I believe that it is not just "sugar" that you can be influenced by, but by carbohydrates in general. When I begin a lower-carb regimine, there's always a 7-10 day adjustment period as my body begins to switch from getting its fuel from glucose from carbs (starches and sugars I was eating) to ketones from the higher fat I'm eating now. It's sometimes called the "Atkins flu" or "Ketogenic flu". Lethargy, slight achiness, melancholy... but it eases completely away after a week or so.

That being said, the best way to avoid ANY of those sorts of reactions, whether from caffeine withdrawal to carb withdrawal, is to ease into any sort of strict restriction over a few weeks. In fact, I was reading an article the other day that suggested that easing into lower carb eating made the lifestyle easier to maintain than if you dive into it all at once. You can always go MORE restrictive once you have lessened a particular type of food, but if you give up at the beginning because it's just too much change for your body at once, then you'll never get the benefits of the plan.

I am not confusing energy drinks with coffee. (Did I mention I once upon a time, before I discovered tea, drank coffee? I guess not, but I only started drinking tea like 2 years ago...)

The substance causing my elevated heart rate, higher blood pressure, water retention, migraines and insomnia was caffeine, not sugar.

And as long as you don't have one of the above symptoms, you may drink all the coffee your heart desires (who am I to tell anyone to quit drinking coffee anyway?). BUT, if you do experience those problems, it's worth taking a look on your daily intake of caffeine. It's just that, if someone shows all the health benefits of caffeine, I'd also like to point out it's not all glory. Obviously, caffeine, in the right dosage, causes a lot of good things and I think once we truly start to look into the benefits of caffeine, we'll find even more goodies!

Besides that, I actually need to take a form of daily medication that, in combination with any higher amount of caffeine can cause heart palpitations. I no longer have any excuse now to not take my meds.

To the OP - I would suggest some food journaling while you are going through your trial and error process. I don't mean just writing what you eat, but writing how you feel about it. Basically - when I read what you wrote, to me because I'm looking at it from the outside, it's pretty easy to see what you can do. So, write those things down and then read back over them. But do it looking at it like you are a scientist trying to figure out how his experiment went wrong. (Come here and post of course, too!) Not necessarily every day (I know I could never keep to that) but when you are having a good day or a bad day write out why you think it is. Then go back to that and study it for patterns.

Another thought on the sugar topic - I get blood sugar swings when I eat white flour or just plain sugary junk foods. It makes me crabby, HUNGRY, mentally cloudy and just plain uncomfortable. It sets my day up for poor food choices (choices driven by low blood sugar and not by self care). I've learned that if I decide I want one of those foods, I can avoid that feeling by eating protein with it and keeping the portion in check. Instead of a 10 pack of Timbits, if I eat one full size donut (or even half a donut) along with some cottage cheese or unsweetened greek yogurt or some eggs or whatever, it helps. BTW - This is a perfect example of a trial and error journal result for me.

And yeah - don't feel like you have to change everything at once. It's not about perfection. It's about learning to eat and enjoy foods in a way that nourishes your body and mind. There's no finish line. It's just a life process of learning what works and what doesn't. As long as you're moving forward, you'll be feeling better and better. My $0.02 is there is no such thing as goal. Yeah, I want to lose 20 or 30lbs but it's not like anything is going to change for me when I do. It's still me plugging along taking care of myself and still figuring it out through trial and error because life is constantly changing.

I can chime in on caffeine withdrawals being a very (VERY) real thing. I tried to quit caffeine a few years ago and it didn't go well. I was nauseous with crippling headaches and irritability. So I did what people here have mentioned, I starting tapering off the soda (even diet) and did have to sub in a lot of aspirin for the head but finally kicked the soda. I have yet to kick coffee but I love it so much I don't think I ever will.

Moderation is the key to lasting change, if you change too much at once you'll be miserable and more apt to fall back, I think.

Different things work for different people. The main thing is to be healthy about it. I used slim-fast. I lost a lot of weight and then it stopped all of a sudden. I had developed a thyroid disease, and gall stones and all kinds of other problems from doing it the wrong way.

I think a lot of us underestimate how intestinal gut flora plays a role in even minor dietary changes. We have a certain established gut flora and they demand their food too. When we make rapid or drastic changes, they react.

Slow changes are definitely better for the body, but also best for the intestinal gut flora, as it allows the gut to "reconfigure" in a safer way.