What Is Dietary Fiber and How Much Do You Need?

Dietary fiber is the part of plant foods that your body can’t fully digest or absorb. Instead of being broken down like sugar or starch, it travels through your digestive system, where it adds bulk, keeps things moving and feeds the helpful bacteria in your gut. US guidelines suggest about 14 grams of fiber for every 1,000 calories you eat, and most Americans get less than that.

The two main types of fiber

Most plant foods contain a mix of both kinds:

• Soluble fiber dissolves in water and forms a gel. It slows digestion, which can help you feel full and may soften blood sugar rises after meals. Some types, such as the beta-glucan in oats and barley, can help lower LDL (“bad”) cholesterol. You’ll find soluble fiber in oats, barley, beans, lentils, apples, citrus fruit and psyllium.
• Insoluble fiber doesn’t dissolve. It adds bulk to stool and helps food pass through your intestines, which supports regularity. Good sources include wheat bran, whole wheat, brown rice, nuts, and the skins of fruits and vegetables.

There’s no need to track the two separately. Eating a variety of plant foods gives you both.

How much fiber do you need?

The Dietary Guidelines for Americans, 2020-2025, base fiber targets on about 14 grams per 1,000 calories. In practice, that’s roughly 22 to 34 grams a day for adults depending on age and sex, with younger men at the higher end. On Nutrition Facts labels, the Daily Value for fiber is 28 grams.

Because most people fall well short, the guidelines list fiber as a dietary component of public health concern. The encouraging part is that a few small swaps add up fast.

High-fiber foods to know

Values are approximate and can vary by variety and preparation.

What 30 grams can look like

Here’s one way to reach a little over 30 grams with ordinary groceries:

• Breakfast: oatmeal made with 1/2 cup rolled oats, topped with 1/2 cup raspberries and a tablespoon of chia seeds (about 12 g)
• Lunch: a burrito bowl with 1/2 cup black beans, a cup of brown rice, salsa and lettuce (about 11 g)
• Snack: a medium apple (about 4.5 g)
• Dinner: fish or tofu with a cup of broccoli and a small side salad (about 6 g)

How to add fiber comfortably

Going from very little fiber to a lot overnight can bring gas, bloating or cramps. A gentler path:

1. Add one higher-fiber food every few days rather than overhauling everything at once.
2. Drink enough fluids, since fiber works best with water.
3. Spread fiber across meals instead of loading it into one.
4. Swap rather than pile on: brown rice for white some nights, half whole-wheat pasta in the pot, or beans in place of some of the meat in a stew.
5. Leave the skins on potatoes, apples and pears when you can.

If you live with a digestive condition such as irritable bowel syndrome or inflammatory bowel disease, certain high-fiber foods may trigger symptoms. A doctor or registered dietitian can help you find the types and amounts that suit you.

Fiber and your gut

Some fibers become food for the bacteria in your large intestine. As those microbes ferment fiber, they produce short-chain fatty acids, compounds that help nourish the cells lining your colon. This is where fiber overlaps with prebiotics, which we cover in prebiotics vs probiotics. Fiber is also the reason food packages sometimes show a gap between total and “net” carbs, explained in net carbs vs total carbs.

The bottom line

Fiber is the indigestible part of plant foods, and it supports digestion, fullness, heart health and a well-fed gut. Aim for roughly 14 grams per 1,000 calories, which for most adults lands somewhere between the low 20s and mid 30s each day. Beans, lentils, whole grains, fruit, vegetables, nuts and seeds will get you there, especially if you build up gradually. Our guide to complex carbs has more ways to work whole grains into your week.