There are a lot of conflicting studies, many of which have their own flaws. As far as I can tell, we don't have any fully accepted theories. The best I could find was a phenomena known as compensation, where people are "ingesting calories later to compensate for energy deficit caused by [artificial sweeteners]". Basically, you trick your body into thinking it's going to get a lot of sugar, and then you don't give it any, so it sends messages to your brain that it's still hungry for sugar, leading you to eat more than you would have if you drank a soda.

The study

"Contribute to obesity" and "bad for you" are not necessarily the same thing. Which one are you asking about?

Some sugar substitutes are bad for you for reasons unrelated to weight gain, such as messing up your gut microbiome.

There is some evidence, although it's not conclusive, that sugar substitutes may be linked to weight gain. The idea is that your body associated the sweet taste with an increase in blood sugar and thus expects an increase in blood sugar. When you drink a sugar free drink, you get the taste but don't get the blood sugar increase, so your body makes you crave sugar to get that increase it was expecting, and you end up consuming more calories than you otherwise would have.

The hard science tells us these artificial sweeteners contain 0 calories, and 0 anything else. It's purely taste and no harm of any sort. That's the hard truth. They are 0 calories sweeteners, and there are no hidden calories in them. You'd die trying to survive off 0 calorie foods. There is no disputing that.

With the hard science out of the way comes the dilemma of separating bad data humans provide, with any sort of response from the human body. We can obviously taste sugar. There's a chance our bodies respond the sweet taste some way. Maybe the taste makes us more hungry. In evolutionary terms it's not the most stupid idea if you think about hunter-gatherers a few hundred thousand years ago.

But that is speculation only. It's possible that it's all bad data and that artificial sweeteners do nothing at all. We just don't know. We need more data on the subject.

Your question can't be answered. We don't know. It's an ongoing point of research.

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Not the best answer but I read before the brain gets used to releasing hormones based on sweet flavor not by waiting to figure out what it actually is.

So based on what the brain is used to it'll still release the same enzymes and hormones yet not have the proper sugars to bind with, etc.

Hi!

There are lots of issues.

It depends on what specific sweetener you are referring to, and what you mean by "bad for us" or "contribute to obesity"

• As far as bad for us - sucralose can be a trigger for migraines

The paper Body & brain: No-cal sodas can trick the brain: Sugar-free sweeteners may contribute to obesity risk has lots of details. I'll try to summarize

>saccharin and other sugar-free sweeteners — key weapons in the war on obesity — may paradoxically foster overeating.

This was not a big data study, only 24 subjects.

>One strong link to higher diet soda consumption was reduced activation of the caudate head, an area associated with the food motivation and reward system. Green and Murphy note that decreased activation of this brain region has also been linked to higher risk of obesity.

It finds a link (but not proven causality) that the area of the brain lit up (fMRI studies) in response to diet soda was the same area that is associated with obesity.

in earlier studies

> Swithers’ group showed that rats that always received a saccha- rin-sweetened yogurt learned to modu- late their food intake to account for the sweetener’s failure to deliver calories. But rats that alternately got saccharin- and sugar-sweetened yogurts got fat.

If you are curious about the research, Bisphenol-A, found in BPA plastics has been linked to obesity. Childhood exposure causes people to want more sweet foods.

“bad for you” and weight gain are not the same. you can be bone skinny and still have health problems from your diet

Maybe some of the sugar substitutes compete with the sites on enzymes responsible for giving us energy which normally attach sugar. This causes an acute sense of sugar deficit and a deep sugar hunger. (?)