The Right FiberS to Optimize GLP-1 and Weight Health

The conversation about GLP-1 medications has done something useful: it has made weight-health hormones a household topic. People who had never heard of GLP-1 two years ago now know it (or at least its medication form) as a key player for satiety, appetite, blood sugar, body fat and aspects of metabolic function. That is genuinely good.

What the conversation has not done is explain what it and its colleagues, all of your weight-health hormones, actually need from your daily nutrition to function optimally — with or without a medication.

The answer is not more fiber.

The answer is more diverse fiberS, distributed consistently across your day, matched to your individual gut ecosystem. Recommendations have focused on amount alone. Have differentiated needs based on sex and age. And that’s not better.

Among those needs and wins? When you fiberS better, your body’s team of weight-health hormones gets what it needs when it needs it where it needs it. And that’s what we are here to gain further insight on today.

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Weight health is not a number on a scale. Total weight has long been a standard measurement, often compared to your height as body mass index (BMI). And it has done the opposite of giving us any helpful data about your body’s health and operational status.

Weight health is the assessment of your body’s weight’s composition - bone, muscle, fat and water — where their types, amounts, and location provide key signals about your body’s operational status. If they are each what they should be, then it is operating as intended and desired. It is weight healthy. And if any are not, then it is not. And we decode the signals to see what is suboptimal, and why.

Your weight composition, not a total number, one of the more reliable signals of your health today and your trajectory tomorrow.

When weight health is optimal, bone is dense because building and breakdown are balanced, muscle, too, is similarly building, repairing and being maintained, fat is distributed appropriately to support organs, protect bone and brain health, rather than concentrating viscerally where it is negatively impacting your inflammatory response and metabolic health, and fluid is balanced inside and outside your cells, helping to move nutrients and waste, being absorbed and moving waste through for successful elimination.

When weight health is suboptimal, the reverse is true in combinations that vary.

Your weight-health hormones are a set that helps govern activity impacting all four of these components. They include ones we know well and are just getting to know GLP-1, GIP, CCK, PYY, and amylin.

When this hormonal system is functioning optimally, weight health tends to follow. When their function is suboptimal, a person will struggle with one or more aspects of weight health regardless of diet and exercise.

Let’s now explore how fiberS act as central to your weight-health hormonal system.

Here are the weight-health hormone-by-hormone fiber relationship insights.

Glucagon-like peptide-1 lives in the L-cells in your gut lining from the small intestine through the large intestines, your colon. Its jobs include telling other hormones and actions to occur affecting appetite, digestive pace, insulin activity, vascular tissue activity and likely more.

The medications that have transformed the weight health conversation work by activating GLP-1 receptors pharmacologically. This means your body doesn’t have to receive signals to stimulate their activity, or have the resources to make them, nor does it need to wait for GLP-1 to reach receptors for it to cause other actions to occur.

But a body without the medication or one that is looking to come off the medication, it needs all of the above to occur. Your digestive tract is designed to produce GLP-1. FiberS are a primary dietary driver of that production.

Two fiber types activate GLP-1 through distinct pathways, and both matter.

Viscous gel-forming fiber stimulates GLP-1 release directly from L-cells in the small intestine. When viscous fiber contacts water in the digestive tract it forms a thick gel that slows the movement of nutrients through the gut, extends contact time between nutrients and L-cells, and triggers GLP-1 secretion as part of the satiety signaling cascade. The foods with the strongest viscous fiber profiles are chia seeds, basil seeds, flax seeds, psyllium, kiwi, and oats via beta-glucan. These are not interchangeable with fiber supplements or high-fiber packaged foods that contain other forms of fiberS. The physical property of viscosity is what drives the L-cell response, and that property is specific to these fiber types.

Fermentable prebiotic fiber activates GLP-1 through a second and complementary pathway. When fermentable fiber reaches the colon it is metabolized by gut bacteria into short-chain fatty acids, primarily butyrate, propionate, and acetate. Butyrate and propionate act directly on receptors on L-cells called FFAR2 and FFAR3, triggering GLP-1 secretion in the colon. This is a downstream, ecosystem-dependent pathway. It requires a diverse and healthy gut microbiome capable of fermenting fiber efficiently. The best food sources of these fiberS are garlic, onions, leeks, asparagus, artichokes, underripe bananas, chicory, uncooked oats, and the lignans in flax seeds.

