So I will begin with the “fed” state and address the “fasted” state in another blog in the next few days. I hope that in presenting this basic information people will hopefully gain a clearer perspective of how our bodies utilise and store the food we eat. I have to admit that I have heard some pretty crazy things said on various media platforms in regards to the ‘right’ way of eating, and I think with some basic understanding of what is occurring in our bodies we will together be better equipped to recognise the ‘crazy’ from the plausible.
The “Fed State” is a time of storage and is the basic physiological processes that occurs once we have just consumed food or drink. Essentially, once the consumed food makes its way from the mouth to the oesophagus and into the stomach it is broken down and transferred to the small intestine. Thus we will focus our attention on the duodenum of the small intestine, as it is here that our macromolecules are absorbed and transported to the various organs and tissues. So, the products of digestion are monosaccharides or simple sugars such as glucose, amino acids as the building blocks that construct proteins, and fatty acids as the building blocks that form triglycerides (along with a glycerol backbone). If we observe the important organs involved in the “fed” state we find the said duodenum, the all-important liver, the pancreas and the blood stream.
So as stated, once the food (chyme) has made its way to the absorptive epithelial cells of the duodenum, our blood glucose levels rise. This rise in blood glucose levels combines with the parasympathetic nerve innervation that triggers the pancreatic beta cells of the islets of langerhans to produce and release insulin. Now, insulin initiates a cascade of events that ultimately results in the uptake of glucose by organs and tissues. Notably, the liver uptakes glucose from the blood stream and tends to store glucose as glycogen. The liver does this as it wants to store glucose in a form (glycogen) that it can draw on as necessary in times of high metabolic demand. Glucose in the liver can also be converted into pyruvate and it is this conversion process that generates adenosine triphosphate (ATP), which essentially powers the body. Pyruvate can further convert into acetyl-coA which then enters the Krebs cycle (occurs in mitochondria) and results in the production of more ATP (energy). Interestingly enough, acetyl-coA can also produce fatty acids, which then go on to form triglycerides. The Liver then packages up these triglycerides into transportable lipoproteins which are then able to travel in the blood stream to adipocytes to be stored.
Now above is what occurs to glucose taken up by the liver, however, glucose can be taken up by adipose tissue (fat tissue) and can be converted to acetyl-coA and ultimately stored as a rich energy source (triglycerides). Glucose can also be taken up by skeletal muscle and used to create ATP (energy) or alternatively stored as glycogen ready for future use. Very importantly, the brain uses a vast amount of glucose as it is its main source of energy and the subsequent conversion of glucose to ATP powers brain function and activity.
So above we have covered the basics of what occurs to glucose under the influence of the hormone insulin in the “fed” state. However it is important to mention the other macromolecules, such as amino acids. Amino acids are the building blocks of proteins, thus these too are taken up by the liver and essentially used to build the various proteins needed for homeostasis. Fatty Acids are the other macromolecule and interestingly these take a different path then glucose & amino acids, fatty acids are transported as chylomicrons from the epithelial cells of the duodenum to the lacteal (lymphatic) capillaries. It is from the lymphatic system that they eventually enter the blood stream and are too up taken into the liver where they are packaged as lipoproteins and sent via the blood stream to adipose tissues to be stored as triglycerides, or they are taken directly to the heart as this amazing muscle uses fatty acids and its subsequent conversion to ATP as its main source of fuel.
As stated all the above processes are initiated by the hormone insulin, secreted by the pancreas. Thus to recap the effects of insulin, it stimulates the uptake of glucose & amino acids to the liver, it decreases glycogenolysis, it stimulates the uptake of glucose to adipocytes, stimulates the uptake of glucose and the production of glycogen in skeletal muscle, stimulates glycogen production in the liver & glycolysis. Thus the “fed” state is all about glycogenesis (converting glucose to glycogen), glycolysis (breakdown of glucose to form ATP), Lipogenesis and protein synthesis.
I hope the above information describing the “fed” state has highlighted the importance of the three macromolecules (Carbs, Fats, Protein) and shows that we have physiological processes which require a diet that contains, in varying amounts, all three of these essential components. I encourage everyone to enjoy your food, eat in moderation, and as a general rule of thumb stay away from overly processed and packaged foods. Yet most importantly, listen to your body.
As always feel free to contact me with any questions you may have.
Giancarlo Nerini – Licensed Acupuncturist