Dietary fiber

Dietary fiber (also fiber): Dietary fiber is a category of carbohydrate that human digestive enzymes can't break down. It comes in two main types: soluble (which slows digestion and feeds gut bacteria) and insoluble (which adds bulk to stool).

Daily targets

The U.S. Dietary Guidelines recommend 25–34g of fiber per day for adults, depending on age and sex. The average American eats about 15g — well below the target.

Sources

Best sources include beans and lentils (15g per cup cooked), chia seeds (10g per ounce), berries (8g per cup raspberries), oats (4g per cup cooked), and most vegetables. Fiber supplements (psyllium husk) are an option but whole foods are preferred.

Why it gets subtracted from net carbs

Because fiber doesn't raise blood glucose meaningfully, low-carb and keto plans subtract it from total carbs to get the "net carbs" number. The U.S. FDA doesn't officially recognize this calculation but it's standard practice.