What is protein and how is it digested?<\/h4>\n
Protein<\/span>s are<\/span>\u00a0<\/span>essential components of the human body<\/span>\u00a0\u2013<\/span>\u00a0our<\/span>\u00a0<\/span>muscle, skin, hair<\/span>, hormones,\u00a0<\/span>and\u00a0<\/span>enzymes<\/span>, for example,<\/span>\u00a0<\/span>are<\/span>\u00a0made from protein<\/span>.\u00a0<\/span>Proteins<\/span>\u00a0<\/span>are polymers<\/span>\u00a0(polypeptides)\u00a0<\/span>made up of<\/span>\u00a0sequences<\/span>\/chains of<\/span>\u00a0<\/span>small organic compounds called\u00a0<\/span>amino acids<\/span>.\u00a0<\/span>A chain of\u00a0<\/span>less than 30 amino acids is referred to as a peptide.\u00a0<\/span>T<\/span>h<\/span>ere are 20<\/span>\u00a0amino acids that form the building blocks for proteins, but t<\/span>he body\u00a0<\/span>can\u00a0<\/span>only\u00a0<\/span>make 11 of\u00a0<\/span>the<\/span>se<\/span>\u00a0<\/span>\u2013<\/span>\u00a0the<\/span>\u00a0<\/span>other\u00a0<\/span>nine<\/span>, known as essential amino acids, must come from the diet.\u00a0<\/span>\u00a0<\/span><\/p>\n![\"\"](\"https:\/\/dev.livaux.com\/wp-content\/uploads\/2022\/11\/Chart1.png\")
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\u00a0<\/span><\/p>\nProtein is one of the three macronutrients in our diet, the other two being carbohydrate and fat.\u00a0<\/span>Dietary s<\/span>ources of protein include meat<\/span>, dairy, fish, eggs, legumes,\u00a0<\/span>nuts<\/span>\u00a0and grains.\u00a0<\/span>\u00a0<\/span><\/p>\nThe digestion of dietary proteins in humans begins in the stomach where the initial breakdown is done via the action of pepsin (a protease) and hydrochloric acid<\/span>\u00a0(stomach acid)<\/span>. The resulting peptides and protein fragments make their way to the small intestine where further enzymes (<\/span>e.g.<\/span>\u00a0trypsin<\/span>, chymotrypsin<\/span>) continue to digest the peptides and fragments into amino acids and small peptides, which can then be absorbed into the bloodstream.\u00a0<\/span>\u00a0<\/span><\/p>\nOnce absorbed the amino acids and small peptides are\u00a0<\/span>utilised as building blocks by cells in the body to create new proteins, such as enzymes, antibodies, structural proteins (<\/span>e.g.<\/span>\u00a0keratin, collagen and elastin), and messenger proteins (e.g. hormones), or they can be broken down to produce energy.<\/span>\u00a0<\/span><\/p>\nPoor protein digestion<\/h4>\n
Some dietary proteins are more readily digested than others and the presence of a significant amount of poorly digested dietary protein in the stomach can reduce the rate of emptying of the stomach leading to that overfull feeling<\/span>\/bloating.<\/span>\u00a0This is particularly an issue\u00a0<\/span>for<\/span>\u00a0people\u00a0<\/span>with compromised digestion, such as elderly people, who tend to produce less pepsin<\/span>\u00a0and<\/span>\/or<\/span>\u00a0stomach acid<\/span>, or people on proton pump inhibitor drugs, which reduce the production of acid in the stomach.<\/span>\u00a0<\/span>\u00a0<\/span><\/p>\nU<\/span>ndigested protein<\/span>\u00a0and peptides that<\/span>\u00a0<\/span>reach the colon\u00a0<\/span>are<\/span>\u00a0fermented by the gut microbiota.