For some people, their digestive tract cannot absorb vitamin D well.

As a result, their digestive tracts can't absorb certain nutrients properly, possibly leading to B12 deficiency and iron-deficiency anemia.

If the measurements are extended globally, the world's remaining tracts of tropical rain forests could be absorbing a billion tons of carbon dioxide every year, one-sixth of the amount produced by burning fuels, said Pieter Tans of the National Oceanic and Atmospheric Administration.

A member of the cestode class, tapeworms do not have digestive tracts to absorb nutrients, instead their surface body layer is metabolically active with nutrients and waste passing in and out continuously.

Dietary fiber helps the gastrointestinal tract absorb excess water and remove food wastes, but an excessively high intake of dietary fiber will also negatively affect the absorption process in the intestinal tract.

Your digestive tract cannot adequately absorb vitamin D. Certain medical problems, including Crohn's disease, cystic fibrosis, and celiac disease, can affect your intestine's ability to absorb vitamin D from the food you eat.

In the later stages of HIV infection, diarrhea is thought to be a reflection of changes in the way the intestinal tract absorbs nutrients, and may be an important component of HIV-related wasting.

Post-operative gastric bypass patients develop a lowered tolerance for alcoholic beverages because their altered digestive tract absorbs alcohol at a faster rate than people who have not undergone the surgery.

The immature gastrointestinal tracts of infants and small children can also absorb drugs faster, which would make a small dose proportionately larger and increase its toxic effects as well.

They have no mouth or digestive tract, and like parasitic worms, absorb nutrients produced by the bacteria in their tissues.