Opinion Review
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World J Gastroenterol. Dec 7, 2021; 27(45): 7784-7791
Published online Dec 7, 2021. doi: 10.3748/wjg.v27.i45.7784
Humans have intestinal bacteria that degrade the plant cell walls in herbivores
Shunji Fujimori
Shunji Fujimori, Department of Gastroenterology, Chiba Hokusoh Hospital, Nippon Medical School, Chiba 270-1694, Japan
Author contributions: Fujimori S contributed to the writing of this paper.
Conflict-of-interest statement: The author declares no conflict of interest.
Open-Access: This article is an open-access article that was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution NonCommercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: https://creativecommons.org/Licenses/by-nc/4.0/
Corresponding author: Shunji Fujimori, AGAF, MD, PhD, Director, Department of Gastroenterology, Chiba Hokusoh Hospital, Nippon Medical School, 1715 Kamagari, Inzai-City, Chiba 270-1694, Japan. s-fujimori@nms.ac.jp
Received: May 3, 2021
Peer-review started: May 3, 2021
First decision: June 12, 2021
Revised: June 22, 2021
Accepted: November 24, 2021
Article in press: November 24, 2021
Published online: December 7, 2021
Processing time: 213 Days and 17.2 Hours
Abstract

The cell walls of plants are mainly made of cellulose and contain a large number of calories. However, the main component, cellulose, is an indigestible plant fiber that is thought to be difficult for humans to use as energy. Herbivores acquire energy through the degradation of cell wall-derived dietary fiber by microorganisms in the digestive tract. Herbivores, especially horses, have a highly developed cecum and large intestine, and plants are fermented for their efficient use with the help of microorganisms. Humans also have an intestinal tract with a wide lumen on the proximal side of the large intestine, in which fermentation occurs. The digestive process of horses is similar to that of humans, and many of the intestinal bacteria found in horses that degrade plants are also found in humans. Therefore, it is thought that humans also obtain a certain amount of energy from cell wall-derived dietary fiber. However, the intake of dietary fiber by modern humans is low; thus, the amount of calories derived from indigestible plant fiber is considered to be very low. Cellulose in the plant cell wall is often accompanied by hemicellulose, pectin, lignin, suberin, and other materials. These materials are hard to degrade, and cellulose is therefore difficult for animals to utilize. If the cell wall can be degraded to some extent by cooking, it is thought that humans can obtain calories from cell wall-derived dietary fiber. If humans can use the calories from the cell wall for their diet, it may compensate for human food shortages.

Keywords: Intestinal flora; Human; Herbivore; Indigestible plant fiber; Cell wall; Calorie

Core Tip: The plant cell wall is mainly composed of cellulose and contains a high number of calories. However, it is classified as an indigestible dietary fiber, and its energy utilization is difficult. Many of the intestinal bacteria found in herbivorous horses that degrade plants are found in humans. Therefore, it is thought that humans can also utilize plant cell walls for energy to some extent. If cell wall-derived dietary fiber can be cooked to make it easier for humans to use, it may compensate for human food shortages.