The critical insight here is that a person eating only one type of fiber is activating only one of these pathways, or neither of them well. Someone eating insoluble fiber from wheat bran and nothing else is not producing optimal GLP-1. Someone taking a single fiber supplement without attention to type or timing is likely missing both pathways entirely. GLP-1 optimization through fiber requires both viscous and fermentable types, consistently present across the day. That’s what we assess and optimize with your personalized fiber plan.

Glucose-dependent insulinotropic polypeptide is secreted from K-cells located primarily in the upper small intestine in response to nutrients, particularly carbohydrates and fats. It amplifies insulin secretion in response to glucose, making it a key player in blood sugar regulation after consuming calories. And critically for weight health, GIP receptors are present on osteoblasts, the cells that build bone. GIP is one of the primary hormonal links between nutrition and bone formation. This is among the top reason I focus so much on gut-bone health, and also decry the oversimplified conversations about GLP-1 medications and bone health.

The fiber-GIP relationship is less direct than the fiber-GLP-1 relationship. From GLP-1 we learned that viscous fibers slow gastric emptying. It will impact the pace and form in which nutrients reach K-cells in the small intestine. A slower, more gradual nutrient delivery gives K-cells a more sustained stimulus rather than a rapid surge followed by a sharp drop. This modulated nutrient delivery pattern is associated with a more favorable GIP response and better insulin response after caloric intake.

For weight health, the GIP-bone connection is particularly significant. In the context of a diet chronically low in diverse fiberS, gastric emptying is faster, nutrient delivery to K-cells is less regulated, and GIP’s downstream signaling to osteoblasts is less supported. A comprehensive bone health strategy that omits fiberS optimization is missing a very important part.

Cholecystokinin is secreted from I-cells in the small intestine — yeah you have a whole alphabet at play in your football fields long digestive tract (!!) — in response to fat and protein in the gut. Its jobs include sending signals back to the brain to communicate a fullness message, it also impacts gastric emptying pace (slows it), and it stimulates the release of digestive enzymes from the pancreas and bile from the gallbladder. These substances allow for food to be broken down into usable nutrients before being moved along for delivery to their destinations.

Fiber activates CCK like GIP: by slowing gastric emptying and extending the contact time between nutrients and I-cells. Viscous fiber is the most effective fiber type too. The longer nutrients remain in contact with I-cells, the more sustained the CCK signal, and the more effectively fullness is communicated to the brain. This is one of your best tools to prevent overconsumption.

This is where the “eat fiber at the start of a meal” recommendation comes from. It’s valuable advice because eating fiber at the beginning of a meal rather than not having at all or waiting to the end can produce a meaningfully different satiety outcome. Where it can lose value is when your appetite is already low or non-existent, or when one consumes a poor-quality or the wrong types of fiberS to start their meal.

Have you found changing your fiber timing or types has affected your meal or snack intake - what or how much you consume? Do you have questions about which fiberS are better?

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Peptide YY gets released along with GLP-1 from L-cells, which means it shares some of the same fiber-driven stimuli. PYY suppresses appetite and slows intestinal transit, primarily providing satiety reinforcement in the hours after a meal rather than during it. Where GLP-1 and CCK signal fullness during eating, PYY extends the duration of that signal between pit stops (meals or snacks).

Fermentation is the primary driver of PYY activation from fiberS. Fermentable fibers that feed gut bacteria and produce SCFAs are the most effective at sustaining PYY levels between meals.

People who eat adequate total fiber but feel hungry again too quickly between meals are often getting the wrong types. The fermentable component that sustains PYY is frequently what is missing.

Amylin is going to get a lot of attention in 2027. Be prepared for her to be as “IT” as GLP-1 and then some, especially on the medication front. Unlike the others, it is not a gut hormone but rather o-secreted with insulin from pancreas, its beta-cells, in response to food intake. Like GLP-1 and CCK, it slows gastric emptying and promotes satiety when it reaches the brain receptors and tells other hormones to go to work, contributing to the coordinated hormonal response that follows a pit stop. It also plays a role in blood sugar regulation.

The fiber connection to amylin is indirect but worth mentioning as it introduces more diversity requirements. Resistant starch, a functional fiber subtype that resists digestion in the small intestine and ferments in the colon, has been shown to improve insulin secretion. Because amylin is co-secreted with insulin, dietary strategies that improve insulin secretion would then support amylin release at the same time. You do not activate amylin directly through fiber the way viscous fiber activates L-cells. You support the conditions in which amylin is more likely to be secreted optimally.

