Dietary Fiber and Its Effects

Posted on Sep 4, 2024 in Biology

Dietary Fiber: Function, Sources, and Benefits

Background

  • Dietary fiber, previously known as “roughage,” refers to substances in plant foods that are not fully broken down by human digestive enzymes.

  • Initially, it was believed that dietary fiber was entirely indigestible and provided no energy.

It is now understood that some fiber undergoes fermentation in the large intestine by gut bacteria, producing short-chain fatty acids and gases.

  • These fatty acids are absorbed into the bloodstream and provide a small amount of energy.

  • The amount of gas produced varies depending on the type of fiber consumed and the gut bacteria present. After a significant increase in fiber intake, some individuals may experience symptoms like abdominal distension, discomfort, and flatulence (methane, hydrogen, and carbon dioxide). However, the large intestine and gut bacteria gradually adapt to the increased intake, and symptoms typically decrease.

  • Dietary fiber includes waxes, lignin, and polysaccharides such as cellulose and pectin.

Function

  • Aids in energy intake control

  • Reduces the risk of obesity

The role of dietary fiber in energy intake regulation and obesity prevention is linked to its unique physical and chemical properties that contribute to early satiation signals and enhanced or prolonged satiety signals, resulting in meals with reduced energy density.

Main Types

Soluble Fiber

  • Dissolves in water

  • Readily fermented in the colon into gases and physiologically active byproducts

  • Can be prebiotic and viscous

  • Tends to slow down the movement of food through the digestive system

Insoluble Fiber

  • Does not dissolve in water

  • Can be metabolically inert and provide bulking, or it can be prebiotic and ferment in the large intestine

  • Bulking fibers absorb water as they move through the digestive system

  • Tends to accelerate the movement of food through the system

  • Fermentable insoluble fibers mildly promote stool regularity, but they can be readily fermented in the colon into gases and physiologically active byproducts

Effects of Dietary Fiber

Effects
Increases food volume without increasing caloric content to the same extent as digestible carbohydrates, providing satiety and potentially reducing appetite.
Attracts water and forms a viscous gel during digestion, slowing stomach emptying and intestinal transit, shielding carbohydrates from enzymes, and delaying glucose absorption, which stabilizes blood sugar levels.
Lowers total and LDL cholesterol, potentially reducing the risk of cardiovascular disease.
Regulates blood sugar, potentially reducing glucose and insulin levels in individuals with diabetes and lowering the risk of developing diabetes.
Speeds up the passage of food through the digestive system, promoting regular bowel movements.
Adds bulk to the stool, alleviating constipation.
Balances intestinal pH and stimulates the production of short-chain fatty acids through intestinal fermentation, potentially reducing the risk of colorectal cancer.

Advantages and Disadvantages

  • Advantages: Production of beneficial compounds during the fermentation of soluble fiber and insoluble fiber’s ability to increase bulk, soften stool, and shorten intestinal transit time.

  • Disadvantages: Potential for significant intestinal gas production and bloating. Constipation can occur if insufficient fluid is consumed with a high-fiber diet.

Sources of Dietary Fiber

  • Soluble: Legumes (e.g., peas, soybeans), oats, rye, barley, some fruits (e.g., figs, avocados, plums, bananas, apple skin), vegetables (e.g., broccoli, carrots, onions, sweet potatoes), nuts (e.g., almonds)

  • Insoluble: Whole grain foods, wheat and corn bran, legumes (e.g., beans and peas), nuts and seeds, potato skins, vegetables (e.g., green beans, cauliflower, zucchini), fruits (e.g., unripe bananas, grape skins, tomato skins)

Recommendations

  • Recommended daily intake:

    • Adults: 20-35g/day
    • Children: Age in years + 5g/day

  • Average intake by the population: 12-18g/day

Preventive Effects of Dietary Fiber

  • Increases fecal bulk and helps prevent constipation by reducing fecal transit time in the large intestine.

  • Reduces blood pressure.

  • Improves gastrointestinal health.

  • Improves glucose tolerance and insulin response after meals.

  • Increases colonic fermentation and short-chain fatty acid production.

  • Positively modulates colonic microflora.

  • Reduces hyperlipidemia, hypertension, and other coronary heart disease risk factors.

  • Reduces the risk of developing certain cancers, particularly colon cancer.

  • Increases satiety and contributes to weight management.