The F-Word That Improves Metabolic Function Without Fail

By Kylie Buckner, RN

If there’s one “F-word” that can change your health from the inside out – it’s fiber.

Why? Because we’ve watched thousands of men and women between 35–65 lower their A1c, fasting glucose, cholesterol, blood pressure, and weight by doing one simple thing consistently: eating more fiber-rich whole foods.

In order to understand the ins-and-outs of why fiber is such a game changer, let’s walk through its metabolic magic step-by-step.

You Can’t Digest Fiber, But Your Bacteria Can

Fiber is technically a carbohydrate chain found only in plant foods, and your digestive system can’t metabolize it for energy for one simple reason.

Fiber is known as cellulose, and in order to cut cellulose into short chains, an enzyme called cellulase is required.

Here’s the problem – humans don’t make cellulase. We evolved with zero genes that encode for cellulase, which means that we don’t have the enzymatic machinery to cut cellulose at all.

Instead, the bacteria in the large intestine manufacture and secrete cellulase, which then cuts cellulose into glucose units. Then, those glucose units become fuel for the bacteria themselves.

In essence, the bacteria in the human microbiome secrete cellulase for selfish purposes – so that they can extract glucose and feed themselves.

What Does Fiber Do For YOU?

It’s easy to think that relying on bacteria to metabolize cellulose is a problem.

But guess what? It’s actually a feature, not a bug.

It’s actually a good thing that your digestive system doesn’t have the machinery to cut fiber into small pieces.

Fiber acts like a traffic cop in your digestive system, and that does a few things:

In your upper digestive tract, fiber:

• Slows the absorption of glucose into your blood, leading to a slower glucose rise in the post-prandial state

• Binds to cholesterol from your food, to prevent it from being absorbed into your blood

• Distends your stomach and small intestine, sending a signal to your brain to reduce your appetite

In your lower digestive tract, fiber:

• Feeds glucose to trillions of microbes in your gut microbiome

• Stimulates the production of anti-inflammatory short-chain fatty acids (SCFAs) that reduce oxidative stress in your colon, liver, pancreas, kidney, and brain

• Promotes the movement of material through your large intestine

The net effects are:

• Higher energy levels

• Lower post-meal blood glucose

• Significantly improved insulin sensitivity

• Reduced appetite (leading to weight loss)

• Bigger and more frequent poops (less constipation)

When people ask us for a single lever that moves nearly every health metric in the right direction – fiber is our #1 draft pick.

How Much Fiber Do You Need Every Day?

Most adults in the US eat less than 15 grams of fiber per day. That’s a problem.

Health authorities like the USDA and the Institute of Medicine recommend:

• 25 grams per day for women (ages 19–50)

• 38 grams per day for men (ages 19–50)

From having helped thousands of people to improved metabolic health, we’ve observed that when clients begin eating 50–75 grams of fiber per day, they see tremendous improvements in their blood glucose, cholesterol level, and blood pressure.

In addition, increasing fiber intake and keeping it consistently more than 75 grams per day is one of the most powerful weight loss strategies we’ve ever discovered.

And if that seems daunting, just know that inching up your fiber intake week by week is actually our preferred strategy because it prevents burnout and digestive discomfort.

Whole Food Fiber is Not The Same as Fiber Supplements

Your digestive system is designed to extract nutrients when they’re packaged in nature’s original container – whole fruits, vegetables, legumes, whole grains, and minimally processed soy products.

Products with “added fiber” or “prebiotics” try to add fiber powder often into processed foods .

They don’t deliver the same metabolic effects as eating beans, berries, greens, and intact grains.

Simple rule of thumb: if it sounds like a shortcut, it probably is.

Don’t Fear Fruits

Glucose in whole fruit is bound up with fiber and water, so it enters your bloodstream slowly and steadily.

Added sugars in beverages, candy, baked goods, and “healthy snacks” cause rapid glucose absorption, insulin spikes, and trigger inflammation.

If you’re living with prediabetes or type 2 diabetes, those rapid spikes are exactly what you want to avoid.

Choose fiber-bound carbohydrate-rich foods like mangoes, peaches, berries, or bananas over refined carbohydrate-rich foods.

Read Labels With No BS

If marketing says “organic,” “natural,” “made with whole grains,” or “high in fiber,” flip the package over.

The ingredient list and fiber grams per serving tell the truth.

Look for short ingredient lists, ingredients you recognize, and at least 5-10 grams of fiber per serving.

If sugar or one of its many nicknames shows up in the top three ingredients, put it back and walk away. Quickly.

A Simple Way to Build Fiber-First Meals

Use this mental template at every meal: start your plate or bowl with raw leafy greens, add legumes, then surround with colorful vegetables, add a whole grain, include a piece of fruit, and add a small amount of nuts or seeds.

When you lead with fiber, protein and whole carbohydrate-rich foods take care of themselves.

• Breakfast could be steel-cut oats topped with blueberries, ground flax, and cinnamon, plus a side of sliced mango

• Lunch might be a big chopped salad with mixed greens, red beans, quinoa, cherry tomatoes, cucumbers, and a lemon–tahini dressing

• Dinner could be tofu and veggie stir-fry over brown rice with edamame on the side

• Snacks that love your metabolism include an apple with a handful of walnuts or carrots with hummus

Our Favorite Fiber-First Foods

• Red beans are a star for taste, texture, iron, and a great macro profile. Lentils, black beans, chickpeas, and split peas are equally powerful.

• Quinoa, steel-cut oats, barley, farro, and brown rice deliver steady energy. Berries, pears, apples, bananas, and mangoes are fiber-forward fruits.

• Leafy greens, broccoli, corn, brussels sprouts, cauliflower, peppers, onions, and mushrooms add volume, micronutrients, and serious gut benefits.

• Tofu, tempeh, and potatoes round out meals with satisfying texture and staying power.

How to Ramp Up Without the Bloat

If your current fiber intake is low, increase your fiber intake gradually and hydrate well to avoid digestive discomfort, bloating, and pain.

Add ONE fiber-rich food per meal, chew thoroughly, and give your microbiome a week or two to adjust before adding a second.

If you use medications that affect digestion or blood sugar, keep your healthcare provider in the loop as you increase whole plant foods.

Also, log your food in a food logging app like Cronometer or My Fitness Pal. These are amazing tools that help you quantify and take the guesswork out of meal planning.

The Bottom Line About Fiber

Fiber is the metabolic multiplier.

Prioritize it at every meal and watch your fasting glucose, A1c, cholesterol, blood pressure, and waistline trend in the right direction, without white-knuckle dieting.

Skip the gimmicks and added-fiber products.

Eat real plants in their natural package and let the compounding benefits do their thing.