Why is there something in Coke Zero that makes you crave sweets more?

Because your palate gets saturated by sweet and as such many things that have a low sugar content are not appealing to you anymore. For example, when I was younger I was the only one in the family who drank soft drinks. Every time my mother made an apple pie it almost tasted sour to my mouth even though the rest of the family found it very sweet and pleasant. Wouldn't you know it, when I stopped with the sweet soft drinks my palate adjusted and I could finally enjoy my mother's low sugar pie

Because it tastes sweet which changes your palette to prefer sweeter things generally. Some of these will likely contain sugar. So you’ll eat more sugar than if you drank water.

Contrary n=1 anecdata:

When I experience aspartame, the host product tastes "wrong", and if I consume more than a wee bit, my stomach gets a bit upset. So, let me ignore that sweetener…

When I use most artificial sweeteners, at first they can seem enjoyable and freeing. A 50:50 blend of Stevia-in-the-Raw and Splenda can seem more like real sugar to me. But with repeated frequent use (say, daily in a mug of tea), I gradually come to feel not an anticipation of something good and satisfying but an expectation of doing something 'empty'. Sweetness in general becomes increasingly distasteful.

Perhaps the distaste is due to lack of metabolic reward. However, after a few days of not wanting sweetness, a little bit of real sugar can reset me to enjoying sugary things. Takes longer to again enjoy an artificial sweetener.

That's not really the same thing, you simply dislike the taste of artificial sweeteners. I dislike Stevia too, I can drink a cup of coffee with it once a day, but if I eat two subsequent things sweetened with stevia I feel like throwing up. Aspartame on the other hand tastes pretty much ok in soft drinks, dunno about other foods.

I think you've misunderstood what they're saying.

I’ve noticed people’s sensory reactions to sweeteners can vary greatly. You can perceive them less or more strongly, they can be sugar-like or weirdly chemical-tasting, etc.

I used to have a very negative reaction to sweeteners in various soda drinks (I remember coke zero tasting so bad, I couldn’t force myself to drink it when I got it for free at a promo). I got used to it over time, now it’s not as repulsive (but nowhere as good as the sugary original either). So it can go both ways, depending on what association your brain and your gut builds over time.

I really want to try allulose sometime, apparently it’s very sugarlike. You can make caramel with it!

Anecdote of 3: I agree, I gave up soda for a couple months and my sense of sweet changed massively. Years drinking soda like water, dipping bread in coke, and supersizing at McD's, all gone because now soda simply tastes much too sweet. Seems like there's some sort of sensory dulling involved.

dipping bread in coke? Is this a thing. I've never heard of it before

I may have been a very extra kid.

Years ago, I started seriously disliking soda because it was far, far too sweet for me. I don't know if soda got sweeter or my taste became more averse to sweet. Since I have a terrible sweet tooth and eat too much candy[1], I suspect the former.

In any case, I stopped drinking soda entirely because it was too unpleasant. Then I discovered how easy it is to make my own and started doing that. That way, I can make it to my preferred sweetness level.

[1] I realize that soda is literally candy, but it's too sweet for me anyway. I've never understood why it's different than, say, a hard candy that is 98% sugar.

A nutritionist I spoke to said that if you have to consume sugar, it's better to eat it than drink it since eating can at least make you feel full (esp. if the sugar comes in the form of something like a pastry which has extra non-sugar carbs contributing to your fullness).

When my wife and I went to Italy on our honeymoon, and subsequently decided to use carbonated water as a way of dropping our coke addictions, the next few months felt like I was a drug fiend breaking an addiction.

Vegetables tasted so good. Vanilla added to our Starbucks coffee started to taste awful. It felt like a world of taste opening up. Food started to satisfy so much more. It was easier to identify when I was full and avoid overeating.

The sugar industry has so evil and has done so much damage to this country and to the world.

In my experience, it's the residual sugar (in everything that comes in a box/wrapper/bag) that keeps this "sweetness sensitivity" high.

I've done strict keto off and on for 10+ years and drank Diet Coke like it was going off the market. When I cut out carbs (we're talking < 30g per day), it becomes obvious that it's real sugar that triggers the cravings for me. Never did a diet soda make me crave a candy bar. Instead, it was generally something like a bite of a real hamburger bun, or a couple french fries.

It's really hard to isolate the effects of things like artificial sweeteners when "real" sugar is absolutely everywhere.