It's much harder to get the same amount of sugar from actual fruit, as fruit juice is pretty much extracting the sugar and water from the fruit. That is, a glass of orange juice takes more than one orange. The part of the fruit that is thrown out when juicing is also good for you: fiber.
What do you mean by adjust? Is there some withdrawal period from a product like Pepsi? Or adjust to the dissatisfying taste of water compared to sugary drinks?
Sugar is the best and fastest source of energy found in the nature. We are programmed to like it and remember when we ingest it, and that behavior is rewarded by feeling good.
A lack of that feeling will make you feel less good. Experts say it takes up to a month for that imbalance to normalize.
Caffeine withdrawal can give you much more than headaches, and withdrawal can last for at least a week, though generally at higher dosages.
Until I realised what was going on, when I was taking breaks from using 360mg very other day - so equivalent to 5-6 cups of coffee - to boost my weight lifting in periods, I had week long bouts of diarrhoea, intense headaches, shakes setting in in the evening (so severe I had to time my painkillers, or I'd have problems swallowing them because I had difficulty holding my hands steady enough to drink a glass of water), fever, and night sweats.
Caffeine can be a nasty drug to go cold turkey from if your intake has been high. Best bet is to step down gradually (not a long period - over a week or two), coupled with pre-emptively taking paracetamol/acetaminophen in the early evening.
Often, someone who gets a lot of caffeine and starts experiencing symptoms like above may be experiencing withdrawal without being aware.
The calorie contents of Pepsi is not that far removed from many fruit juice products. Some, like lemonades, can often be higher in sugars than Pepsi.