4.1.5: 5 Dietary Fiber and Microbes in the Human Gut

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The Importance of Fiber Overall and for the Gut Microbiome

In addition to these nutrients that contribute to particular functions within the human body, fiber is the mostly undigestible component of food that moves through the human digestive tract but also provides remarkable benefits. Undigestible cell wall components of plant foods (fruit membranes, bean and grain seed hulls, most of the plant cell wall, etc.) are examples of dietary fiber. In addition to its famous role in avoiding constipation by moving masses of foodstuffs through the digestive tract as a bulking agent, fiber helps to feed beneficial gut bacteria that produce beneficial substances. Over the last few decades fiber consumption associated with the benefits of avoiding certain cancers, heart disease, and diabetes. Emerging knowledge regarding fiber highlights the role played by the gut microbiome --many billions of non-human cells that inhabit our digestive tract in promoting human health and avoiding disease. These cells are more in number than the human cells in our body, due to the small size of bacteria compared to human cells. Much like the other areas of nutrition described here, the importance of fiber links directly to the importance of eating a varied diet with whole grains, legumes, fruits, and vegetables. It is interesting to view fiber and these microbes not as a direct nutrient for human life processes, but as a "helper nutrient" or "catalyst" for human nutrition. Dietary fiber is relatively inert as a source of protein, minerals, or vitamins, but helps our digestive system do its job.

Optional Reading

For more on the role of fiber and nutrition generally in an accessible format, you can see the following page: "Dietary Fibre" from the British Nutrition Foundation.

Knowledge Check

Human Nutrition Basics: Choose the nutrient or diet component that matches the function or characteristic.

1) Most important as a mineral nutrient involved in growth, healing, and disease resistance.

Iron
Vitamin A
Carbohydrate
High-quality Fats
Zinc

2) These sources contribute to human uptake/synthesis: eggs, carrots, orange-fleshed sweet potatoes, collards.

Iron
Protein
Carbohydrates
Vitamin C
Vitamin A

3) Interacts positively to promote iron uptake when eaten in meals with plant-derived iron.

Protein
Zinc
Vitamin C
Carbohydrates
High-quality fats

4) Considered most importantly as energy sources for respiration within all cells of the body.

Iron
Protein
Vitamin C
Carbohydrates
Zinc

5) Important for hemoglobin in blood; deficiency causes anemia.

High-quality fats
Protein
Iron
Zinc
Vitamin A

6) Consumption is often analyzed as nine essential amino acids.

High-quality fats
Zinc
Protein
Vitamin C
Carbohydrates

7) Plant-based oils are often thought of as this.

High-quality fats
Protein
Zinc
Carbohydrates
Vitamin A