I did a no-added-sugar month in March. I wasn't super super diligent about it -- like, I had creamer one day that had 2g of added sugar, I had jam one day, that sort of thing, and I definitely continued to have 1-2 cups of fruit a day and plenty of veggies -- but it was definitely a change, and it definitely illuminated some things for me.
The biggest thing for me was how free I felt from my sugar cravings. I'd had a not-great relationship with sugar for a while (not eating it and then bingeing, basically) and I didn't realize how much headspace I was taking up shaming myself over eating sugar. All of a sudden, when sugar was available and I passed it up... I felt longing sometimes, but also this wide open space that was lack of shame. I was truly amazed at how much time I wasn't spending needling myself for eating a food my ancestors would have screamed at me to eat.
I also noticed that my gut was generally happier. I've usually only noticed an effect on my stomach happiness from acid, but I could tell that my gut was happier at the end of the month than at the start.
I've now been Back On The Cane Juice, but I'm finding that my relationship to the white stuff is much better now. I'm not really feeling cravings; the only time I feel that crave-and-shame spiral are when I'm at, say, a baby shower where there's a crapton of beautiful home-baked pastries. I also find that my gut now can't handle sugar as well; I really notice if I've had a bunch. My boyfriend and I shared a 12 oz milkshake the other day and it definitely made me nauseated. So, whoops on that, though it certainly helps to prevent huge cravings when I imagine how sick I'll feel after eating something. :P
I may do a periodic no-added-sugar month in the future; certainly if I find myself getting into that bad headspace again.
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Re coffee -- I used to be a very regular coffee drinker, 2-3 cups a day. I gave myself acute gastritis by doing this, and then ended up with chronic gastritis when I just.wouldn't.quit. After catching a bad stomach flu which made the gastritis a bit of a nightmare, I just... stopped. I like the taste a lot, but the acid is just too much (even cold brewing a low-acid coffee). I have coffee maybe once a week now, as a Saturday morning pleasure type thing, and often drink decaf when I do.
I do, uh, drink an inordinate amount of tea. Like I go through a few pounds of loose-leaf tea a year. So, I'm definitely not off the caffeine. Still, I find that even two pots of tea doesn't make me jittery in the way that coffee makes me jittery. Something about coffee really zings me, while tea is a much gentler boost.