Dietary fiber is highly beneficial for health, including its role in preventing cardiovascular diseases, maintaining gut health, and preventing colorectal cancer. However, modern dietary habits often result in insufficient intake of dietary fiber. Strengthening and optimizing the intake of dietary fiber in our diets can bring significant benefits to future health maintenance[1].
What is Dietary Fiber?
The European Food Safety Authority (EFSA) defines dietary fiber as indigestible carbohydrates along with lignin, including non-starch polysaccharides, cellulose, pectins, oligofructose, and resistant starch, among others[4].
Dietary fiber is composed of indigestible carbohydrates, typically derived from plant-based foods, and mainly consists of polysaccharides[3]. Carbohydrates are chemically classified based on their molecular size. While sugars (1-2 monomers) and most oligosaccharides (3-9 monomers) are digestible, polysaccharides (≥10 monomers) are usually indigestible because the human body lacks the necessary digestive enzymes.
Dietary fiber is considered a prebiotic, as gut probiotics can metabolize it to produce beneficial compounds for the body. This includes promoting the growth of beneficial bacteria, regulating appetite, and inhibiting chronic intestinal inflammation. Generally, dietary fiber can be categorized into soluble and insoluble fiber. Soluble fiber is primarily found in fruits and vegetables, while sources of insoluble fiber are mainly grains and whole wheat products[5].
The Benefits of Dietary Fiber
1. Regulating Blood Sugar
Both diabetes education and various national nutrition associations emphasize increasing the intake of dietary fiber for diabetes patients to improve insulin resistance and blood sugar metabolism, leading to better blood sugar control[5]. Analytical studies have found that adding dietary fiber to the diet of type 2 diabetes patients can significantly reduce fasting blood glucose levels and HbA1c[6].
Clinical research has discovered that supplementing subjects with dietary fiber enhances the response of glucose-dependent insulinotropic polypeptide (GIP), which is insulin and glucose-dependent, thereby regulating blood sugar levels[7]. Another clinical study showed that daily supplementation of 30 grams of dietary fiber helped improve insulin sensitivity[8].
2. Regulating Blood Lipids
Numerous studies have confirmed that dietary fiber can lower total cholesterol and low-density lipoprotein cholesterol (LDL-C), aiding in the treatment of cardiovascular diseases. Analytical research results have indicated that dietary fiber can lower the incidence of cardiovascular diseases related to atherosclerosis, whether in patients with hypercholesterolemia or in healthy populations[9].
Clinical study outcomes revealed that supplementing subjects with dietary fiber resulted in significant reductions in total cholesterol, LDL-C, and the ratio of LDL to high-density lipoprotein (HDL), indicating an improvement in blood lipid status due to dietary fiber intake[10].
3. Regulating Blood Pressure
In recent years, many studies have found that consuming dietary fiber can help regulate blood pressure. Evidence of this has been observed in both animal and human clinical experiments[11]. Analytical studies found that additional dietary fiber intake can significantly lower systolic and diastolic blood pressure in subjects, potentially reducing the risk of cardiovascular diseases by improving blood pressure conditions[12].
Another clinical study observed that providing high blood lipid patients with a high dietary fiber diet resulted in significant reductions in systolic and diastolic blood pressure, as well as a significant decrease in mean arterial pressure[13].
4. Weight Management
Dietary fiber can promote a feeling of fullness through hormonal and colonic effects, reducing food intake. Hormonal effects involve regulating insulin secretion to promote satiety, while colonic effects result from the fermentation of short-chain fatty acids to generate a sense of fullness, simultaneously assisting in regulating insulin secretion. Additionally, chewing and the volume produced by dietary fiber intake contribute to a sense of satiety[14] [15].
The majority of studies indicate that increasing dietary fiber intake enhances post-meal satiety and reduces subsequent feelings of hunger. This effect is even more pronounced in obese individuals, where the inhibitory effects on calorie intake and the degree of weight loss due to increased dietary fiber intake are observed more significantly[16].
5. Improving Gut Health
Dietary fiber, typically derived from plant-based foods, acts as a prebiotic, providing nourishment for beneficial gut bacteria. This promotes the growth of beneficial bacteria, leading to changes in the gut microbiota[17]. Clinical studies involving overweight or obese adults who supplemented their diets with dietary fiber found significant increases in microbial metabolites, such as short-chain fatty acids and primary bile acids, indicating the utilization of dietary fiber by gut microbiota to produce beneficial substances that contribute to gut health[18].
6. Preventing Cancer
In recent years, the association between dietary fiber intake and colorectal cancer has been extensively studied. Increased fiber intake is believed to dilute carcinogenic substances in the intestines and reduce their dwell time. Furthermore, the fermentation of dietary fiber by gut bacteria produces short-chain fatty acids with anticancer properties. Research also suggests a negative correlation between dietary fiber intake and the risk of colorectal cancer[19].
Analytical studies found that a daily intake of 10 grams of dietary fiber can reduce the risk of colon and rectal cancer by 10%, with a decreasing cancer risk associated with higher intake levels[20]. Additionally, dietary fiber intake has been linked to a reduced risk of ovarian cancer, with a 3% reduction in risk for every 5-gram increase in dietary fiber intake[21].
Which Foods Contain Dietary Fiber?
Whole grains: Unrefined rice, barley, corn, oats, wheat, buckwheat, millet, brown rice, purple rice, etc.
Legumes and animal products: Black beans, edamame, tofu, soy milk, etc.
Vegetables: Red amaranth, red spinach, water spinach, spinach, rapeseed, broccoli, carrots, pea pods, Chinese artichoke, bitter gourd, dried shiitake mushrooms, garlic, etc.
Fruits: Passion fruit, guava, kiwi, sugar apple, sweet peach, orange, etc.
Fats and seeds: Flaxseed, black sesame seeds, shelled pistachios, pumpkin seeds, red peanuts, etc.[22] [23]
Difference Between Soluble and Insoluble Dietary Fiber
There are two main types of dietary fiber: soluble and insoluble. Soluble dietary fiber can dissolve in water and forms a viscous substance in the stomach, including pectin, fructans, and resistant starch. Insoluble dietary fiber does not form a viscous substance and includes lignin, cellulose, and hemicellulose. While most dietary fiber is metabolized and fermented by gut microbes, soluble fiber is often more readily fermented by gut microbes compared to insoluble fiber[5] [23][24].
- Soluble dietary fiber has benefits such as delaying gastric emptying, increasing satiety, improving constipation, and serving as a source of nutrients for beneficial gut bacteria.
- Insoluble dietary fiber increases satiety, improves constipation, increases stool volume, and helps prevent diverticulitis[22].
Side Effects of Excessive Dietary Fiber Consumption
In general, there is currently no evidence that daily dietary fiber intake has negative effects on the human body. However, it might lead to bloating and gas in some individuals, and in more severe cases or among those unaccustomed to a high-fiber diet, it might result in abdominal pain and diarrhea.If there are concerns about supplementing dietary fiber, it’s advisable to consult with a family physician or a registered dietitian[25].
