The phrase "to extract the nutrients" means to take out or remove the important elements found in food or other substances that our body needs for growth, energy, and good health. Full definition
These bugs help the digestive tract function properly, which in turn enhances your body's ability to extract nutrients from food. (beginwithinnutrition.com)
If they can't chew their food properly, they can't extract the nutrients they need from the food. (second-opinion-doc.com)
A cat food can therefore be labeled nutritionally complete even if the cat's digestive system can not extract those nutrients. (petpeoplesplace.com)