Feed Your Second Brain

How Your Gut Microbiome Shapes Your Cravings, Health, and Metabolism

Imagine carrying around an entire ecosystem inside your body.

Not a few hundred organisms.

Not a few thousand.

Trillions.

Hidden within your digestive tract lives an enormous community of bacteria, fungi, viruses, and other microorganisms collectively known as the gut microbiome. Scientists increasingly recognize the microbiome as one of the most important regulators of human health.

Current estimates suggest the average adult carries approximately 38 trillion microbial cells compared with about 30 trillion human cells. While these numbers vary from person to person, they remind us that we are not simply human—we are an intricate partnership between our own cells and trillions of microscopic companions.

The question is:

Who are you feeding every day?

That answer may determine far more about your health than you realize.

Your Gut Is Constantly Talking to Your Brain

For decades, scientists believed the brain controlled the gut.

Today we know the communication goes both directions.

This communication system is called the gut-brain axis.

Your gut and brain are connected through several pathways:

• The vagus nerve

• Hormones

• The immune system

• Chemical messengers produced by gut microbes

• Short-chain fatty acids created when bacteria digest fiber

Some researchers now refer to the gut as our “second brain.”

Although your gut does not think like your brain, it continually sends signals that influence:

• Hunger

• Fullness

• Mood

• Stress

• Energy

• Blood sugar regulation

• Inflammation

• Food cravings

This helps explain why changing the foods you eat often changes the foods you want.

Your Microbes Eat Before You Do

Every meal you consume also feeds trillions of microorganisms.

Different foods nourish different microbial communities.

Think of your microbiome like a garden.

Feed the flowers…

More flowers grow.

Feed the weeds…

More weeds appear.

The same principle applies inside your intestines.

Beneficial microbes thrive on:

• Vegetables

• Fruits

• Beans

• Lentils

• Whole grains

• Nuts

• Seeds

• Dietary fiber

These microbes produce compounds that:

• Reduce inflammation

• Strengthen the intestinal barrier

• Improve insulin sensitivity

• Help regulate appetite

• Support immune function

Less desirable microbial communities flourish with diets high in:

• Added sugars

• Highly processed foods

• Refined starches

• Diets consistently low in fiber

Over time, this dietary pattern can reduce microbial diversity and favor species associated with poorer metabolic health.

The remarkable part is that the microbiome is adaptable. As your eating pattern changes, the microbial community changes with it.

Why Your Cravings Begin to Change

Many people following the Unstacking Diet notice something surprising.

The cravings that once seemed impossible to resist slowly begin disappearing.

Why?

It’s not simply because you developed stronger willpower.

It’s because your biology is changing.

Beneficial bacteria produce compounds called short-chain fatty acids, especially butyrate, acetate, and propionate, when they ferment dietary fiber.

These compounds help:

• Improve blood sugar regulation

• Lower inflammation

• Support hormones involved in hunger and fullness

• Communicate with the brain through the gut-brain axis

At the same time, stabilizing blood glucose and reducing rapid insulin swings makes the brain less likely to signal for quick sources of energy.

The result?

Less mental “food noise.”

Many people describe feeling free for the first time in years.

What Is Leaky Gut?

Your intestines are designed to be selective.

They allow nutrients into your bloodstream while keeping bacteria, toxins, and partially digested food where they belong.

This protective barrier consists of:

• Intestinal cells

• Tight junction proteins

• A thick protective mucus layer

• Immune cells

• Beneficial bacteria

One important job of dietary fiber is feeding bacteria that help maintain this protective mucus layer.

When fiber intake remains chronically low, certain bacteria increasingly consume the mucus layer because it becomes one of the few remaining energy sources available to them.

Over time, this may thin the protective barrier.

Combined with inflammation and other factors, this can contribute to increased intestinal permeability, commonly called “leaky gut.”

Instead of acting as a tightly woven screen, the intestinal lining becomes more like a screen with enlarged openings.

Undesirable substances may cross into the bloodstream more easily, triggering immune activation and inflammation.

Why Does Leaky Gut Matter?

Research continues to evolve, but increased intestinal permeability has been associated with:

• Obesity

• Type 2 diabetes

• Metabolic syndrome

• Non-alcoholic fatty liver disease

• Inflammatory bowel disease

• Certain autoimmune diseases

• Cardiovascular disease

• Depression and anxiety

Scientists are still determining whether increased permeability is a cause, a consequence, or both in many of these conditions.

