Where is food absorbed

Food is mainly absorbed in the small intestine of the human body, while small amounts of nutrients are absorbed in the stomach and large intestine. The process of nutrient absorption involves mechanical digestion in the oral cavity, breakdown of gastric acid, enzymatic hydrolysis in the small intestine, and active transport of villi. Different nutrients have different absorption positions in the digestive tract.

1. Initial Oral Digestion

The oral cavity physically crushes food through chewing, and salivary amylase begins to break down carbohydrates. Although the oral cavity does not directly absorb nutrients, sufficient chewing can improve subsequent digestive efficiency. Some drugs, such as nitroglycerin, can be absorbed into the bloodstream through the sublingual mucosa.

2. Gastric protein processing

The stomach breaks down proteins into peptides through gastric acid and pepsin, while absorbing small amounts of water-soluble substances such as alcohol and some drugs. The endogenous factors secreted by gastric wall cells contribute to the absorption of vitamin B12 in the ileum, but the stomach itself has a weaker function in absorbing nutrients.

3. Small intestine core absorption

About 90% of nutrients are absorbed in the small intestine, the duodenum receives pancreatic juice and bile to help break down fat, the jejunum absorbs most of glucose, amino acids, and water-soluble vitamins, and the ileum focuses on absorbing vitamin B12 and bile salts. The microvilli structure of the small intestine greatly increases the absorption area.

4. Large intestine water recovery

The colon mainly absorbs water and electrolytes, and the gut microbiota ferments unabsorbed dietary fiber here to produce short chain fatty acids. Some minerals such as calcium and magnesium can be absorbed at the end of the colon, but the overall nutrient absorption is less than 10% of the total amount.

5. Special Nutritional Pathway

Medium chain fatty acids can be directly absorbed through the portal vein, iron is mainly absorbed in the duodenum, and fat soluble vitamins such as vitamin K depend on bile emulsification and are absorbed in the jejunum. Some phytochemicals such as quercetin need to be transformed by colonic microbiota before they can be utilized.

It is recommended to chew slowly in daily diet to reduce gastrointestinal burden, and to consume dietary fiber in moderation to maintain intestinal microbiota balance. People with weak digestive function can choose to eat small meals frequently. If there is persistent bloating or diarrhea, their absorption function should be checked in a timely manner. Different cooking methods can affect nutrient absorption, for example, chopping vegetables can increase the bioavailability of carotenoids, and moderate fermentation can enhance mineral absorption.