This is the first in a series of five articles, each one expanding on a principle from Five Practices for a Life Aligned with Nature, where I laid out the five roots of my Purely Rooted philosophy. This article goes deeper on the first: Eat from the Earth.
Ninety-five percent of your body’s serotonin, the neurotransmitter most associated with mood, happiness, and emotional stability, is produced not in your brain but in your gut. Let that sit for a moment. The organ we associate with digestion is running the show on how we feel, and what we feed it determines how well it performs.
Eat whole foods. Avoid processed ones. Simple enough on the surface, but the science underneath is anything but simple, and it’s more convincing than I expected when I started digging into it.
The Gut-Brain Highway
Your gut and your brain are in constant two-way communication through what researchers call the gut-brain axis. The vagus nerve, the longest cranial nerve in the body, runs from the brainstem directly to the abdomen, carrying signals in both directions. Your gut bacteria produce neurotransmitters like serotonin, GABA, and dopamine. They manufacture short-chain fatty acids that reduce neuroinflammation. They influence your stress response, your sleep patterns, and even your food cravings.
A 2025 review published in PMC laid out the full picture: dietary choices significantly influence the gut microbiome, which in turn affects emotional, cognitive, and neurological health. High-fiber, plant-based diets increase microbial diversity, decrease inflammation, and strengthen communication along the gut-brain axis. Diets heavy in saturated fats and refined sugars do the opposite, promoting dysbiosis (microbial imbalance), increased inflammation, and greater risk of neuropsychiatric disorders.
In a 2024 randomized clinical trial, patients with major depressive disorder who received the probiotic Bifidobacterium breve CCFM1025 showed significant improvement in depressive symptoms. The probiotic altered tryptophan metabolism in the gut, which directly affected serotonin production. Depression improved not through a pharmaceutical antidepressant, but through feeding the right bacteria.
The Ultra-Processed Problem
If whole foods build a healthy gut, ultra-processed foods tear it apart. And “ultra-processed” doesn’t just mean junk food. It includes most packaged breads, breakfast cereals, flavored yogurts, protein bars, plant-based meat substitutes, and nearly everything sold in a drive-through window. These products are engineered in laboratories using emulsifiers, artificial flavors, and chemical preservatives that your gut bacteria have never encountered in evolutionary history.
The data is stark. A meta-analysis of observational studies found that for every 10% increase in ultra-processed food as a share of daily calories, the risk of depression rose by 11%. Adults with the highest UPF intake were 80% more likely to experience depressive symptoms compared to those with the lowest intake. And a 2024 umbrella review upgraded the evidence to “highly suggestive,” reporting an odds ratio of 1.40 for depression and 1.41 for common mental disorders among high UPF consumers.
The mechanisms are now well mapped. Ultra-processed foods cause rapid glucose spikes followed by crashes, creating metabolic instability. Their additives damage the intestinal lining, increasing permeability (what some researchers call “leaky gut”). Emulsifiers and artificial colorings disrupt the microbiome’s composition. And the resulting chronic low-grade inflammation doesn’t stay in the gut; it travels to the brain, interfering with serotonin and dopamine signaling.
What to Eat Instead
The prescription is not a new supplement or a branded diet plan. It’s food your great-grandmother would recognize. Leafy greens, root vegetables, legumes, whole grains, nuts, seeds, fermented foods like sauerkraut and kimchi. Foods that arrive without ingredient lists because they are the ingredient.
Fiber is the key nutrient most people miss. Your gut bacteria ferment dietary fiber into short-chain fatty acids like butyrate, which reduce inflammation and strengthen the gut barrier. Most Americans eat about 15 grams of fiber per day. The recommended minimum is 25-30 grams. Our ancestors likely consumed 100 grams or more. The gap between what our microbiome needs and what we actually give it is enormous.
Polyphenols, the compounds that give berries, dark chocolate, and green tea their deep colors, act as fuel for beneficial bacteria. Omega-3 fatty acids from flaxseed, walnuts, and hemp seed reduce neuroinflammation directly. Fermented foods introduce live bacteria that compete with harmful strains. None of this requires a degree in nutrition. It requires walking past the center aisles of the grocery store and spending your time around the edges, where the actual food lives.
Food as Foundation
I’ve come to see diet as the foundation for everything else in the Purely Rooted philosophy. You can spend time in nature, move your body, get morning sunlight, and ground yourself barefoot on the earth, but if your gut is inflamed and your microbiome is starving, those benefits are fighting uphill. Fix the gut first, and the rest amplifies.
The modern food system has made it extraordinarily convenient to eat in ways that make us sick, and extraordinarily inconvenient to eat in ways that keep us well. Processed food is cheap to produce, long-lasting on shelves, and engineered to trigger cravings. Whole food spoils faster, costs more per calorie, and doesn’t come with a marketing budget. But your gut doesn’t care about marketing. It cares about fiber, diversity, and the absence of chemicals it can’t process.
Start where you are. Swap one processed meal a day for a whole one. Add a handful of greens to whatever you’re already eating. Replace a packaged snack with a piece of fruit and some nuts. Your microbiome begins shifting within days, not months. And when your gut changes, your mood follows. It has to. They’re wired together.
Purely Rooted. 
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