Sugar isn't strictly bad for us. The body uses sugar for a lot of important things like being the primary source of energy in the body. Too much of anything is bad and we just tend to have too much sugar. When we have too much sugar it throws our body out of balance and can even lead to the body not producing the natural sugars that it needs.

Cravings are the body's way of telling us we need something. When you're dehydrated you crave water because you need it. Sugar is one of the main ways we get energy so the brain sends out reward signals when we ingest sugar because it wants to keep getting high-energy foods. In nature, it's difficult to get energy-dense foods like that so it wants us to keep eating more. The problem is, with modern society we've made it too easy to get processed sugar. Ultimately, it's just too much of a good thing.

Evolution is a slow process. Your body doesn't know that it's not a hunter-gatherer barely managing to survive by hunting the woolly mammoth. Your body thinks it desperately needs every calorie it can get if you're going to build up enough fat to survive the harsh winter, and it knows sweet things are rich in calories.

Sugar itself isn't bad for you, TOO MUCH sugar is bad for you.

For like 99.99999% of our evolutionary history, food was scarce and unpredictable. It was practically impossible to find enough calories to eat too much. Therefore, having the trait "whenever you encounter an energy-rich food source, eat as much as you can and turn any excess energy consumed into fat" was a GOOD thing. Any animals that had this trait, including our ancestors, had a survival advantage! If you craved to eat as much high-energy food as you could find, you were more likely to survive a famine, drought, injury, or illness.

On the time scale that evolution creates changes, food becoming cheap and plentiful in the modern age happened extremely recently. It's only been like ~150 years that regular non-rich people could afford enough food that it's easily possible to eat too much. To evolution, that's essentially nothing. That's a single-digit number of generations! Human evolution takes tens of thousands of years or more to produce changes.

So that's the problem: We're all still running a program in our brains that says "eat as much sugar as you can find" because that strategy gave our ancestors a survival advantage for like a billion years, and now it's backfiring for the last hundred years or so and there hasn't been time to change the program yet.

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As I was explained by gastroenterologist - when you eat sugar it creates micro flora that it return makes you want to eat even more sugar, so it’s a vicious circle)))

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