Fiber is the part of plant food your enzymes cannot digest. It slows glucose absorption, feeds gut bacteria, and adds bulk that keeps digestion moving. Because it passes through without being absorbed, foods high in fiber typically deliver fewer usable calories than their carbohydrate count suggests.
How much you need
Most health authorities recommend 25–30 g per day for adults, though average intake in Western diets lands near 15 g. Soluble fiber (oats, beans, apples) helps with cholesterol and blood sugar; insoluble fiber (bran, whole grains, vegetable skins) mainly helps with transit and regularity.
Where the database's leaders live
On this site's fiber ranking, legumes, bran cereals, and certain seeds dominate — values above 10 g per 100 g are common there. Whole fruits and vegetables cluster in the 2–6 g band, still useful because they are eaten in larger portions and carry water with them.
Increasing intake without discomfort
Jumping from 15 g to 35 g overnight usually causes bloating. Raise intake gradually over two to three weeks and add water along the way, since soluble fiber needs fluid to do its job. Beans and lentils cause less trouble when introduced slowly or soaked and cooked thoroughly.
Fiber and sugar
Compare the fiber figure next to sugars on any fruit entry: an apple's sugar arrives packaged with fiber and water, while apple juice's does not. That single difference is why whole fruit and juice should not be treated as equivalents.