Eat more fiber. You have no doubt heard this advice many times before and for a good reason. Eating more foods high in dietary fiber is one of the best things you can do for your health.
What is dietary fiber?
Dietary fiber is not one thing, but is a group of carbohydrates that are not easily digested by our body. Our enzymes cannot break them down, so they pass through the small intestine, largely unchanged. Once they reach the colon some fibers become fuel for the friendly bugs that live there – your microbiota – while others pass straight through, acting like a kind of broom, sweeping through your gut helping to keep you regular.
Importantly these different types of fiber have very different effects on your body and eating a broad range of fiber types brings the most benefit. Fiber plays an important part in digestive health and is fundamental for regular bowel movements. But fiber has many more benefits. It can help you feel fuller for longer, improve blood cholesterol levels and even lower blood sugar levels. These benefits can translate into helping to maintain a healthy weight and lowering your risk of diabetes, heart disease and bowel cancer.
You will find fiber in plant foods such as wholegrain cereals, fruits, vegetables, nuts and legumes. Eating a broad range of these foods in plentiful amounts is the best way to ensure you get enough overall fiber and a good range of different fiber types.
How much to eat
How much to eat
It is the position of the American Dietetic Association that the public should consume adequate amounts of dietary fiber from a variety of plant foods. Dietary Reference Intakes recommend consumption of 14 g dietary fiber per 1,000 calories, or 25 g for adult women and 38 g for adult men, based on studies showing protection against cardiovascular disease.
Some tips on getting more fiber in your diet include:
- choosing wholegrain, whole meal and high fiber varieties of grain-based foods
- loading up on legumes such as lentils, kidney beans and chickpeas
- having two pieces of fruit and five servings of vegetables a day
- Swap processed snacks with fiber-rich alternatives and read nutrition labels on packaged foods – a food with 3 grams of fiber per serve is a good source of fiber.
Soluble vs insoluble fiber
The two main types of dietary fiber in our diet are soluble and insoluble fiber. Soluble fiber dissolves in water, forming a gel-like substance, which can bypass digestion in the small intestine. Gut bacteria can then easily ferment most soluble fibers and boost gut bacteria populations.
This viscous gel also slows down the digestion of starch and sugars in the meal, in turn slowing down their absorption, helping to blunt the rise in blood sugar. Soluble fiber also binds to cholesterol in bile, flushing it out of the body and helping to lower the more harmful LDL-cholesterol in the blood. Foods high in soluble fiber include barley, oats, legumes, vegetables and fruits.
Insoluble fiber is the “tougher matter” and isn’t broken down in the small intestine. It is mostly responsible for keeping things moving along the gut. When insoluble fiber reaches the large bowel, it absorbs a lot of water and increases the bulk of the stool. It also makes the stool softer, increasing the speed and ease with which it passes through your bowel. This all adds up to helping prevent constipation and keeping you regular. This type of fiber is found mainly in wholegrain cereal foods, wheat bran and vegetables.
Most of the starch we eat is easily digested and absorbed by the body. But there are some forms of starch that are resistant to digestive attack and pass through to the large intestine. Once there, the resistant starch is broken down and fermented by bacteria.
The result of resistant starch fermentation is a range of health benefits such as a mild laxative effect, encouraging the growth of healthy bacteria, and producing compounds called short-chain fatty acids, which promote intestinal health.
Foods high in resistant starch include oats, cooked and then cooled rice and potatoes, legumes and green bananas.
The best reason to be eating more fiber is for what it can do for our resident gut bacteria – the microbiota. These bacteria are recognized to play an important part in our health. A prebiotic is the name given to fiber that can have a favorable health benefit through the action of gut bacteria.
Prebiotics act as a fuel to enhance the growth or activity of beneficial bacteria such as Bifidobacteria and Lactobacillus. Other benefits of prebiotics include improvement in the health of the lining of the gut, boosting immune function, and reducing the growth of potentially harmful bacteria.
One potential short-term downside from the by-products of fiber fermentation is too much gas. That is why foods high in fermentable fiber can sometimes cause flatulence and stomach discomfort, especially in someone not used to eating a lot of fiber. By slowly increasing the amount of foods high in fiber in your diet, you’ll find this settles down in a few weeks as your body adapts to the new food environment.