Fiber is part of the carbohydrate group and is found, to one degree or another, in all grains, fruits, vegetables, pulses, legumes and nuts. Technically a non-starch polysaccharide (NSP for short), our digestive systems lack the necessary enzymes to break fiber down and so, as far as we are concerned, fiber is a calorie-free food.
Although fiber does not contribute any energy to your daily diet, it provides numerous other health-related benefits.
Types of Fiber
Fiber is dived into two types, based on how each interacts with water.1
- Soluble fiber. This type of fiber dissolves in water and forms a gel-like substance as it passes through the digestive track, which slows digestion. Like a dry sponge, it soaks up liquid as it passes though your intestines and absorbs small but significant amounts of bile acid, cholesterol, fats and harmful toxins in your digestive system. Think of soluble fiber as your friendly digestive-tract cleaner!
Soluble fiber is found in most root vegetables, the soft flesh of fruits, legumes, peas, and beans. E.g. oats, barley, beans, lentils, peas, psyllium, citrus fruits, berries and apples. - Insoluble fiber. This type of fiber does not dissolve in water and passes through the digestive system whole. Insoluble fiber is sometimes called roughage, and just like an old-fashioned bottle brush it gives your digestive tract a good internal scrubbing. This helps keep your innards nice and clean!
Insoluble fiber is found in whole grains, nuts, and seeds, and the skins of vegetables and fruit, and green vegetables.
How Much Fiber do You Need?
The RDA (recommended daily allowance) for fiber is around 35 grams per day, split evenly between soluble and insoluble varieties.
Your total daily fiber requirement varies according to your age, weight and the amount of food you are eating which is why you may often see a recommended range for fiber consumption of 24 to 35 grams. As fiber is calorie free, there is little harm in making sure you hit the upper ranges of this scale.
The recommended intake for fiber according to the US Department of Agriculture (USDA) is as follows:2Age Female Male 2-3 years 14 grams 14 grams 4-8 years 17 grams 20 grams 9-13 years 22 grams 25 grams 14-18 years 25 grams 31 grams 19-30 years 28 grams 34 grams 31-50 years 25 grams 31 grams 51 and older 22 grams 28 grams
What are the Benefits of Fiber?
Despite being calorie and nutrient-free, fiber offers a wide range of health benefits. Fiber helps reduce inflammation, may lowers the risk of chronic disease and cancer, and has a positive impact on digestive health and weight control. 34 Here’s a deeper look at the benefits.
Helps Weight Loss & Keeps You Feeling Full
Fiber is calorie free. This means that foods that contain a lot of fiber such as whole grains, fruits and vegetables are generally lower in calories than foods with less fiber.
To put this in perspective, an apple and a typical cookie both contain around 60 calories. Because much of the mass of the apple is made up from calorie-free fiber and water, compared to sugar and fat in the cookie, the apple is bigger, far more filling and much more satisfying to eat. Most of us can eat a few cookie in a single serving but it’s pretty unlikely you’ll eat the same number of apples!
Filling up on fiber is a great way to prevent overeating. Stretch receptors in your stomach send signals to your brain when it is full, so you know when to stop eating. This message can take as long as 30 minutes to be sent and delivered. Fibrous foods cause greater gastric distension than non-fibrous foods. Simply put, it means you feel fuller, quicker which results in your brain getting the “stop eating” signal sooner. This limits your potential for overeating and can help weight loss.56
Helps Control Blood Sugar Levels
Fiber keeps food in your stomach for longer. By delaying gastric emptying, fiber also helps to control your blood glucose levels. Large fluctuations in blood glucose can trigger corresponding fluctuations in insulin levels.
Roller coaster blood glucose levels play havoc with your hunger. A rapid drop in blood glucose can often result in cravings for carbohydrate (one reason never to go grocery shopping on an empty stomach!). By slowing down stomach emptying, soluble fiber helps ensure that your blood sugar levels remain relatively stable.78
Maintains Digestive Health
The hollow tubes of your intestines are made of smooth muscle and like the muscles of your arms or legs, benefit from a regular workout. Fiber provides the means to exercise your digestive system. A diet devoid of fiber will result in poor intestinal health in the same way that a lack of exercise will result in a flabby, weak body.
To push food though your digestive system, the smooth muscular tubes that make up your digestive tract must squeeze inward in an action called peristalsis. Picture a snake swallowing an egg and the wave-like undulations as the snake squeezes the egg down the length of its body – that’s peristalsis.
Low fiber foods do not travel though your hollow digestive tubes very easily. A large amount of pressure is required to push food along. Imagine trying to get the very last bit of toothpaste out of the tube – it’s a real challenge! Fiber adds bulk to your food and, consequently, it passes though your digestive system much more easily and with far less pressure.
Easy food passage and reduced food transit time (the time it takes from ingestion to elimination) has a major impact on digestive health and is strongly linked to a lower incidence of diverticular disease, also known as diverticulitis. This is a painful and serious medical condition where bacteria-filled bulges develop in the walls of your intestines.
By consuming adequate fiber, intestinal pressure is kept to a minimum, and bacteria and other buildup is cleaned out, improving gut health and helping to reduce the risk of developing colon cancer, hemorrhoids, and diverticulitis.912
What Foods Are High in Fiber?
Fiber might be calorie free but it’s very important for digestive health. Eat plenty of unrefined carbohydrates, fruits and vegetables and you should have no problems hitting your daily fiber requirements. Here’s a list of some high-fiber foods.
| Food | Serving size | Total fiber (grams) |
|---|---|---|
| Raspberries | 1 cup | 8.0 |
| Apple, with skin | 1 medium | 4.8 |
| Banana | 1 medium | 3.2 |
| Green peas, cooked | 1 cup | 8.8 |
| Broccoli, cooked | 1 cup chopped | 5.2 |
| Potato, baked, with skin | 1 medium | 4.0 |
| Split peas, cooked | 1 cup | 16.4 |
| Lentils, cooked | 1 cup | 15.6 |
| Black beans, cooked | 1 cup | 15.0 |
| Chia seeds | 1 Tbsp | 4.1 |
| Bran flakes cereal | 1/2 cup | 3.6 |
| Quinoa, cooked | 1 cup | 5.0 |
| Popcorn | 2 cups | 3.8 |
| Brown rice, cooked | 1 cup | 3.1 |
| Bread, whole-wheat | 1 slice | 1.9 |
Source: USDA13
