“You have to eat a lot of fiber when you're constipated.”
You find out that your son hasn't pooped in 3 days. You tell him what he should do to fix it.
You have to eat a lot of fiber when you're constipated.
This is a very straightforward way to give someone advice. You use this phrase when you definitely know more about something than the people who are listening:
A: I've never eaten that before. Do you eat it raw?
B: No, you have to cook it.
You can also use "You have to ___" when you're excited about something and you want to share it:
You have to try this! It's delicious!
If you use "You have to ___" to share an opinion, you might come across as rude. For example, don't use this phrase when giving friends advice about their relationships, job, etc.
"Fiber" is something that's contained in certain foods. It's a part of a plant that your body can't digest. Some foods that contain fiber include:
Fiber is supposed to be good for you because it keeps your digestion regular. In other words, when you eat plenty of fiber, you use the bathroom at normal times each day.
When you're talking about food, you can say that something "has fiber":
Beans have a lot of fiber.
When someone has trouble with making bowel movements (pooping), they are "constipated". When you're constipated, you don't poop as often as usual.
"Constipated" is an adjective:
The noun form of "constipated" is "constipation":
One of the side effects of the medicine she takes is constipation.
We use this word when talking to a doctor or nurse, and also when talking about this condition in regular conversation.