What is the general term used to describe a group of diseases in which intestinal uptake of nutrients is impaired?

The term used for the condition, in which the uptake of nutrients from the small intestine is impaired is malabsorption.

The malabsorption is a condition, in which the small intestine walls become unable to uptake the nutrients in the blood. This condition can be caused by many different reasons, which affect the wall of the intestine. These conditions include infections, trauma, celiac disease, and surgery. Some diseases such as Crohn's disease, pancreatitis (chronic), or cystic fibrosis is also responsible for the malabsorption.

yes, because even though a theory has a  lot of evidence to support it, it is not always true