When I was growing up, my mom noticed my sister and I reacted poorly to artificial sweeteners and colors; this was the single best thing she ever did, in addition to stripping our diets to avoid those particular things. Consequently, we grew up not eating a lot of high-fructose corn syrup, saccharine, phenylalanine, or any of those red/yellow dye thingies. By reacting poorly, I mean to say that my sister would run in circles until she fell down and I would get mean, grouchy, and depressed to an extreme rather uncommon to a 5 year old female child. Because most sugary foods also contained some other unnatural ingredient, we didn't eat a lot of sugary foods either.... at least not until I was in my late teens...
After 4 long years of unhappiness, mood swings, angry depression, sinus problems, and general gastrointestinal discomfort, a friend who studied eastern medicine recommended I go on a candida diet. This means stripping sugars and fast-burning carbs to avoid exacerbating the normal yeast humans have in their gastrointestinal system. I played with this diet, and ultimately 'failed' at it for years. But I learned a lot about how food can produce adverse reactions to your system, and not all are noticeable within the same day of consumption -- and that's the big part...
If you truly want to experiment on yourself to know how you react to a diet or to a particular item of food, you need to monitor over at least 4 days after 'exposure.' The effects of excessive sugar-eating for one day can result in up to 3 days of withdrawal, culminating in severe moodiness on the 2nd and 3rd day. AND these are not simple cranky moods... these are fits of mood and depression that I've seen other people also do on a regular basis, and that can go on for days and weeks -- imagine if they had the presence of mind to know that it was all a reaction their body was having to something they ate a couple days ago.
So, how do I avoid sugar? I don't eat packaged foods! Read all ingredients labels! I avoid caffeine and alcohol, which disrupt the body's pH. I eat hardy, whole-grain breads with no added sugars if I eat bread at all, and less ripened fruits and vegetables with less natural sugar: berries, mangoes, avocados, zucchini, eggplant, greener bananas, red/purple potatoes, yams. I also need to (and am diversifying my diet enough to allow it) eat more raw veggies and nut-based meals with some good probiotics that will keep the yeast at bay.