Ask a room of executives which nutrient they are most deficient in and you will hear vitamin D, magnesium, maybe protein. Almost nobody says fiber. Yet roughly 95 percent of adults fail to hit the recommended intake, and the average professional eats somewhere between 12 and 16 grams a day — about half of what the research associates with lower mortality, better blood sugar, healthier cholesterol, and a more resilient gut. Fiber is not glamorous. It does not come in a sleek bottle. It is also one of the highest-return changes most of my clients ever make.
I'm Dr. Jason Rannfeldt, a health performance coach who works with founders, executives, and high performers on building energy and longevity systems that survive real calendars. In this article I'll explain what fiber actually does, the difference between the types, how much you need, and the exact protocol I use to double a client's intake without wrecking their digestion. If you want broader context on how I approach food, start with Nutrition Fundamentals That Actually Work.
What fiber actually is
Fiber is the part of plant foods your own enzymes cannot digest. That sounds like a flaw; it is the entire point. Because it passes through the small intestine largely intact, fiber changes how quickly everything else is absorbed, binds compounds you would rather excrete, and arrives in the colon as food for the trillions of bacteria that make up your microbiome. Those bacteria ferment it into short-chain fatty acids such as butyrate, which fuel the cells lining your gut, tighten the intestinal barrier, and send anti-inflammatory signals throughout the body. I covered the bacterial side in depth in Gut Health and Performance and The Gut-Brain Connection.
Soluble vs. insoluble: why the type matters
Soluble fiber dissolves in water and forms a gel. Oats, barley, beans, lentils, chia, flax, apples, citrus, and psyllium are rich sources. This gel slows gastric emptying, blunts glucose spikes, and traps bile acids so your liver pulls more cholesterol out of circulation to make new ones. That is the mechanism behind fiber's well-documented LDL and ApoB lowering effect.
Insoluble fiber does not dissolve. Found in whole grains, nuts, seeds, vegetable skins, and leafy greens, it adds bulk and keeps things moving. It is the regularity fiber.
A third category matters too: fermentable and resistant starch — cooled potatoes and rice, green bananas, legumes — which feeds butyrate-producing bacteria particularly well. You do not need to track these separately. You need variety, which is why I push clients toward thirty different plants a week rather than one heroic bowl of bran.
Fiber and blood sugar
For an executive, the most immediately noticeable benefit is steadier energy. A meal with 10 grams of fiber produces a meaningfully smaller and slower glucose curve than the same calories without it. Smaller spikes mean smaller crashes, which means fewer 3pm cravings and less reliance on caffeine. If you have read The Afternoon Energy Crash or Blood Sugar and Executive Focus, fiber is one of the cheapest levers in both protocols. Over months, higher fiber intake is consistently associated with improved insulin sensitivity — a core pillar of metabolic health and metabolic flexibility.
Fiber and your heart numbers
Soluble fiber is one of the few dietary changes with reliable, dose-dependent effects on LDL cholesterol. Roughly 5 to 10 grams of soluble fiber per day lowers LDL by about 5 to 10 percent in most trials, and psyllium in particular has strong data. That is not a substitute for medication when medication is warranted, but it is a meaningful, side-effect-free contribution. If you have not yet tested your ApoB, read ApoB: The Cholesterol Number Every Executive Should Know and pair it with the broader cardiovascular framework in Blood Pressure and Cardiovascular Health.
Fiber, appetite, and body composition
Fiber increases meal volume without adding many calories, slows digestion, and stimulates satiety hormones like GLP-1 and PYY. Clients who raise fiber alongside protein almost always report eating less without trying. That combination — high protein, high fiber — is the backbone of how I help clients reduce visceral fat while protecting muscle, as described in Protein and Muscle for Longevity.
Fiber and inflammation
The short-chain fatty acids produced when bacteria ferment fiber dampen systemic inflammation and support immune regulation. Low-fiber, ultra-processed diets starve those bacteria and thin the protective mucus layer of the gut. This is part of why I treat fiber as foundational in Inflammation and Modern Performance and in Immune Resilience for Executives.
How much you actually need
The standard target is about 14 grams per 1,000 calories — roughly 25 grams for most women and 30 to 38 grams for most men. Large meta-analyses suggest benefits continue up to around 40 grams. My practical target for most executive clients is 30 to 40 grams per day, from at least 20 to 30 different plants per week.
The protocol I use with clients
1. Measure for three days. Most people dramatically overestimate their intake. Log honestly and find your baseline.
2. Increase by 5 grams per week. Going from 15 to 35 grams overnight is how people end up bloated and quitting. The microbiome needs time to adapt.
3. Anchor every meal. Breakfast: oats, chia, berries, or ground flax. Lunch: a legume or a large vegetable base. Dinner: two vegetables and a fiber-rich starch. The list in The Gut-Friendly Foods I Tell Every Client to Add is a good starting menu.
4. Use psyllium as insurance. One teaspoon to one tablespoon of psyllium husk in water adds 4 to 7 grams of mostly soluble fiber. Take it away from medications and other supplements by at least two hours.
5. Drink more water. Fiber without fluid causes the very constipation it is supposed to prevent. Pair this with the guidance in Hydration and Electrolytes.
6. Eat fiber first. Starting a meal with vegetables or salad before starches measurably blunts the glucose response. It is a small sequencing change with outsized returns.
Who should be careful
People with IBS, SIBO, inflammatory bowel disease in a flare, or recent bowel surgery may need a slower, more targeted approach, sometimes temporarily lower in fermentable fibers. Anyone with persistent digestive symptoms should involve their physician. Fiber is powerful precisely because it changes the gut — which means it should be introduced thoughtfully, not recklessly.
Why executives miss it
Busy schedules default to convenience food, and convenience food is almost always stripped of fiber. Travel days, client dinners, and protein-bar lunches add up. The fix is not willpower; it is building defaults — a stocked desk drawer, a standing breakfast, a repeatable lunch order. That is the core argument in Why Willpower Is the Wrong Tool for Behavior Change, and it applies here perfectly.
For more on my philosophy of building sustainable health systems, visit Jason Lee Rannfeldt.
The bottom line
Fiber is the rare nutrient that improves blood sugar, cholesterol, appetite, inflammation, and gut health at the same time — and it costs almost nothing. Measure your baseline, climb 5 grams a week, aim for 30 to 40 grams from a wide variety of plants, and drink the water to match. If you want your nutrition, training, sleep, and biomarkers sequenced into one coached system, that is the work inside Crush 90 and Thrive 90. Start with a conversation on the contact page, or learn more about the approach on the about page.
Ready to rebuild your health?
If this resonates, the next step is a conversation. Dr. Jason Rannfeldt works one-on-one with clients ready to commit to long-term transformation.