Fiber-rich foods are capable of helping you block fat absorption. You can find fiber in plants. We eat fiber and consume it through vegetables, fruits, and grains. It is great for weight loss and can help slow down your overall fat absorption from the foods that we eat. Essentially we are teaching our body to consume fewer calories when we eat more fiber.
Despite that a diet rich in fiber is going to have some results, and you are able to benefit from it in the long-term (especially your health) it is not going to be enough to block fat absorption on its own.
This means that you are going to need something extra if you want to truly lose weight. This is why just having fiber in your fat blocker pills is not going to be enough.