Roughage, in simplest terms, is any part of flower, vegetables or grains that we cannot digest. It is also known as dietary fiber. Some examples of roughage are oats, lignin, cellulose, etc. Common sources of roughage in our diet include fruits, grains, nuts, beans, etc. Roughage has several health benefits, even though it does not provide any nourishment. The most significant function of roughage is to help our digestive system and prevent and relieve constipation. The insoluble part of roughage absorbs water and swells to form a gel and keeps the bowel movement soft and thus easy to pass. The soluble portion of the roughage also helps to remove cholesterol from our body and maintains the blood sugar level (by slowing down its absorption in our blood). Roughage also adds bulk to our diet and makes us feel full, thus helping in the weight management.
Lack of roughage in our diet will, thus, result in constipation and increased blood sugar level, cholesterol levels and may also cause weight gain. Hence, one should eat roughage as a fixed constituent of the diet.
Hope this helps.