Which type of substance does NOT need to be broken down into smaller units before absorption?

Vitamins are unique compared to fats, carbohydrates, and proteins because they do not require digestion or breakdown into smaller units for absorption in the body. Vitamins are categorized into two types: water-soluble and fat-soluble. Water-soluble vitamins, such as vitamin C and the B vitamins, can be absorbed directly into the bloodstream through the intestinal lining as they are, without needing to be broken down. Fat-soluble vitamins, such as A, D, E, and K, are absorbed along with dietary fats but do not need to be broken down into smaller components prior to absorption.

In contrast, fats must undergo emulsification and enzymatic digestion to break them down into fatty acids and monoglycerides before they can be absorbed. Carbohydrates require enzymatic breakdown into simpler sugars, like glucose, for absorption as well. Proteins must be digested into amino acids through the action of enzymes before absorption can occur. Thus, vitamins stand apart in that they are readily absorbed in their intact forms.