Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed  into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones.

When food enters the mouth, its digestion starts by the action of mastication, a form of mechanical digestion, and the contact of saliva. Saliva, which is secreted by the salivary glands, contains salivary amylase, an enzyme which starts the digestion of starch in the food. After undergoing mastication and starch digestion, the food will now be in the form of a small, round mass, called a bolus. It will then travel down the esophagus and into the stomach by the action of peristalsis. Gastric juice in the stomach starts protein digestion. Gastric juice mainly contains hydrochloric acid and pepsin. As these two chemicals may damage the stomach wall, mucus is secreted by the stomach, providing a slimy layer that acts as a shield against the damaging effects of the chemicals. At the same time protein digestion is occurring, mechanical mixing occurs by peristalsis, which are waves of muscular contractions that move along the stomach wall. This allows the mass of food to further mix with the digestive enzymes. After some time (typically an hour or two in humans, 4–6 hours in dogs, somewhat shorter duration in house cats), the resulting thick liquid is called chyme. When the pyloric sphincter valve opens, chyme enters the duodenum where it mixes with digestive enzymes from the pancreas, and then passes through the small intestine, in which digestion continues. When the chyme is fully digested, it is absorbed into the blood. 95% of absorption of nutrients occurs in the small intestine. Water and minerals are reabsorbed back into the blood in the colon (large intestine). Some vitamins, such as biotin and vitamin K (K2MK7) produced by bacteria in the colon are also absorbed into the blood in the colon. Waste material is eliminated during defecation.

Digestive systems take many forms. There is a fundamental distinction between internal and external digestion. External digestion is more primitive, and most fungi still rely on it. In this process, enzymes are secreted into the environment surrounding the organism, where they break down an organic material, and some of the products diffuse back to the organism. Later, animals form a tube in which internal digestion occurs, which is more efficient because more of the broken down products can be captured, and the internal chemical environment can be more efficiently controlled.

Protein digestiochymotrypsin

Protein digestion occurs in the stomach and duodenum  in which 3 main enzymes, pepsin secreted by the stomach and trypsin and chymotrypsin secreted by the pancreas, break down food proteins into polypeptides that are then broken down by various exopeptidases and dipeptidases into amino acids. The digestive enzymes however are mostly secreted as their inactive precursors, the zymogens. For example, trypsin is secreted by pancreas in the form of trypsinogen, which is activated in the duodenum by enterokinase to form trypsin. Trypsin then cleaves proteins to smaller polypeptides.

Fat digestion

Digestion of some fats can begin in the mouth where lingual lipase breaks down some short chain lipids into diglycerides  The presence of fat in the small intestine produces hormones that stimulate the release of pancreatic lipase  from the pancreas and bile from the liver for breakdown of fats into fatty acids. Complete digestion of one molecule of fat (a triglyceride) results in 3 fatty acid molecules and oneglyserol molecule.

Carbohydrate digestion

In humans, dietary starches are composed of glucose units arranged in long chains called amylose, a polysaccharide. During digestion, bonds between glucose molecules are broken by salivary and pancreatic amylase, resulting in progressively smaller chains of glucose. This results in simple sugars glucose and maltose (2 glucose molecules) that can be absorbed by the small intestine.

Lactase is an enzyme that breaks down the disaccharide lactose  to its component parts, glucose and galactose. Glucose and galactose can be absorbed by the small intestine. Approximately half of the adult population produce only small amounts of lactase and are unable to eat milk-based foods. This is commonly known as lactose intolerance.

Sucrace is an enzyme that breaks down the disaccharide sucrose, commonly known as table sugar, cane sugar, or beet sugar. Sucrose digestion yields the sugars fructose and glucose which are readily absorbed by the small intestine.

Digestive hormones

Action of the major digestive hormones

There are at least five hormones that aid and regulate the digestive system in mammals. There are variations across the vertebrates, as for instance in birds. Arrangements are complex and additional details are regularly discovered. For instance, more connections to metabolic control (largely the glucose-insulin system) have been uncovered in recent years.

  • Gastrin – is in the stomach and stimulates the gastric glands to secrete pepsinogen (an inactive form of the enzyme pepsin) and hydrochloric acid. Secretion of gastrin is stimulated by food arriving in stomach. The secretion is inhibited by low pH.
  • Secretin – is in the duodenum and signals the secretion of sodium bicarbonate in the pancreas and it stimulates the bile secretion in the liver. This hormone responds to the acidity of the chyme.
  • Cholecystokinin (CCK) – is in the duodenum and stimulates the release of digestive enzymes in the pancreas and stimulates the emptying of bile in the gall bladder. This hormone is secreted in response to fat in chyme.
  • Gastric inhibitory peptide (GIP) – is in the duodenum and decreases the stomach churning in turn slowing the emptying in the stomach. Another function is to induce insulin secretion.
  • Motilin – is in the duodenum and increases the migrating myoelectric complex  component of gastrointestinal motility and stimulates the production of pepsin.

