From the Litlvan Forum:

How to refuse cookies? Or at least sweet?

The main thing is not to give up. There is another effective method - you have to scare yourself.
I will tell you about myself: my mother has diabetes, that is, it can be inherited. I was scared and decided to stop eating sugar.
At that time, I was working in a stall and a new horse came to us, brought from some village, and they were not sucked with sugar there. And I naïve decided to give the horse a piece of sugar. The horse took the sugar, spit and spit right in my eye, and then realized that sugar is evil.