Protein is an essential nutrient found in muscle, bone, and other tissues. When you eat it, your digestive system breaks it down into individual amino acids. Protein digestion time is determined by the metabolic process that occurs in each individuals gastrointestinal tract, among other factors.
Protein metabolism takes time due to the chemical breakdown process that is required in the stomach and small intestine. Based on the type of protein consumed, your body could digest as little as 3g or as much as 10g per hour.
Protein Digestion Process
Protein digestion begins in the mouth, where chewing breaks the food down into smaller pieces. From there, the food enters the stomach, where gastric juices, containing hydrochloric acid and pepsin, break down the protein even further.
Stomach contractions churn the partially-digested protein into a mixture called chyme. The digestion of protein takes a longer time in the stomach, as compared to carbohydrates, but a shorter time as compared to fat.
Chyme enters the small intestine from the stomach, where majority of protein digestion occurs. Enzymes released by the pancreas, called chymotrypsin and trypsin, continue the digestion process.
Additional enzymes, from the cells that line the small intestine, break apart protein into individual amino acids. The muscles that contract in the small intestine mix and propel the digested proteins to the absorption sites. Very little protein will make it to the large intestine, as long as you are not consuming excessive amounts.
Read more: What Helps Absorb Protein?
Factors that Impact Protein Metabolism
Although the digestion process of protein occurs in the same way, there are multiple factors that can affect the protein digestion time. One of those factors is the composition of the consumed protein.
The simplest forms of protein are strings of amino acids held together by peptide bonds. Foods that we consume contain proteins in their most complex form, where the strings of amino acids within the protein are raveled up. They need to be unraveled, and broken apart, in order for the intestines to absorb the individual amino acids and transfer them into the bloodstream.
The acids within the stomach help to unfold all of the raveled amino acid chains, allowing digestive enzymes produced by the stomach's wall to work on breaking the peptide bonds apart. The easier it is to reach the amino acids, the quicker the protein can be processed.
Therefore, protein with a composition that is less-complex has quicker digestive rates. Whey protein, found in milk, is an example of a quick-digesting protein. Its absorption rate has been estimated at approximately 10 grams per hour, compared to a cooked egg that has an absorption rate of approximately 3 grams per hour, according to the Journal of the International Society of Sports Nutrition.
Eating Enough Protein
In order to properly utilize protein, it's important to ensure that you're consuming enough daily. The Recommended Dietary Allowance is 0.8 grams of good-quality protein, per kilogram of body weight, per day. An upper range is set to consume no more than 35% of your total energy intake from protein. This is set to decrease risk of chronic diseases.
In a June, 2014 study published in The Journal of Nutrition, researchers found that evenly-distributing protein consumption throughout the day resulted in about a 25% increase in muscle protein synthesis over 24 hours. Muscle synthesis is essential for the body to grow, maintain, and repair its skeletal muscle groups. This shows that eating large amounts of protein in one sitting is not the ideal way to get your recommended daily amount of protein.
Read more: 4 Signs You May Be Eating Too Much Protein
- Journal of Nutrition: "Dietary Protein Distribution Positively Influences 24-Hour Muscle Protein Synthesis in Healthy Adults"
- Medical LibreTexts: "Protein Digestion, Absorption and Metabolism"
- Journal of the International Society of Sports Nutrition: "How much protein can the body use in a single meal for muscle-building? Implications for daily protein distribution"
- Dairy Protein Digestion: "Life in the Slow Lane"
- Institute of Medicine: "Dietary Reference Intakes"