Significance of pH in digestion

Digestion is a complex process controlled by several factors. pH plays a crucial role in a normally functioning digestive tract. In the mouth, pharynx, and esophagus, pH is typically about 6.8, very weakly acidic. Saliva controls pH in this region of the digestive tract.Salivary amylase  is contained in saliva and starts the breakdown of carbohydrates intomonosaccharides . Most digestive enzymes are sensitive to pH and will denature in a high or low pH environment.

The stomach’s high acidity inhibits the breakdown of carbohydrates within it. This acidity confers two benefits: it denatures proteins for further digestion in the small intestines, and provides non-specific immunity,  damaging or eliminating various pathogens.

In the small intestines, the duodenum provides critical pH balancing to activate digestive enzymes. The liver secretes bile into the duodenum to neutralize the acidic conditions from the stomach, and the pancreatic duct empties into the duodenum, adding bicarbonate to neutralize the acidic chyme, thus creating of neutral environment. The mucosal tissue of the small intestines is alkaline with a pH of about 8.5.

  • Eat food. May sound obvious, but by food I mean substances that your body recognises and knows what to do with. The problem with most artificial ingredients, from hydrogenated fat to artificial colours is that our bodies don’t know what they are, and can’t break them down. They are like unwanted Christmas presents from your family – you don’t know what to do with them, but can’t throw them away.
  • Take probiotics. We think we digest our own food – actually is the bacteria living in our guts that do most of it for us, and if they are not happy, we don’t get fed.
  • Don’t eat too much. It takes 20 minutes for our stomach to realise it is full, so by the time that happens we are usually very full. Always leave yourself wanting more.
  • Establish regular habits. Don’t be coy, we are all friends, we can talk about poo without blushing. You can’t digest food properly if everything is happening too fast or too slow. If you are not as regular as you would like, have a quiet conversation with your health & bodycare team – I am sure they would love to help. For some gentle assistance, try psyllium husks or ground flax seeds in water.
  • Chew on some seeds. Have you ever been for an Indian meal, and been given a bowl of multi-coloured seeds at the end? Not been entirely sure what to do with them? They would have been a mixture of fennel, aniseeds and other aromatic seeds which can help digestion when chewed after eating. If you don’t fancy munching on seeds, a cup of fennel tea after a meal will do the same thing.
  • Get some bitterness. The only bitters most of us consume are beers, but that is not what I am talking about here. If you suffer from indigestion, and particularly have difficulty with high fat foods, try some bitters before eating. Anything bitter will stimulate appetite, and gets your stomach and liver producing bile and digestive juices in readiness for eating. A few drops of a dandelion root extract in water will do the job nicely.
  • Eat fibre. But avoid bran. Fibre is essential for pushing other foods through your gut, and evening out the flow. Grains like oats and brown rice are very high in soluble fibre, as are fruits and vegetables. Bran on the other hand is insoluble fibre, making it scratchier on the inside, and it can also reduce the absorption of essential minerals. Porridge not All Bran, that’s the message.
  • Drink water. Without thinking about this too much, do you want you intestines to be moist and soft, or dried and scratchy?
  • See last weeks Ask Al, and do a detox every now and then. I am sure you need regular holidays – a detox is like a holiday for your bowels.
  • If you have followed all of these, you shouldn’t need number 10.

Having suffered myself over the years with undiagnosed issues with my digestion I decided to look into it myself. It’s amazing, the human body and just how much we throw at ourselves to deal with on a day to day basis without even realising. Your digestion is a key part of your bodies evolution, without nurturing yourself in the right way (with the right amount of minerals, vitamins and fats) we can seriously unbalance this ballet of bacteria and enzymes that sustain our delicate internal eco system.

This blog doesn’t just cover the spiritual but the practical of sustenance for your bodies needs. Also take into account that along the way you need for specific portions of food will change depending on season and your health at any given time. Over feeding can cause subtle problems as well as under feeding, give your body a fighting chance to work at its optimum by listening to what it needs. Your body is actually very clever and will give you hints as to what it may need and be lacking.  It is also important to take into account, the body can give a signal of being hungry when in fact it’s trying to communicate thirst. Please see my input on water in this blog.

Happy eating!

My Eden Project

Information supplied by Wiki & Planet Organic Website