loamSoluble fiber
Soluble fiber dissolves in water to form a thick gel as it moves through your gut. That gel slows digestion, which helps steady blood sugar after meals and can help lower LDL ("bad") cholesterol. It's also the fiber your gut bacteria ferment most readily — food for your microbiome.
Good sources: oats, barley, beans, lentils, peas, apples, citrus fruit, carrots and psyllium.
Insoluble fiber
Insoluble fiber doesn't dissolve in water. Instead it adds bulk to stool and speeds transit through the gut — it's the regularity workhorse, helping food move through comfortably and on schedule.
Good sources: wheat bran, whole grains, nuts, seeds, and the skins of fruit and vegetables.
A quick comparison
| Property | Soluble | Insoluble |
|---|---|---|
| Dissolves in water | Yes | No |
| Main job | Feeds gut bacteria, slows digestion | Adds bulk, keeps you regular |
| Texture in gut | Gel | Roughage |
| Top sources | Oats, beans, apples, citrus, psyllium | Wheat bran, whole grains, nuts, veg skins |
Most whole plants contain both. Real foods aren't purely one type or the other — most whole plants contain both soluble and insoluble fiber in different ratios, so you rarely need to pick. There's also a special subset, prebiotic fiber, that most directly feeds beneficial microbes (more in our guide to prebiotic fiber). Eating a variety of plants covers all three naturally.
Do you need to balance them?
For most people, no active balancing is required. You don't have to count each type — eating a range of whole foods gives you a natural mix of soluble, insoluble and prebiotic fiber without any spreadsheet. But if you have a specific goal, it helps to know where to lean:
- After regularity? Lean into insoluble sources — whole grains, vegetables, wheat bran.
- After blood-sugar or cholesterol support, or feeding your microbiome? Lean into soluble and prebiotic sources — oats, legumes, psyllium.
See your soluble, insoluble & prebiotic split
Every food in loam's catalog is broken into soluble, insoluble and prebiotic fiber, and your Today screen shows all three as separate bars — so you can spot at a glance which type you're low on, instead of guessing from a single fiber total. Free, no account, private by design.
Download loam on the App Store →Frequently asked
Which is better, soluble or insoluble fiber?
Neither — they do different jobs. Soluble fiber slows digestion and feeds gut bacteria; insoluble fiber adds bulk and keeps you regular. Aim for both rather than picking one.
Is oatmeal soluble or insoluble fiber?
Mostly soluble — oats are rich in beta-glucan, a well-studied soluble fiber — but they also contain some insoluble fiber, like most whole plant foods.
What foods are high in soluble fiber?
Oats, barley, beans, lentils, apples, citrus fruit and psyllium husk are among the richest sources of soluble fiber.
Sources: standard nutrition references on fiber types and food sources, including U.S. Dietary Guidelines and Academy of Nutrition and Dietetics summaries. loam supports general wellness and education — it is not medical advice.