Fiber is the indigestible carbohydrate content of food, and plays important roles in cultivating vibrant health, especially in our digestive system.
Nutritional experts are continually advising us to include more fiber in the diet. We’ve been told we don’t get enough (1), and eating more fiber is supposed to have benefits across the board, from preventing cancer and heart disease to lowering cholesterol levels.
Government recommendations say women should eat 25 grams of fiber daily, and men need more at 38 grams. (2)
Dietary fiber is an important part of a well-rounded eating plan, but the reasons for including plenty of high-fiber foods are more complex than you might think.
Two kinds of fiber are found in the foods we eat; water-soluble fiber obviously dissolves in water, and insoluble fiber does not. Soluble fiber is digested by bacteria in the gut, and this process has a number of beneficial effects on the system. (3)
The soluble fiber found in foods like nuts, seeds, oat bran, lentils, beans and certain fruits and vegetables attracts water and turns to a gel, slowing digestion. The insoluble fiber found in foods like whole grains and vegetables bulks up the stool, and may help foods pass through the digestive system more quickly. (4)
A Symbiotic Relationship: Fiber and Gut Bacteria
Each of us has around a hundred trillion gut flora living in our digestive tract, ten times as many as the number of cells in our bodies. Gut flora enjoy a safe environment, and in turn, perform services for the body it can’t do on its own.
Since most nutrients are absorbed into the bloodstream quickly, intestinal bacteria are last in line to get the goodies from food we eat. Gut bacteria have the ability to digest fiber, so when the fiber from our diets finally makes it to the large intestine, they go to work digesting what’s been moved along mostly unchanged up to that point.
Prebiotics are a byproduct of this digestion, which increases what’s called the “friendly” bacteria population; when certain species of bacteria thrive in this inner environment, they can positively or negatively affect ratios of lean body mass to body fat. (9)
Butyrate is one of these byproducts, and has been associated with improved colon health. (10, 11) The short-chain fatty acids produced by the digestion of fiber appear to have positive influences on patients with Crohn’s disease and irritable bowel syndrome. (12)
Blood Sugar Regulation and Weight Control
Different kinds of fiber can have different effects on digestion, as well as on sensitive regulatory processes like blood sugar levels. High-fiber foods are usually lower on the glycemic index, so even vegetables high in natural sugars like sweet potatoes, carrots, parsnips, and beets don’t cause significant spikes in blood sugar because it takes longer to digest them. (13)
Low-fiber foods are often higher on the glycemic index, which can cause problems for diabetics and others who want to avoid the harmful effects of blood sugar spikes.
Foods high in fiber take up more space in the stomach, causing a feeling of satiation, which sends the signal to stop eating. The obvious result of this effect is that a focus on high-fiber foods in the diet may result in a lower overall intake of calories.
In one recent study, women were randomly assigned to follow two diets; one was a standard low-fat diet, and the other diet allowed the consumption of as many high water content fruits and vegetables as the subjects desired.
Both groups lost weight: about 14 pounds average for the low fat group, and 17 pounds for women who ate their fill of added foods, all of which were rich in fiber. The women eating plenty of fruits and veggies ate more food by volume, but consumed fewer total calories. They never felt hungry. (14)
Glucomannan, a water soluble fiber supplement derived from the elephant yam, has shown promise as an effective weight-loss supplement. This super-fiber will absorb 50 times its own weight in water, so when taken before a meal with a glass of water, it puffs up in the stomach, creating a full feeling.
Weight-loss supplements made with glucomannan were tested during a 5-week trial with 176 overweight subjects who followed a low-calorie diet. Results were compared to a control group taking placebos, and those who used the supplement dropped up to 6 more pounds than the control group. (15)
Including plenty of dietary fiber in meals also prolongs the sensation of fullness, which can be helpful in achieving weight-loss goals. (16)
Scientists continue to study the data, but it also appears an abundance of friendly gut bacteria is associated with a leaner Body Mass Index (BMI). (17)
Preventing Chronic Diseases
Fiber can positively affect cholesterol levels and other vital health markers. (18)
Research suggests that eating more fiber may be a contributing factor to why plant-based diets have been successful in dropping cholesterol levels, as well as triglyceride measurements and blood pressure. These conditions jack up the risk of coronary heart disease, so upping fiber intake may be useful in treating patients at high risk for cardiovascular problems. (19)
The World Cancer Research Center recommends a plant based diet for decreasing the risk of developing cancer, noting that high fiber intake is especially important in preventing bowel cancer. (20)
Adequate dietary fiber has been associated with a reduction in the risk of developing cardiovascular disease. (21) A study report issued by the National Institutes of Health tracked the health and dietary habits of 50,000 men and women in Japan over 14 years; those who consistently included more fiber in their diets had a lower incidence of cardiovascular disease. (22)
Fiber feeds friendly bacteria in the gut that help keep everything functioning smoothly as digestion processes take place. While this may be part of the reason why eating a high-fiber diet appears to be a healthy choice, many other factors are likely involved. It may take many years and numerous studies to ferret out the particulars.
Summary: Whatever the details, it looks like a safe bet to keep those high-fiber foods on your plate.