The vital role of digestion

Digestion is the essential process in the body where food is broken down and the essential nutrients are released and absorbed. A lot can challenge the optimal function of our gut and there are many factors to consider that influence this complex system. Threats to digestion can seriously impair wider health and wellbeing, so supporting robust digestive function is essential. 

Digestion involves the mechanical and chemical breakdown of food, and begins in the mouth. Saliva is produced by glands under the tongue, made mostly of water combined with enzymes, mucous, electrolytes and immune cells, and releases enzymes in response to food.1 The enzyme amylase begins the process of breaking starches down into sugars and lingual lipase, a fat digesting enzyme, is also secreted in the mouth, but it needs the acidic environment of the stomach to be activated.1

The structure of the stomach largely resembles the rest  of  the gastrointestinal (GI)  tract,  but  with  specialised  cells  and  glands  that  secrete  various stomach-specific substances. If it does not function optimally, the rest of the digestive system can become significantly compromised.2 To perform its primary digestive function, parietal  cells  release  hydrochloric acid (HCl)  and  intrinsic  factor  (to  facilitate  absorption  of  vitamin  B12),3  while  the  chief  cells  secrete pepsinogen, which is converted to the active enzyme – pepsin, and gastric lipase, which are responsible for the breakdown of proteins into amino acids and polypeptides, and fats respectively. Stomach acid also acts as an acidic barrier to pathogenic bacteria and in doing so, helps to regulate the abundance and diversity of the intestinal microbiome.4

The bulk of chemical digestion then happens in the duodenum in the small intestine, supported by the secondary digestive organs such as the liver, gall bladder and pancreas, which secrete bile to aid fat digestion and digestive enzymes. In the pancreas, the exocrine epithelial cells called the acini clusters produce bicarbonate, which slightly alkalises the duodenal lumen, pancreatic amylase (for starch), trypsin, chemotrypsin, elastase and carboxypeptidase (for proteins), pancreatic lipase (for fats), ribonuclease and deoxyribonuclease (for nucleic acid). These enzymes are released into the pancreatic duct which joins with the common bile duct to flow into the duodenum.

The intestinal lining also produces an enzyme rich liquid that continues the process of digestion.5 These enzymes are referred to as brush-border enzymes and include: alpha-dextrinase, lactase, sucrase and maltase (for carbohydrates), aminopeptidase, dipeptidase (for proteins), nucleosidase and phosphatase (for nucleotides).

If any of the above steps are compromised, food will be poorly digested which can lead to nutrient deficiencies and chronic symptoms including reflux, bloating and constipation and diarrhea. But poor digestion and absorption can also impede wider health, contributing to obesity, diabetes, autoimmune disorders, hormonal imbalances, chronic fatigue, autism, depression, joint and heart problems.

Convenience Culture, Diets and Allergenic Foods

Fast food options contain higher quantities of trans- and saturated fats, poorer quality protein, refined carbohydrates as well as preservatives, colours, emulsifiers, sweeteners, and flavourings.6 Chronic overproduction of hormones including insulin and glucagon, triggered by a high carbohydrate/refined sugar diet, can have a negative impact on blood sugar and insulin resistance as well as digestive capacity, diverting the body’s attention from the main function of the pancreas to its enzyme-producing role role.7

Certain proteins including gluten, casein (from dairy) and lectins (from grains and pulses) can drive inflammation,8 as these long chain peptides cause increased intestinal permeability if undigested.9 This increases the release of zonulin, increasing intestinal permeability and triggering an inflammatory response. Intestinal permeability is associated with autoimmune conditions,10,11,12 including rheumatoid arthritis,11 Hashimoto’s thyroiditis,13 and multiple sclerosis.14 It can also cause pernicious and iron-deficiency anaemia, by blocking the absorption of nutrients like iron and b12.15

Diets including ketogenic, paleo and low-FODMAP, that restrict certain food groups can further drive inflammation.16,17 These low carbohydrate diets can impact the microbiome due to a lack of prebiotic fibre that feeds the beneficial species.17 Dysbiosis can drive small intestinal bacterial overgrowth,18 exacerbating GERD and IBS-symptoms due to increased methane and hydrogen in the small intestine.19,20

