Which nutrient is primarily broken down in the stomach?

The stomach primarily breaks down proteins through a process involving gastric juices, which contain hydrochloric acid and the enzyme pepsin. These substances work together to denature proteins, unraveling their complex structures and making them more accessible for further digestion. Pepsin specifically targets peptide bonds in proteins, facilitating their breakdown into smaller peptides.

While some digestion of carbohydrates and fats does occur in the stomach, it is not the primary function of this organ. Carbohydrate digestion mainly starts in the mouth with salivary amylase, and fat digestion largely occurs in the small intestine with the help of bile and pancreatic lipase. Vitamins do not undergo significant breakdown in the stomach; they are absorbed mostly in the intestines. This distinction emphasizes the critical role of the stomach in protein digestion, making it clear why this nutrient is primarily processed there.