The digestion of macronutrients requires a great deal of enzymatic processes. When food is initially ingested salivary amylase begins the breakdown of carbohydrates. Lysosome is also contained within the saliva which has antibacterial properties. The food then travels to the stomach where is encounters a more acidic environment which also helps to kill off any unwanted microbes. It is here within the acidic environment that proteins begin to be broken down into smaller polypeptides prior to entering the duodenum.
To be able to be absorb B12 it needs to be bound to a carrier protein, known as R-binders or Transcobalamin 1. If it is in a free state this will occur within the saliva, or if released from protein it will bind within the stomach. The stomach also produces Intrinsic factor which is required for the B12 to be assimilated into the body, It is within the duodenum that B12 binds with Intrinsic factor. Lack of B12 may be due to a deficiency within the diet or an inability for it to be absorbed due to a lack of Intrinsic Factor.
Gastric acid is required to begin the process of the digestion of protein. Common signs and symptoms of low gastric activity include; bloating, belching, burning, and flatulence within 1 to 2 hours after meals, the sensation of fullness after eating, undigested food in the stools, and delayed protein breakdown. Other signs include foul smelling stools, chronic dysbiosis (candida, parasites, abnormal flora), indigestion, diarrhoea, constipation, Iron deficiency, multiple food allergies/sensitivities, nausea after taking medications, post adolescent acne, and week cracked fingernails. If experiencing such symptoms it may be worth considering Gastric acid supplements.
In the small intestine carbohydrates continue to be broken down into monosaccharides, and proteins into amino acids. Fats are broken down into monoglycerides, free fatty acid's, and cholesterol. Bile salts from the gallbladder aids in the digestion of lipids (fats), through emulsification, thereby breaking them down into smaller packages, called micelles. This facilitates Lipase to breakdown the lipids Ito monoglycerides and free fatty acids. These micelles will then disassociate allowing the monoglycerides and free fatty to be absorbed into the Enterocytes (intestinal absorptive cells). Any cholesterol contained within the micelles will also be absorbed. Most carbohydrates are easily absorbed when broken down into monosaccharides, however indigestible fibre is eliminated in the faeces.
Maldigestion can result in, gas, bloating, abdominal pain, and diarrhoea. Digestive bitters are an alternative to enzyme replacement. 10-20 drops are often taken in water before the meal for the bitter principal effect via the stimulation of the vagus nerve. These may included Swedish bitters or herbal extract formulas containing gentian, dandelion root or artichoke. Foods that also help to stimulate digestion are; Green leafy vegetables, Ginger, Turmeric, Fermented foods, Chia seeds, sweet potatoes can also aid digestion.
Low bile salts are associated with; constipation, fat malabsorption, steatorrhoea, floating stools, fatty food intolerance, gall stones, and nausea. Bile excretion needs water 6 to 8 glasses a day. Hydrochloric acid may increase bile production. Olive oil stimulates secretion. Choleretics, agents that stimulate the flow of bile into the duodenum include; dandelion root (Taxaxacum officinale), Silymarin (Silybum marianum), globe artichoke (cynara scolymus), Turmeric (curcuma longa).
The small intestines absorb the vitamins that occur naturally in foods, or in supplements. Fat-soluble vitamins A,D,E and K are absorbed along with dietary lipids. B12 is absorbed within the Ileum of the small intestines. However a high dairy diet can impair the absorption of B12. The gut microflora can also synthesise B12 but it is not known how much of this, if any, can be assimilated by the body. Microflora also produce about 50% of the Vitamin K used by the body.
Absorption generally occurs using three different processes; passive diffusion, mediated transport, and that involving carrier proteins which requires energy. Sodium plays an important role in supporting the absorption of monosaccharides and amino acids, and once absorbed they are then transported to the liver and then delivered to the rest of the body. Nucleotides are also absorbed and transported to he liver. Nucleotides are found in a variety of foods, except fruit.
Short-chain fatty acids are relatively water-soluble and can be absorbed directly. However large long chain fatty acids are enclosed within micelles. This process enables the fatty acids to be broken down into smaller packages and thereby help with their absorption. They are then combined again within the enterocytes to form triglycerides. These are packaged into particles called chylomicrons. The Chylomicrons are then transported into the lymphatic vessels and eventually into the bloodstream. Once in the bloodstream the enzyme lipoprotein lipase contained in the cell walls of adipose and muscle cells, break down the triglycerides into free fats acids and glycerol. These breakdown products then passed through cell walls to be used for energy by muscle cells or stored in adipose tissue. Any excess are carried to the liver.
Absorbed Glucose first enters the liver; some is used to make ATP (the energy currency of the body), the excess is converted to glycogen (the storage form of glucose), and the remainder to form Fatty Acids. Together with any excess triglycerides are then packaged to form VLDL (very low density lipoproteins) these will also contain cholesterol and delivered through the blood where the triglycerides will be stored in adipose tissue or used for energy. Removal of the triglycerides will result in the production of an IDL (immediate density lipoprotein) which will travel to the liver. Through the action of the liver any remaining triglycerides will be removed, resulting in the formation of LDL (low density lipoproteins) which contains mostly cholesterol. These are then released into the bloodstream. Once attached to cells the cholesterol is taken up and used to form; plasma membranes, the myelin sheath around neurones, and for the synthesis of steroid hormones (cortisol, aldosterone, oestrogen and testosterone). Any excess cholesterol is removed from the cell and eventually forms HDL (high density lipoprotein) which delivers the excess cholesterol back to the liver, where it is used to form bile.
Plant foods also contains an undigestible component which is referred to as Dietary Fibre. It has two forms, Soluble, which dissolves in water and Insoluble, which does not. Both have beneficial effects towards health. Together they help remove excess cholesterol from the body, control blood glucose levels, decreases constipation and thereby reducing the risk of developing haemorrhoids, and colorectal cancer. High fibre foods tend to be more filling than low fire foods thereby helping to control body weight. Increasing the amount of plant based foods into the diet will naturally increase the amount of fibre ingested.
Also important to health is intestinal flora which acts symbiotically within the body. They play an important role in gut health and also have a positive effect upon the immune system. Half of our daily requirement of Vitamin K is produced within the gut flora. They also synthesis Thiamine, folic acid, Biotin, Riboflavin and Pantothenic acid, and Vitamin B12. Many of these vitamins are already within our diet, and as has already been mentioned it is unclear whether the body is able to the utilise the B12 produced within the gut flora.
Microflora also produce SCFA (short-chained fatty acids) which are believed to be beneficial for cognition and emotion, have anti-inflammatory properties, and are preventative of certain cancers, in particular colon cancer. They are also beneficial in controlling blood-sugar levels. Prebiotics help to promote the growth of healthy bacteria and can be obtained from; artichokes, asparagus, bananas, Barley, berries, chicory, garlic, green vegetables, legumes, oats, onions, soybeans, and wheat.
There are many conditions that have been associated with problems of increased gut permeability, for example; inflammatory bowel disease, Crohn's disease, food allergy and coeliac disease.
The 4R program has demonstrated to be effective in treating problems of poor assimilation issues. This involves
- Removing factors that contribute to the situation, for example; Stress, certain hyper-allergic foods, and pathogens.
- Replacing with the necessary digestive enzymes and hydrochloric acid.
- Reinoculating with the beneficial bacteria, and prebiotics to support.
- Repair by reducing any inflammation present and supporting cells growth; Omega 3 fatty acid, zinc, Vitamin B5 and Vitamin D are used as supporting supplements.
Control of Eating
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