Your gut contains 10 times as many microbial cells as there are cells in the rest of your body — around 100 trillion microbes (bacteria, fungi, viruses, etc.) from up to 5,000 different species.

These busy little organisms help you get energy from food; help manufacture neurotransmitters such as dopamine (involved with movement, pleasure, reward), serotonin (mood, sleep, appetite), and acetylcholine (muscle control, memory); and produce vitamin K2.

They're also important for healthy immune function and glucose regulation.

A landmark study in the journal Cell also showed that beneficial microbes (probiotics) reduce chronic inflammation that can lead to heart disease, diabetes, and dementia.

To keep your gut biome in balance and promoting good health, you want to eat probiotic-packed fermented foods. But not all fermented foods nurture beneficial gut microbes. Soy sauce, alcohol, and sourdough bread are fermented but they're not pro-biotics.

And when sauerkraut, kombucha, and kimchi are made shelf-stable (stored at room temperature), their probiotics are inactive. You want to select refrigerated products such as yogurt, kefir, unpasteurized kimchi, sauerkraut, and kombucha, that say "live and active cultures" on the label.

You also want to avoid heating miso if you're hoping for a biome boost, and dodge fermented products dosed with excess salt or added sugars.

Enjoying foods with active fermented cultures — as well as taking supplement-based probiotics that contain the acid-resistant species lactobacilli and bifidobacteria — will help you slow down the aging process.

Get additional good-for-your-gut advice in my book, "The Great Age Reboot."