The process of digestion involves a series of functions conducted by the digestive organs, which include your mouth, esophagus, stomach, intestines, rectum and anus. The digestive process begins when edibles enter your mouth, and it ends as excrement from your anus 1. Your stomach and small intestine play the biggest role in metabolizing nutrients, including the breakdown and distribution of caffeine and protein to other parts of your body for further use.

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Digestive Role of Stomach and Small Intestine

The digestion of any food or beverage involves passage from your stomach to the small intestine. The stomach serves as the catch-all that dilutes entering contents with digestive juices. Caffeine has a smaller chemical structure, making it pass rather quickly from your stomach, but protein requires a lengthy amount of time for digestive juices to dilute it before moving into the small intestine. Inside your small intestine, digestive juices produced from your pancreas and liver mix with the contents to break them down into the smallest possible molecules. Pancreatic juices contain the majority of enzymes responsible for breaking proteins down.

Caffeine Digestion

The moment you swallow a caffeine-containing food, it rushes through your stomach, but during passage, it increases the acidic juices produced before moving into your small intestine. If you have other food contents sitting in your stomach during caffeine's passage, your stomach may prematurely empty these items into the small intestine before full dilution occurs, resulting in abdominal distress. In the small intestine, caffeine absorbs into the lining, then enters your bloodstream, where it travels to the receptors of a calming chemical called adenosine in your brain. Caffeine blocks this chemical, resulting in the opposing response of excitement or alertness. Caffeine digestion takes as little as 15 minutes, but it takes up to six hours for only half of the caffeine absorbed to be eliminated.

Protein Digestion

Protein-containing foods consist of large molecules that must be broken down by digestive enzymes before the nutrients can be used by other parts of your body. In your stomach, protein is met by a gastric juice called pepsin, which allows the protein to smoothly transition into the small intestine. The pancreatic enzymes break the protein down into the smallest amino acids possible, which are then absorbed into the bloodstream and carried to various organs and cells of the body.

Nutritive Value of Caffeine and Protein

Caffeine comes in foods and beverages such as chocolate, sodas and coffee, and in some medications 1. It is a central nervous system stimulant that temporarily increases your heart rate, opens your air passages, delays fatigue and allows muscles to contract easily. Caffeine has many positive uses when taken in moderation -- 200 mg or less per day -- but it has no nutritive value in the digestive process. Conversely, protein is significant to your overall health, and your body requires this nutrient to repair muscle, maintain brain cells and store caloric energy. Consumption of too much protein, especially from high fat sources, can increase your risk of organ damage, so daily intake is recommended at no more than 35 percent of your total food calories. Lean sources include baked chicken, fish and low-fat dairy.