Hummingbird Metabolism Unique in Burning Glucose and Fructose Equally

Hummingbird metabolism is a marvel of evolutionary engineering. These tiny birds can power all of their energetic hovering flight by burning the sugar contained in the floral nectar of their diet. Now new research from the University of Toronto Scarborough (UTSC) shows these tiny birds are equally adept at burning both glucose and fructose, which are the individual components of sucrose; a unique trait other vertebrates cannot achieve. "Hummingbirds have an optimal fuel-use strategy that powers their high-energy lifestyle, maximizes fat storage, and minimizes unnecessary weight gain all at the same time," says Dr. Kenneth Welch, assistant professor of biological sciences at UTSC and an expert on hummingbirds. Dr. Welch and his graduate student Chris Chen, who is co-author of the research article, fed hummingbirds separate enriched solutions of glucose and fructose while collecting exhaled breath samples. The researchers found that the birds were able to switch from burning glucose to fructose with equal facility. "What's very surprising is that, unlike mammals such as humans, who can't rely on fructose to power much of their exercise metabolism, hummingbirds use it very well. In fact, they are very happy using it and can use it just as well as glucose," says Dr. Welch. Hummingbirds require an incredible amount of energy to flap their wings 50 times or more per second in order to maintain hovering flight. In fact, if a hummingbird were the size of a human, it would consume energy at a rate more than 10 times that of an Olympic marathon runner. They are able to accomplish this by burning only the most recently ingested sugar in their muscles while avoiding the energetic expenditure of first converting sugar into fat.
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