Sentences of a paragraph are given below in jumbled order. Arrange the sentences in the right order to form a meaningful and coherent paragraph.

P. Its role in human nutrition was not fully known.

Q. This has resulted in a better appreciation of the role of fibrous food in human health.

R. Later research has thrown light on many other ingredients that are digested by man and have more fibres.

S. In early days, people only knew that this fibre prevented constipation.