Dietary Fs: Fiber and Fermented Foods for a Healthy Gut

An F may mean failure in school, but in your diet the two biggest Fs—fiber and fermented foods—earn top marks. They help maintain healthy digestion and may offer benefits for overall health. Here’s how to fit these nutrients into meals and support a thriving gut microbiome.

The Gut Microbiome

The gut microbiome is composed of bacteria, viruses, fungi, and other microorganisms in the colon. Diet, environment, and lifestyle shape its makeup. Sometimes called a “hidden organ,” the microbiome:

Supports the immune system
Reduces chronic inflammation
Keeps intestinal cells healthy
Provides certain micronutrients

Gut microbes also communicate with the brain via the gut-brain axis. Changes in the microbiome have been linked with mood and mental health disorders, though causality is not yet established. A healthy diet low in processed foods is key.

Benefits of Fiber

Fiber’s main job is to soften and add bulk to stool, promoting smooth digestion. It also:

Helps control body weight
Lowers LDL (“bad”) cholesterol
Reduces risk of heart disease, type 2 diabetes, and some cancers

There are two types of fiber:

Insoluble: adds fullness and encourages regular bowel movements
Soluble: helps lower cholesterol and blood sugar

Recent research suggests focusing on total daily fiber rather than type.

How to Increase Fiber Intake

Increase fiber gradually and drink plenty of water to avoid gas, bloating, or cramps. Your body adjusts over about a week. Use the formula:

14 g of fiber per 1,000 calories consumed.

Instead of tracking grams, add more servings of fiber-rich foods:

Fruits and vegetables
Legumes
Nuts and seeds
Whole grains

Over-the-counter fiber supplements (capsules, powders, tablets) can be used occasionally if you can’t meet needs through food, but they shouldn’t be your primary source.

The Role of Fermented Foods

Fermented foods deliver both prebiotics—ingredients that promote healthy microbiome changes—and live bacteria (probiotics). A healthy gut aids digestion, nutrient absorption, immune defense, and inflammation control. Some studies suggest probiotics may relieve symptoms of conditions like inflammatory bowel disease and irritable bowel syndrome, though evidence is mixed.

Most fermented foods undergo lacto-fermentation, where natural bacteria feed on sugars and starches, producing lactic acid and beneficial microbes like Lactobacillus and Bifidobacterium. Note that processes such as brewing beer or baking can remove or inactivate these microbes.

Yogurt (look for “live and active cultures” on the label)
Kimchi
Sauerkraut
Kombucha
Pickles

Fermented foods also provide enzymes, B vitamins, and omega-3 fatty acids. There’s no official recommended daily allowance for prebiotics or probiotics—just aim to include more fermented foods in your diet.

Probiotic supplements are available but aren’t FDA-regulated, so there’s no guarantee of strain or dosage. It’s best to get probiotics from fermented foods.

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