Resistant starch is technically a starch, not a classic fiber, but it functions like one and its contribution to the insulin and amylin response is a meaningful part of the weight-health hormone picture. Resistant starch sources include cooked-and-cooled rice, oats and potatoes, green bananas, legumes, and unmodified potato starch. CARBS?! These are not what most people associate with weight health optimization. They are also not foods that appear on standard fiber charts. And that’s a problem. It is one of the main problems with recommendations that exclusively counting total fiber grams or two types of fibers rather than true diversity and timing.

Your weight-health hormones have different fiber type affinity, different anatomical locations for secretion, and different timing profiles for activation. GLP-1 and PYY require both viscous fiber in the small intestine and fermentable fiber in the colon. CCK needs viscous fiber early in the meal. GIP needs regulated nutrient delivery paced by viscous fiber. Amylin needs the insulin-supporting conditions that resistant starch helps create.

Learning this we can see where fiber intake plans focusing on an amount of grams typically fail. Instead, it is a compelling arguments for fiber diversity: a diet that includes viscous fiber for in-meal satiety via GLP-1 and CCK but lacks fermentable fiber will leave PYY under-activated, resulting in hunger returning faster between pit stops regardless of how much fiber was consumed.

No single fiber type serves all of these functions. No daily gram total, however high, captures whether you are feeding the right types at the right times in the right distribution across your day.

A diet high in wheat bran and low in fermentable fiber will support transit but underserve GLP-1, PYY, and amylin. A diet high in psyllium but low in fermentable fiber will activate viscous pathways but miss the SCFA-driven colonic GLP-1 and PYY activation. A diet high in total fiber from processed high-fiber foods will hit a gram count while delivering fiber types that the gut ecosystem cannot ferment effectively and that lack the physical properties needed to stimulate L-cells and I-cells optimally.

This is why the Fiber Optimization Playbook is built around type, amount per pit stop, and timing rather than a daily total. The daily total is the output of getting these three things right. It is not the input.

Whether you are on a GLP-1 medication, reducing your dose, or never started one, this framework applies.

If you are on a GLP-1 or dual GLP-1/GIP medication, you are activating these receptor pathways pharmacologically. FiberS optimization ensures that your nutritional inputs support rather than compete with that pharmacological effect. It reduces digestive side effects by providing the right fiber types at the right times for a gut with already-slowed motility. It supports nutrient absorption rather than undermining it. And it builds the nutritional foundation that the medication is designed to augment.

FiberS optimization on a GLP-1 medication is one of the key strategies to optimize results while on the medication and in the event that you choose to or have to reduce or eliminate it as a weight-health hormone source.

If you are reducing your dose or transitioning off a medication, fiberS optimization is one of the primary nutritional strategies to transition from the sustained impact of exogenous (medication) hormone sources to endogenous (your own body’s).

If you are not on and have never been on a GLP-1 medication, your body’s weight-health hormone system is running on the nutritional inputs you give it every day. FiberS are among the most evidence-supported dietary levers for optimizing that system. Not the only lever, but an absolutely foundational one.

The goal is not to overhaul your eating immediately. It is to audit your current fiberS intake against the diversity your weight-health hormone system actually requires.

At each pit stop, aim for 5 to 7 grams of fiber from more than one type. Include at least one viscous source (chia seeds, basil seeds, flax seeds, kiwi, oats) and at least one fermentable source (garlic, onion, leeks, asparagus, underripe banana, uncooked oats) consistently across your day. Add resistant starch sources to your routine several times a week to support the insulin and amylin side of the picture.

At The Better Nutrition Program, I have trained a team to personalize fiberS optimization plans, it is that training that I have provided to readers who may want to DIY it via my bestselling book Your Best Shot.

If this brought up more questions, considerations, frustrations or concerns and you want to understand how your motility, your medications, your activity, and your sleep are also shaping what your ecosystem specifically needs, that is the conversation our team is here to have.

Book a free consult here

Better not perfect. This month, we are optimizing the foundation.

Ashley Koff, RD is a registered dietitian with 25 years of clinical experience, founder of The Better Nutrition Program, and author of Your Best Shot: The Personalized System for Optimal Weight Health — GLP-1 Shot or Not. She is Nutrition Course Director at UCI’s Integrative and Functional Medicine Fellowship.