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For most people, the word “fiber” conjures images of thread and yarn; it seems out of place as a term for describing components of food. Nutrition scientists used to call it roughage (“scours your colon like a scrub brush.” Ouch!), or bulk (because it makes digestive waste softer, bulkier, and easier to eliminate). 
 
It’s easy to think of whole grains, bran, nuts, raw salad greens, and potato skins as roughage, yet many high-fiber foods aren’t rough or stringy at all, but thick and gelatinous, or smooth and creamy—think applesauce, oatmeal, avocado, mashed pumpkin.

So just what is dietary fiber, anyway?

In the diet, fiber means any carbohydrate molecule that resists digestion in the small intestine. 

Researchers have identified two main classes of dietary fiber in the diet: soluble and insoluble. (Most plant foods contain a mixture of soluble and insoluble fibers, which is why you’ll often see a food or class of plant foods appearing in both lists.)

• Soluble fibers dissolve in water to create gels that can be fermented by bacteria in the large intestine, serving as “prebiotics,” that promote the growth of beneficial gut bacteria. Foods rich in soluble fiber include dry beans and lentils, barley, oats (especially oat bran) and oatmeal, avocados, apples and applesauce, pears, carrots, citrus fruits, blueberries, strawberries, peas, potatoes. Soluble fibers help slow digestion, enabling the small intestine to absorb more nutrients. 
• Insoluble fibers don’t dissolve, but absorb water, adding bulk to digestive waste, thus helping to speed its passage out of the body. Foods high in insoluble fiber include 100 percent whole-wheat products, wheat bran, artichokes, blackberries, cooked dry beans and lentils, nuts, cauliflower, skins of apples, potatoes, green beans, and peas.
• A third category, resistant starches, are starch molecules that aren’t digested and that act like soluble fibers in the gut, providing “food” for useful gut bacteria, which in turn reduce inflammation and the risk of colon cancer, reduce spikes in sugar, and help you feel fuller faster. Resistant starches are abundant in beans (especially white beans), lentils, potatoes, and white rice. Cooking legumes and potatoes and then completely cooling them greatly increases the resistant starch content. Reheating won’t lower it again.

Why do we need fiber? 

Analyses of hundreds of studies have shown that eating a high-fiber diet reduces the risk of cardiovascular, bowel, and respiratory diseases, diabetes, and some cancers, lowers cholesterol, reduces fat absorption, helps prevent weight gain, enhances mineral absorption, lessens spikes in blood sugar, and improves immune response.

5 easy ways to get fiber in your diet

Current research suggests adults should consume at least 25 to 30 grams or more per day of dietary fiber—for most people, the more the better.

Increase the fiber content of your meals and snacks gradually to give your digestive system time to adapt.

1. Experts encourage you to get your fiber from whole foods, rather than fiber supplements. Whole foods provide a broad diversity of other nutrients and health-promoting along with the fibers.
2. Eat whole fruits and vegetables, both raw and cooked, rather than juices; eat the skins of fruits and vegetables whenever possible.
3. Drink plenty of water (or get it in soups, stews, and fruit) as you increase your fiber intake; the insoluble fibers need to absorb it to do their job.
4. Start by learning the of common foods. Read labels and make higher-fiber choices in processed and snack foods. Then, stop worrying about it, and simply plan to eat a wide variety of whole plant foods every day. 
5. The best rule of thumb for increasing the fiber in your diet: eat more plant foods, especially beans and lentils, the superstars of the high-fiber firmament. Eat more and a greater variety of vegetables and fruits, more whole grains, more seeds, and more nuts.

 It’s really not all that rough a job!

 See our chart on best source of fiber.