Fiber is a type of carbohydrate needed from the diet and can be separated into two types; soluble and insoluble. Soluble fiber can dissolve in water, which means it can be fully digested by being turned into a gel like substance. This gel substance gets further broken down into gases and acids by the large intestine and used as fuel for gut bacteria. (1) It helps to lower glucose and blood cholesterol levels. Soluble fiber foods include oatmeal, nuts, beans, apples and blueberries. Insoluble fiber does not dissolve in water. This means that our body can’t digest it fully and passes through our system while remaining intact. It helps to promote regularity and is found in foods like whole wheat bread, brown rice, carrots, cucumbers and tomatoes. (2) Adults need at least 20-30 grams of fiber per day, but most consume only 15 grams. (2) Diets low in fiber can be detrimental to overall health. Research has shown that diets low in fiber can increase the risk of developing certain cancers, type 2 diabetes, heart disease, stroke, high blood pressure, and high cholesterol. (3) It has been shown that increasing fiber intake by 7 grams a day leads to a 7% reduction in risk of developing one of these condition. (4) 7 grams of fiber is like eating an apple with lunch, or a serving of whole grain pasta to replace white pasta at dinner. It isn’t just the intake of fiber that miraculously decreases the risk of these conditions though. As you can see from the list of foods high in fiber, a diet high in fiber means a diet high in whole foods, fruits, vegetables and less meats and processed foods. And of course, a diet high in these things tends to mean overall better health and lower rates of obesity.
It can be difficult to decipher the high fiber foods that aren’t just straight broccoli or apples though. For example, a box of cereal that displays “Made with Whole Grains!” or “Excellent Source of Fiber!” can draw in a consumer who would take the cereal company’s word for it without checking the ingredients. Even if that cereal is high in fiber, chances are it is also high in sugar, cholesterol and fat, which won’t help to combat heart disease, high blood pressure or stroke. (5) One easy way to decide if that cereal or bread is actually high in fiber is the 5-1 rule. (6) To do this you look at the grams of carbohydrates in the item and divide them by the grams of dietary fiber. If the answer is 5 or less and you’ve checked to make sure it isn’t high in sugar or fat than you are good to go.
The under-consumption of fiber is also a concern. Eating a low fiber diet is greatly associated with irregularity and constipation. Dietary fiber increases the size of and softens stools which allows them to move easily and quickly through your system. Soluble fiber also leads to more healthy bacteria in your gut. There are two types of gut bacteria, good and bad. The prebiotics in soluble fiber are a fuel source for the good bacteria so they can grow and function properly. (6) A diet low in fiber doesn’t provide the good bacteria with the fuel source they need so the bad bacteria become overgrown, leading to an inflammatory response. This is the main reason why a low fiber diet is harmful. We need to fiber to fuel our gut bacteria to keep healthy intestines and prevent inflammation.
1.) S M Kuo. The interplay between fiber and the intestinal microbiome in the inflammatory response. Adv Nutr. 2013 Jan1;4(1):16-28. (https://www.ncbi.nlm.nih.gov/pubmed/23319119)