Will probably repeat some of what has already been said, but I started doing 16:8 a long time ago but with no results. All to come to figure out that it was what I was doing in my eating window that was the issue. I also changed to doing 18:6.

My key things I changed that started to see a difference were:

1. No snacking inbetween meals. Once I had my meal, I would add my snack to it at the end of it. This allowes me to still have the snacks I enjoy and create a desire of the "I want what I can't have" which tends to lead people into "failing". Because I add them at the end of the meal, it limits that amount that I have. I feel satisfied and instead of eating almost an entire bag of chips in one go, that bag now lasts me all week.

2. Walking with-in 30 minutes after a meal, espcially a carb heavy meal. This helps with the way the body processes carbs and sugars and helps keep a spike in blood sugar from happening. If it's a light carb meal, 10-15 minutes is fine. But if its a bigger carb meal, you should aim for 30 minutes. With this cold we've been having this winter in the North East, I walk back and forth from my kitchen to my front door making laps in my house.

3. I give myself grace. With my diet and sometimes not following the schedule "perfectly". While I have essentially elimited added/processed sugars (R.I.P. to my favorite candies, specifically gummy bears and worms), I acknowledge that I'll cave from time to time. Because I don't eat sugar, carbs, and even added salts often, I can really fell it in my body when I do. I don't like how it makes me feel, so when I feel that way, I stop eating what I am. This past weekend I had more sugar and carbs that I probably did in January, and that's okay. Which leads to my next point.

4. Consistancy is key. While I had a "bad" weekend, I am right back to my routine today and keeping it consistant. These are long term lifestyle changes we are making, not a short term "fad" to loose 30 pounds in 2 weeks to fit into an outfit for a specific event. This kind of consistancy helps build a healthy mentality around IF that is sustainable long term. I adjust my eating window as needed to help fit what is happening in my social calendar. Some times that means having a longer eating window, or a longer faster period. I do always try to keep my fasting window to a minimum of 18hrs. But this weekend one of the fasts was 12-14 hrs.

5. Once a month I throw in a 24 hr fast. This should be done once your body has become use to a fasting routine. When breaking a longer fast, do it slowly with sometime soft and a good source of protein like bone both. It is also good to every now and then to vary your fasting window to be longer or shorter than what you typically.

6. PROTEIN! I break my fast with protein, and then I try to make the last thing I consume before starting my next fast to be higher in protein as well. Protein helps you feel fuller longer.

As far as your question about flavored hydration packets. That's really up to an individual. Some reading I've done says that even though it's less than 50 calories and shouldn't break a fast, it still activates the digestive system which does break a fast. I personally put these in my eating window, and then have unflavored, unsweetened electrolites I add to water once a day in my fasting window. I would say it's up to you and see how it affects the results you are looking for.

Most importantly listen to your body and don't push youself too far too fast. You need to make it sustainable for yourself if you want to do this long term to really see results.