There are 0 Weight Watchers Points in a plum, but there are 1 Weight Watchers PointsPlus in the same plum. I'll try to explain why this is below.
Weight Watchers count lots of fruit as 0 Points (or free) to encourage people to eat healthy foods. What a lot of people don't realise, however, is that fruit is only "free" up until you consume a certain amount. You can't simply eat fruit all day for 0 points.
The issue with "free" food is that it's confusing for many people. Every food product consists of calories, made up from the amount of protein, carbohydrates, and fats within the food, and therefore no food can actually be free.
To put it as simply as I can, an apple may be considered a "free" food by Weight Watchers, but in fact, an apple contains around 90 calories. So if you ate 10 apples in a day, you'd be consuming 900 calories from just those apples. These are just average figures, but you can obviously see that this isn't sustainable as a "free" food. This leads me onto my next point.
Why does fruit contain PointsPlus in Weight Watchers?
This one's pretty easy to understand. PointsPlus are different to regular Weight Watchers Points because the food items re being used in a recipe, rather than a standalone item. Therefore, the total recipe contains a greater number of products, and you wouldn't see much weight loss (or any) if you were making big recipes out of loads of "free" foods.