What is becoming increasingly clear is that maintaining a healthy intestinal barrier supports overall health.

Fiber: The Forgotten Superfood

When people think about nutrition, they often focus on protein.

Or carbohydrates.

Or fats.

Fiber rarely gets much attention.

Yet fiber may be one of the most powerful nutrients for improving metabolic health.

Unlike many carbohydrates, humans cannot digest fiber.

Instead…

Your microbes digest it.

Fiber becomes food for the beneficial bacteria living in your colon.

This process produces short-chain fatty acids that:

• Nourish the cells lining your colon

• Reduce inflammation

• Improve insulin sensitivity

• Strengthen the gut barrier

• Help regulate blood sugar

• Support immune health

• Increase feelings of fullness

In many ways, fiber feeds the tiny partners that help keep you healthy.

Most of Us Aren’t Getting Enough

The average American consumes only 15–17 grams of fiber per day.

Current recommendations are:

Women: approximately 25 grams per day

Men: approximately 38 grams per day

Many experts in gut health recommend aiming for 30 grams or more daily from a wide variety of plant foods to encourage a diverse microbiome.

Increasing fiber gradually while drinking adequate water can help reduce temporary bloating as your microbiome adapts.

Can Fiber Help During a Higher-Carbohydrate Meal?

One of my favorite practical strategies is using soluble fiber before meals.

Research has shown that consuming approximately 5–10 grams of soluble fiber, such as psyllium husk, shortly before or with a meal may:

• Slow stomach emptying

• Reduce blood sugar spikes

• Lower insulin responses

• Increase fullness

• Feed beneficial gut bacteria

The Unstacking Travel Tip

Carry single-serving packets containing approximately 7 grams of soluble fiber in your purse, briefcase, backpack, or car.

If you know you’re about to enjoy a higher-carbohydrate meal, mix one packet into a glass of water shortly before eating.

Think of it as adding another layer of protection for your metabolism.

This is not permission to regularly overeat processed foods.

Rather, it is a simple strategy that may help lessen the metabolic impact of an occasional higher-carbohydrate meal while simultaneously nourishing your microbiome.

The Unstacking Philosophy

Every meal does more than feed you.

It feeds trillions of organisms living inside you.

Every bite is a vote.

A vote for inflammation…

or healing.

A vote for cravings…

or freedom.

A vote for instability…

or metabolic health.

One of the greatest gifts of the Unstacking Diet is that it doesn’t simply change what you eat.

Over time, it changes the microscopic community that influences what you want to eat.

As beneficial microbes become more abundant, many people naturally begin craving fresh foods, vegetables, fruit, legumes, and other fiber-rich meals.

The battle with food becomes quieter.

Health no longer depends entirely on willpower.

Instead, your microbiome begins working with you rather than against you.

When you feed your second brain, your second brain starts taking care of you.

Key Takeaways

✓ Your gut contains approximately 38 trillion microbial cells, compared with about 30 trillion human cells.

✓ Your microbiome communicates constantly with your brain through the gut-brain axis.

✓ Diets rich in fiber support beneficial microbes that promote metabolic health.

✓ Diets high in ultra-processed foods and low in fiber can reduce microbial diversity and contribute to poorer metabolic health.

✓ Dietary fiber helps beneficial bacteria produce compounds that strengthen the intestinal barrier, improve insulin sensitivity, and reduce inflammation.

✓ Most adults consume far less fiber than recommended.

✓ Soluble fiber taken before meals may help reduce post-meal blood sugar spikes while supporting a healthier microbiome.

✓ Every meal feeds both you and the trillions of microbes that live within you.

Selected References (2021–2025)

• Fan Y, Pedersen O. Gut microbiota in human metabolic health and disease. Nature Reviews Gastroenterology & Hepatology. 2025.

• Nature Reviews Microbiology. The gut microbiome and metabolic disease. 2024–2025 review series.

• American Society for Nutrition. Dietary Fiber and Cardiometabolic Health. 2023.

• American Diabetes Association. Standards of Care in Diabetes. 2025.

• Sonnenburg ED, Sonnenburg JL. Research on dietary fiber, microbiome diversity, and intestinal mucus barrier.

• USDA Dietary Guidelines for Americans, 2020–2025 (current recommendations for fiber intake).

• Institute of Medicine/National Academies. Dietary Reference Intakes for Fiber.