm anxiety, and maybe even fend off Alzheimer's disease.

Q: I've heard that the gut is the "second brain." What does that mean exactly? I mean I know I feel better when my digestion is working well, but is there more to it?

Believe it or not, most melatonin, the hormone in the body that promotes restful sleep, is not produced in the pineal gland, but in the small intestine. In fact, I have several colleagues who successfully use melatonin as part of a treatment strategy for a range of intestinal ailments-from IBS to Crohn's disease.

GABA, a calming neurotransmitter that is useful for anxiety and other mood disorders, is another natural brain chemical produced by bacteria in the gut. And we have long been aware of a genetic connection (trending in families) between various forms of schizophrenia and celiac disease.

Most pharmaceutical antidepressants work by making the brain think that we are awash in serotonin, the natural "happy" biochemical. Serotonin is produced both in the central nervous system, and in the gut from its amino acid precursor 5-hydroxy tryptophan (5-HTP), which is directly linked to a particular gut bacteria, Bifidobacterium infantis.

All to say, we keep discovering more and more connections between healthy digestion and a healthy mind.

Go Pro
According to David Perlmutter, MD, in his new book, Brain Maker, "much of what we know about the microbiome comes from studying so-called germ-free mice. These are mice that have been altered to not have any gut bacteria, thereby allowing scientists to study the effects of missing microbes, or conversely, exposing them to certain strains and watching what happens. Germ-free lab rats have been shown, for example, to have acute anxiety, an inability to handle stress, chronic gut and general inflammation, and lower levels of an important brain-growth hormone called BDNF (brain-derived neurotrophic factors). But these symptoms can be reversed once the rats are fed a diet rich in Lactobacillus helveticus or Bifidobacterium longum, two common probiotics."

Turns out that people with lower levels of BDNF have an increased risk of Alzheimer's disease. Could this mean that we can prevent Alzheimer's with probiotics? Research continues in this direction.

In the meantime, it's a very good idea to get more healthy bacteria into your diet-for the good of your brain, as well as your gut. One of my favorite ways to get probiotics is to eat some fermented food every day. Think about kimchi, sauerkraut, yogurt, kefir, or kombucha. I put some fermented food into my spinach-blueberry-based morning smoothie every day.

Natural Mood Boosters
In addition to keeping your gut happy with probiotics and an anti-inflammatory diet, there are other widely available natural substances that can help with mental and emotional well-being. I mentioned GABA (gamma-aminobutyric-acid) above as a calming neurotransmitter. The methylated form of GABA, called Phenibut, can help promote sleep and banish anxiety in nightly doses of 250-500 mg.

Other effective mood enhancers include 5-HTP in the 50-100 mg daily dose range and St. John's wort (900 mg daily). I recommend that anyone who suffers from mild-to-moderate depression try St. John's wort before considering pharmaceutical drugs. Often relief is palpable within 10 days.

Two cautions with St. John's wort: In general those with blood type O do not benefit much from this herb. They do better with a Paleo-style diet and amino acid therapy, such as 50-100 mg 5-HTP at bedtime. Also St. John's wort can cause a type of heat rash in people travelling from a low-sun to a high-sun environment (such as taking a tropical vacation). This is reversible-just stop taking St. John's wort while you're in the sun, and the rash will fade without residual problems.

Get Your Vitamins
B-vitamin deficiencies are a common cause of depression. Vegans, people who have difficulty absorbing the vitamin, and those with gut problems such as gluten sensitivity may be particularly at risk. The small intestine, where nutrients are absorbed into the blood stream, is finicky about letting substances deeper into the body, and the microvilli need to be in good shape to permit B-vitamin absorption. Most celiacs are deficient in B vitamins, especially B12.

High doses of niacin, or vitamin B3, have been successfully used by orthomolecular physicians for decades to cure severe mental illness. This therapy requires medical supervision with a nutritionally trained professional.

Another common nutrient deficiency that can cause depression, among other problems, is vitamin C. Unlike other mammals, humans do not produce vitamin C, so we have to get it from our diets. For this reason, I recommend supplementing with at least 1,000 mg of good-quality ascorbic acid every day for optimal health.

Science continues to discover more and more connections between healthy digestion and a healthy mind.