Erratic Eating Patterns

Eating patterns that include frequent snacking, eating on the go, watching the TV or checking phone alerts, puts the body into a sympathetic mode, or fight and flight state. However, the Parasympathetic Nervous System (PNS), also known as the ‘rest and digest’ state, needs to be activated for chemical digestion.21  The PNS is triggered via stimulation of the vagus nerve, which triggers the hypothalamus to instruct the release of acetylcholine and neurotransmitters such as gamma-amino butyric acid (GABA) which exert relaxing, inhibitory effects. 

Chronic Use Of Prescription Medications

Stomach acid acts as an acidic  barrier to pathogenic bacteria and in doing so, helps to regulate the abundance and diversity of the lower intestinal microbiome.25 It also plays  a  part  in  deactivating  environmental  antigens.  If  stomach  acid  production is therefore disrupted by use of the commonly prescribed proton pump  inhibitor  (PPI)  medications  or  antihistamines,  GI  problems like small intestinal bacterial overgrowth PPI (SIBO), 26 IBS 27, 28 or Clostridium difficile-associated diarrhoea25 may occur.  It can also cause reduced nutrient absorption (e.g. iron, 29 B12, 30, 31 vitamin C 32) which, altogether,  may  drive  systemic  issues  like  cardiovascular  disease, 33, 34 dementia 35, 36 and osteoporosis. 37, 38 The surface  mucous  and mucous  neck  cells  secrete  mucus  –  a  viscous  substance  that  protects  the  stomach  lining  from  irritation  and friction. 39 

Decreased mucus secretion caused  by  medications  such  as  non-steroidal  anti-inflammatory drugs (NSAIDS) 40  or  alterations  to  the  thickness  and  viscosity of mucus induced by Helicobacter pylori (H. pylori) infection, 41 can  lead  to  gastritis  or  gastric  ulcers.42 Further, overexpression of related genes including IL-1b polymorphisms, has been associated with a higher risk of gastritis, increased vulnerability to H.pylori infection43 and gastric cancer. 44

• Eat more mindfully - Keep to a regular eating schedule. Before each meal, take a few deep breaths to prepare your body for digestion and avoid distractions (computer/TV/smartphone). Chew your food thoroughly, until mushy.
• Add in digestive enzymes - Taking additional digestive enzymes may significantly improve digestion and absorption of nutrients. Specific enzymes such as protease, lipase, glucoamylase, and lactase can improve the digestion of proteins, fats, carbohydrates, and lactose, respectively. Other enzymes such as cellulase or xylanase can help with fibre-rich foods, reducing their fermentation in the gut.
• Improve bile production - Bile is essential for digestion and absorption of essential fats and fat-soluble vitamins, notably omega-3 and vitamin A, D, E & K. Eat bitter foods before a main meal to stimulate digestive secretions e.g., a simple salad of rocket, watercress and chicory dressed with cold-pressed extra virgin olive oil, apple cider vinegar, and sea salt. Include supplements containing artichoke, taurine, choline and the lipase enzyme for bile production and fat digestion.
• Targeted reflux support – If you regularly experience heartburn or reflux, consider increasing your stomach acid levels by ensuring adequate levels of vitamin B6, zinc and good hydration, whilst also working on reducing stress around meals. You can also supplement with betaine hydrochloride if diet lifestyle changes are not enough. Slippery elm can also be effective for reflux, stomach inflammation, and constipation. It is a rich source of soluble fibre acting as a prebiotic. The mucilage of slippery elm forms a slippery, viscous coating that soothes irritation in the throat and the lining of the stomach. It also stimulates the secretion of protective mucus.
• Support gut microbiome - Probiotic bacteria facilitate digestion and absorption of nutrients by producing digestive enzymes, promoting healthy gut lining, reducing pathogenic microbes, and promoting good motility. Include probiotic and prebiotic-rich foods daily. For example sauerkraut, kimchi, natural yoghurt or kefir, cruciferous and allium vegetables, and wholegrains.

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