I’m an addict. My addiction? The same stuff used by diabetics, the overweight, those with sweet tooths, and the chronically sleep-deprived: diet soda.

Thus it is with mixed feelings that I report this year has been a game-changer for understanding what diet soda’s artificial sweeteners do to our bodies.

The science of sweets finally moved from correlation to causation. And it isn’t pretty.

The short version: Artificial sweeteners like aspartame and sucralose can contribute to some of the health maladies that we’re using them to avoid. It’s like smoking “light” cigarettes to combat lung cancer.

Diet sodas and other diet drinks are pivotal for understanding how such sweeteners impact health because they are far and away the biggest delivery devices for artificial sweeteners. And their lesson is relevant to all of us who eat processed foods—because artificial sweeteners are becoming more ubiquitous, even in non-diet and non-sugar-free products.

Coloradans guzzle a tremendous amount of soda, “teas” and energy drinks. Why? Because they taste good and most provide a nice dose of everyone’s favorite addictant: caffeine. Increasingly people favor diet or sugar-free versions of these beverages because artificial sweeteners don’t add calories.

They’re supposed to satisfy our body’s craving for “sweet” while helping us avoid gaining weight, raising our blood sugar, or increasing diabetes risk. But like caffeine, they can become addictive. Maybe that’s why I crave a diet soda before breakfast every morning!

On the surface, Colorado seems to be in decent shape (pun intended) because its diabetes and obesity rates are among the lowest in the nation. That said, our diabetes rate (7%) is double what it was 20 years ago, and our obesity rate (21%) has tripled over that interval. We are at what are called “epidemic” levels. Colorado’s increases mimic increases occurring worldwide in developed nations, and parallel the rise in use of artificial sweeteners. But this is merely a correlation, not a causation.

The causation has been recently documented by studies in humans, mice and rats. Scientists have learned that artificial sweeteners radically alter the ecosystem of bacteria that thrives in our guts. This occurs because most artificial sweeteners pass undigested into our intestines, where they then directly encounter our gut’s milieu of bacteria.

Our gut bacteria are very important. In the same way that we use yeast (i.e., microscopic fungi) to raise bread and brew beer, our gut contains a diverse community of bacteria that processes food that our body cannot break down on its own, produces necessary nutrients like vitamins, and regulates the production of compounds that signal our brain and maintains our blood chemistry. They even produce gas now and then.

We have a symbiotic relationship with these gut bacteria—our survival depends on them and their survival depends on us. But artificial sweeteners can wreak havoc on this bacterial ecosystem, throwing it out of balance. For example, saccharin (common in fountain drinks, salad dressing, canned fruit, baked goods, and Sweet‘N Low), shifts the bacterial ecosystem to one that decreases your body’s ability to regulate the glucose (i.e., sugar) in your blood. It does so by increasing the ability of certain groups of bacteria to break down certain compounds in your food —this is thought to cause a chain reaction which begins with increased energy extraction, is followed by fatty acid production, and ends with glucose synthesis. This sugar ends up in your blood.

The same end-effect occurs when we ingest aspartame (found in Coke Zero, Diet Coke, Diet Pepsi, energy drinks, gum, yogurt, Equal and Nutrasweet) and sucralose (common in Snapple, Arizona teas, fruit sodas, energy bars, and Splenda). But the double-whammy is that regular consumption of artificial sweeteners also causes our bodies to become less adept at reducing blood sugar levels. Thus consumption of artificial sweeteners can lead to type II diabetes and exacerbate issues faced by existing diabetics.

All this can happen at and below approved FDA dosages of sweeteners, and effects may begin to occur in humans as soon as a week after regular ingestion begins.

But what about stevia? It is a minor but rising player in the artificial sweetener world. Although often touted as “natural,” it is about as natural as the oil you put in your car. Both substances may originally come from plants, but both are highly derivative chemical compounds, with newer stevia compounds being refined by GMO-catalyzed reactions. Keep your eyes peeled for forthcoming results on its impact on human health.

The good news is that the gut’s microbial ecosystems vary among individuals, and some appear to be more resistant to artificial sweeteners than others. Does this mean that a new nutritional world is coming? If so, it could be one that makes individualized dietary recommendations based on the composition of one’s microbes.

So, a New Year’s resolution. I want to wean my diet-drink habit. But first maybe I’ll try getting 8 hours of sleep.

James Hagadorn, Ph.D., is a scientist at the Denver Museum of Nature & Science. Suggestions and comments welcome at jwhagadorn@dmns.org.