Actor Dolph Lundgren and Microsoft founder Bill Gates are both reported to have an IQ of 160 — making them exceptionally intelligent.

It would be interesting to know what microbes are lurking in their gut biome, because new research shows that specific bacteria have a direct impact on a person's mental function in middle age.

Looking at the gut biome of around 600 men and women ages 48 to 60, a study published in JAMA Network Open found that those who scored better on cognitive tests had a good balance of specific bacteria (Barnesiella and Lachnospiraceae).

How can you help those little powerhouses thrive in you? Well, they're positively associated with eating a plant-based, fiber-rich diet.

In addition, taking a probiotic with Lactobacillus rhamnosus helps keep them, and you, happy — especially if you’re feeling stressed. (Who isn't these days?)

That's what a Chinese study last year published in the journal Foods concluded after researchers looked at how the gut's microbial composition is associated with a person's perceived quality of life.

Ditch gut-damaging foods such as red and processed meats, added sugars and syrups, and highly processed foods.

Instead, adopt a plant-based diet that includes 100% whole grains, legumes, and seven-plus servings of fruits and vegetables daily. (See my books "What to Eat When" and "The What to Eat When Cookbook" for tips)

You'll stop killing the bacteria in your gut that makes you happy, strengthen your immune system, protect your brain, and keep yourself looking great.