\u00a0<\/span>Fe<\/span>rmentation of protein produces<\/span>\u00a0several\u00a0<\/span>byproducts<\/span>\u00a0including<\/span>\u00a0ammonia<\/span>,\u00a0<\/span>hydrogen sulphide<\/span>,\u00a0<\/span>short chain fatty acids<\/span>\u00a0(SCFA), branched chain fatty acids (BCFA)<\/span>, amines,\u00a0<\/span>phenols<\/span>\u00a0and indoles<\/span>.<\/span>\u00a0Too much protein fermentation<\/span>\u00a0(which can occur with high protein diets or poor digestion of protein)<\/span>\u00a0<\/span>can result in an overabundance of the fermentation\u00a0<\/span>byproducts<\/span>\u00a0<\/span>which may cause inflammation (<\/span>potentially leading to a \"leaky gut\") and excessive proliferation of colonocytes\u00a0<\/span>(potentially leading to colorectal cancer)<\/span>\u00a0<\/span>[1]<\/span>.<\/span>\u00a0Increased fibre fermentation in the colon\u00a0<\/span>with increased SCFA<\/span>\u00a0(especially butyrate)<\/span>\u00a0production\u00a0<\/span>however can\u00a0<\/span>be protective against\u00a0<\/span>colorectal cancer development.\u00a0<\/span>\u00a0<\/span>\u00a0<\/span><\/p>\n![\"\"](\"https:\/\/dev.livaux.com\/wp-content\/uploads\/2022\/11\/Chart2.png\")
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\u00a0<\/span><\/p>\nProtein intolerance\/sensitivity<\/h4>\n
Some people\u00a0<\/span>are also intolerant\u00a0<\/span>or sensitive\u00a0<\/span>to\u00a0<\/span>certain\u00a0<\/span>proteins.\u00a0<\/span>The most\u00a0<\/span>well-known<\/span>\u00a0is gluten intolerance<\/span>\/sensitivity<\/span>, but\u00a0<\/span>casein\u00a0<\/span>may<\/span>\u00a0also pose an issue for some.\u00a0<\/span>\u00a0<\/span><\/p>\nCasein intolerance<\/h4>\n
Casein is\u00a0<\/span>the<\/span>\u00a0major milk protein.\u00a0<\/span>Research suggests t<\/span>he A1 type of beta\u00a0<\/span>may<\/span>\u00a0<\/span>cause intolerance reactions<\/span>\u00a0[2<\/span>,3]<\/span>.<\/span>\u00a0In contrast, the A2\u00a0<\/span>type and whey (the\u00a0<\/span>minor milk protein) have not been associated with\u00a0<\/span>reactions and appear to be well-tolerated<\/span>\u00a0<\/span>[4,5]<\/span>.<\/span>\u00a0<\/span>\u00a0<\/span>\u00a0<\/span><\/p>\nWhen casein is digested,\u00a0<\/span>an opiate-like substance,\u00a0<\/span>beta-casomorphin-7<\/span>, is released.\u00a0<\/span>It is thought that this compound is responsible for the intolerance reactions\u00a0<\/span>observed with casein\u00a0<\/span>by stimulating histamine release<\/span>\u00a0<\/span>[3]<\/span>.\u00a0<\/span>Histamine is involved in the inflammatory response to allergens.\u00a0<\/span>\u00a0<\/span><\/p>\nGluten<\/span>\u00a0Intolerance<\/span>\u00a0<\/span><\/h4>\nMany people experience digestive<\/span>\u00a0and other health problems when they eat gluten\/wheat.\u00a0<\/span>Gluten is\u00a0<\/span>a<\/span>\u00a0group of<\/span>\u00a0protein<\/span>s<\/span>\u00a0found in wheat,\u00a0<\/span>barley<\/span>\u00a0and rye<\/span>.<\/span>\u00a0Wheat is\u00a0<\/span>used as an ingredient in\u00a0<\/span>a large number of<\/span>\u00a0foods, including\u00a0<\/span>breads, pastas<\/span>,\u00a0<\/span>cereals<\/span>, biscuits, crackers, cakes and pastries<\/span>, but it also shows up in\u00a0<\/span>a lot of convenience foods, like soups, sauces, spices<\/span>,<\/span>\u00a0drinks, processed meats and ready-made meals.\u00a0<\/span>