Types of Fiber

Wheat dextrin is a soluble fiber made from treated wheat starch and the main ingredient in Benefiber. It dissolves clear and feeds gut bacteria, but it doesn’t gel, so it does little for constipation or cholesterol; in one trial, extra gas appeared only from 30 g a day.

Psyllium husk is the seed coat of the Plantago ovata plant, a soluble fiber that swells into a gel and is the active ingredient in Metamucil. Across 28 trials, about 10 g a day lowered LDL cholesterol by roughly 13 mg/dL.

Polydextrose is a low calorie soluble fiber made from glucose, supplying about 1 calorie per gram compared with 4 for sugar. About 60% of it passes out unfermented, and the average laxative threshold sits near 50 g in a single dose.

PHGG, or partially hydrolyzed guar gum, is a gentle prebiotic fiber that dissolves clear and causes less gas than most fiber powders. In a 12-week IBS trial, 6 g a day cut bloating scores by 4.1 points, versus 1.2 with placebo.

Oat fiber is ground oat hull, about 85% fiber and almost entirely insoluble, with roughly 24 calories per 100 g. That makes it a handy low-carb baking ingredient, but it isn’t oat bran: hull fiber carries almost no beta-glucan and doesn’t qualify for the FDA’s oat heart claim.

Methylcellulose is a modified plant fiber, best known as Citrucel, that gut bacteria don’t ferment, so it softens stool with very little gas. A 1988 trial found it increased stool frequency in people with constipation at doses as low as 1 g a day.

Inulin is a soluble prebiotic fiber, mostly extracted from chicory root, that feeds bifidobacteria in the colon. In a 2010 trial, 10 g of native inulin at breakfast was well tolerated, while the same dose of shorter-chain oligofructose caused substantially more gas and bloating.

Guar gum is a soluble fiber from guar beans, used in tiny amounts to thicken foods like ice cream and sauces. At 5 to 10 g in a meal, trials cut the peak blood sugar rise by 41 to 68%, but dry guar diet pills caused 17 reported throat blockages by 1990.

Ground flaxseed gives you two fibers at once: about one third soluble, gel-forming mucilage and two thirds insoluble fiber from the seed coat. In a 2012 trial, flax fiber in a drink cut LDL cholesterol by 15%, while the same fiber baked into bread cut it by 9%.

Glucomannan is a highly viscous soluble fiber from konjac root that swells into a thick gel in water. Pooled trials show it lowers LDL cholesterol by about 10%, but for weight loss the average edge over placebo was just 0.22 kg.