Search of the Week: “why don’t hummingbirds get diabetes”

A male Broad-billed Hummingbird threatens an intruder in his feeding territory.

This week’s featured search topic has been addressed on LB&E previously here and here.

Type 2 diabetes, the disease people are thinking of when they ask such questions (because they’ve been told, wrongly,*⇓ that sugar consumption causes diabetes), is largely a modern human affliction. We eat too much, including highly processed foods full of easily digested simple carbohydrates that flood our bloodstreams with glucose. We exercise too little, contributing to getting fat and staying fat. Our bodies may continue producing insulin to aid in utilization of the glucose in our systems, but over time our cells may stop responding to it.

These issues weren’t much of a problem for our pre-industrial ancestors (even those with a genetic predisposition to diabetes), and they’re still not much of a problem for people living labor-intensive lifestyles and eating traditional diets high in complex carbs, fiber, and other good things.

They’re also not a problem for hummingbirds. More than 40 million years of evolution have adapted these tiny, hyperactive dynamos to a sugar-rich diet. To maintain some of the highest metabolic rates ever measured, hummingbirds must take in enormous amounts of energy. The most energy-dense food available to them is flower nectar. Without it, the tiny, hovering jewels we know and love would never have evolved.

You might say that hummingbirds show three classic symptoms of diabetes: they eat a lot (polyphagia), drink a lot (polydipsia), and pee a lot (polyuria). Of course, these “symptoms” are simply consequences of a high metabolism and water-rich diet. They also have very high blood glucose levels, high enough to cause serious complications in humans, but their absorption and utilization of the sugars in their diet are so efficient that almost none ends up in their urine (as it does in human diabetes patients).

Medical researchers would love to know exactly how hummingbirds avoid the short-term and long-term complications of high blood glucose, but it’s clear that their ability to do so has been honed by natural selection. Any hummingbird that had a serious defect in its ability to absorb and/or metabolize sugar would be dead within days, weeded out of the gene pool.

Here’s an in-depth examination of the issues from the perspective of human health:

Adipose energy stores, physical work, and the metabolic syndrome: lessons from hummingbirds

* Since this post was written, new research has persuaded many members of the medical community that there’s a more direct link between sugar consumption and Type 2 diabetes than decades of propaganda by Big Sugar would have us believe.