Dietary Fiber

Dietary fiber or roughage is the indigestible portion of food derived from plants. It has two main components: Soluble fiber, which dissolves in water, is readily fermented in the colon into gases and physiologically active byproducts, and can be prebiotic and viscous

Types

• Soluble fiber, which dissolves in water, is readily fermented in the colon into gases and physiologically active byproducts, and can be prebiotic and viscous.
• Insoluble fiber, which does not dissolve in water, is metabolically inert and provides bulking, or it can be prebiotic and metabolically ferment in the large intestine. Bulking fibers absorb water as they move through the digestive system, easing defecation.

Measurement of dietary fiber

In its simplest terms, dietary fiber content in a sample is measured in the laboratory by what is called an enzymatic-gravimetric method.

After defatting, a food sample is treated with enzymes that mimic the digestive process in the human small intestine.

Digestible carbohydrates are broken down into simple sugars and removed from the sample by precipitation and filtration. This mimics absorption of these sugars in the body.

The non-digestible precipitate contains the dietary fiber but also contains protein and inorganic material. These should not be included in dietary fiber so protein and inorganic material must be measured separately and subtracted from the weight.

Dietary fiber health benefits

What are the specific health advantages that exist for diets containing high fiber foods?

Blood sugar: Certain types of dietary fiber may help to slow your body’s breakdown of carbohydrates and the absorption of sugar, helping with blood sugar control. This aspect could be particularly important for those people suffering from diabetes.

Heart health: An inverse association has been found between fiber intake and heart attack, and research shows that those eating a high-fiber diet have a 40 percent lower risk of heart disease. Clearly linked to this is the finding that increased fiber intake can lower blood cholesterol

Colon cancer: There are a number of epidemiological and experimental studies that suggest dietary fiber can play a role in colon cancer prevention.

Stroke: A strong correlation between increased fiber intake and reduced first stroke rate has been identified in a recent study of patients in the US, Northern Europe, Japan and Australia.

Weight loss and management: Fiber supplements have been shown to enhance weight loss among obese people.⁶ This is likely to be because certain types of fiber increases feelings of fullness.

Diverticulitis: Dietary fiber (especially insoluble) may reduce your risk of diverticulitis – an inflammation of polyps in your intestine – by 40 percent.

Hemorrhoids: A high-fiber diet certainly helps in the treatment of constipation and as a result may lower the risk of hemorrhoids

Irritable bowel syndrome (IBS): Fiber may provide some relief from IBS

Gallstones and kidney stones: A high-fiber diet may reduce the risk of gallstones and kidney stones, likely because of its ability to help regulate blood sugar.

Dietary fiber regulations

CODEX Alimentarius was founded in 1963 as part of the World Health Organisation Food and Agriculture Organisation (WHO/FAO) and is the international body that sets guidelines for national regulatory authorities. In 2009, they finally reached consensus upon a definition of dietary fiber after almost 20 years of deliberation:

Nutrition Facts Labelling

Acceptance of the CODEX definition by a national governing body has important implications for compliance with nutrition facts labelling regulations. As AOAC 2009.01 is the only analytical method that can accurately measure dietary fiber as defined by CODEX, the onus is now placed on food manufacturers to ensure that the dietary fiber content on their product labels agrees with the values obtained with AOAC method 2009.01.  This can have significant consequences for companies wishing to make specific health claims based on dietary fiber content. The rules and regulations relating to this topic can vary from country to country. The United States and European Union are examined as test cases:

United States Dietary Fiber Nutrient Content Claims

Claims made on food product packaging need to be tightly regulated. It is important that the consumer is not misled in their assessment of how healthy a particular food product is. Nutrient content claims are dependent on three factors:

The daily value (DV) is the FDA’s recommended daily amount of an ingredient. The DV for dietary fiber is 25g for a 2000 calorie diet.

The reference amount customarily consumed (RACC) is set by the FDA and is basically the guide serving quantity of the product in question.

Claim thresholds are set by the FDA and are based on the percentage of the DV present in the RACC for a given product.

10-19% of DV in RACC allows “good source” claim.

20+% of DV in RACC allows “high” or “excellent” source claim.

As an example, the RACC for rice is 45g dry weight so greater than (2.5g / 45g = 5.6%) fiber content allows a food manufacturer to make good source claim.

Dietary Fiber Health Claims

Four separate health claims have been approved by the FDA on fiber containing products. These health claims fall under the categories:

• Fiber-containing foods and cancer
• Fiber-containing foods and coronary heart disease
• Fruits and vegetables and cancer
• Soluble fiber from certain foods and risk of coronary heart disease

There are strict guidelines governing when one of these claims can be made for a given product

Low fat diets rich in fiber-containing grain products, fruits and vegetables may reduce the risk of some types of cancer, a disease associated with many factors.”