Barring any medical conditions that are aggravated by eating lots of fiber, most people would probably find that it's a silver bullet for reducing sugar cravings, becoming healthier, and, yes, losing weight.
Food journals are useful for tracking your eating patterns, just like you would track your spending. But at the end of the day, the result is the same surprise at how much you are eating ~ or spending.
But if you're focusing on fiber, all you need is to add. Basically you're just counting up the fiber grams, veritable deposits in your physical health account.
You can Google the fiber grams for various fruits, vegetables and nuts, but to simplify it for you, a 1/2 cup serving for most of them contains about 3 - 4 grams.
But if you set a goal to eat 35 to 40 grams of fiber every day, you really have to eat plenty of good stuff to reach that amount. You can't eat junk because there's little fiber in processed foods. Not only that, you WON"T eat junk if you're lasered in on getting enough fiber because you won't have enough room in your tummy!
What's not to like about that approach?