Bacteria in our gut gobble up things like sugars and fatty acids, which they can break down either through respiration or fermentation. Respiration provides a bigger energy kick.
我们内脏里的细菌会吞噬糖类和脂肪酸一类的物质，它们通过呼吸作用和发酵作用可以分解此类物质。
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Because essentially no oxygen is available in our intestines, the beneficial bacteria that reside there tend to use fermentation, which is less efficient than respiration for obtaining energy.