How The Body Gets Energy – And Why Knowing Can Help You Lose Weight

If your body is getting it’s energy from the food you eat – well thats OK. But if it is burning the excess fat for energy – well that’s even better especially if you want to lose weight.

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The Digestive System

Here a quick resume about the two most misunderstood hormones that every dieter should know about.

Glucose is a simple sugar that provides energy to all of the cells in your body. Your cells then take in glucose from your blood and break it down for energy.

For instance, brain cells and red blood cells rely solely on glucose for fuel. The glucose in your blood comes from the food you eat.

When you eat, food gets metabolised via your intestines and is distributed through the bloodstream to the cells in your body.  In all conditions your body tries to keep the supply of glucose constant, maintaining as consistent as possible glucose concentration in the blood.  If it did not do this (as in diabetes for example) your cells would have too much glucose right after a meal (particularly a high carb one) and starve in between meals and during sleep.

When you have an excess of glucose, your body stores this in your liver and muscles by making glycogen,  long chains of glucose. Conversely, when glucose is in short supply, your body mobilizes glucose from stored glycogen and/or stimulates you to eat food.

To maintain this constant blood-glucose level, your body uses two hormones, insulin and glucagon, that are produced in your pancreas and have opposite actions.

Your pancreas is formed from clusters (Islets) of alpha and beta endocrine cells. The beta cells secret insulin and the alpha cells secret glucagons. Both these secretions are protein hormones made up of amino acids.

What insulin does

Insulin is used by almost all of your body’s cells, but it’s most active in the liver, fat and muscle cells. Insulin hasthe following effect:

– Inhibits the liver and kidney cells from making glucose from intermediate compounds of metabolic pathways (gluconeogenesis)

– Causes the liver and muscle cells to store glucose in glycogen

– Stimulates fat cells to form fats from fatty acids and glycerol

– Causes the liver and muscle cells to make proteins from amino acids Insulin production is the signal for the body to store energy (as fat).  It does so by reducing the concentrations of glucose, fatty acids and amino acids in the bloodstream.

insulin

Effect of insulin on glucose uptake and metabolism. Insulin binds to its receptor (1), which starts many protein activation cascades (2). These include translocation of Glut-4 transporter to the plasma membrane and influx of glucose (3), glycogen synthesis (4), glycolysis (5) and triglyceride (6).

What Glucagon does

Glucagon_rednblue

A microscopic image stained for glucagon

– Now when you don’t eat or eat low carb, your pancreas releases glucagons instead which causes your body to produce glucose.. Glucagon acts on the same cells as insulin but has the opposite effects

– Stimulates the liver and muscles to break down stored glycogen (glycogenolysis) and release the glucose

– Stimulates gluconeogenesis in the liver and kidneys

The action of glucagon is opposite to insulin in that glucagon mobilizes glucose stored inside your body and increases the level of glucose in your blood, thus stopping your blood glucose levels from falling dangerously low.

How insulin and glucagons work as a tag team

Under normal circumstances, the levels of insulin and glucagon are effectively counter balanced. When you eat, your body metabolises the food quite rapidly and registers the presence of glucose, fatty acids and amino acids absorbed from the food. This causes the pancreatic beta cells to release insulin into your blood and inhibit the pancreatic alpha cells from secreting glucagon.

As the levels of insulin in your blood begin to rise they act on the liver, fat and muscle cells in particular causing them to absorb the incoming molecules of glucose, fatty acids and amino acids. The insulin acts to prevent the concentration of glucose, fatty and amino acids from increasing too greatly in the bloodstream.

In this way, your body maintains a steady blood-glucose concentration. This action occurs when you eat a properly balanced diet as opposed to the high carb diet of today. Unfortunately, where the diet is high in carbs (or there is just too much food) it has to go somewhere and inevitably, that somewhere is as fat, just where you don’t want it.

Between meals, or when you are sleeping, your body senses that it is effectively starving. However your cells still need a supply of glucose to keep going. So while in this condition, the slight drops in blood-sugar level stimulate glucagon secretion from the alpha cells in the pancreas and in turn inhibit the release of insulin. Glucagon levels in the blood rise and start acting on liver, muscle and kidney cells to mobilize glucose from glycogen or to make glucose that’s released into your blood. Such action prevents the blood-glucose levels from falling too much.

This change occurs many times throughout the day with the secretion of either insulin or glucagons helping to keep your blood-glucose level relatively constant, typically in the range of 90 mg per 100 ml of blood.

The fluctuation of blood sugar (red) and the sugar-lowering hormone insulin (blue) in humans during the course of a day with three meals. One of the effects of a sugar-rich vs a starch-rich meal is highlighted.[1]

The fluctuation of blood sugar (red) and the sugar-lowering hormone insulin (blue) in humans during the course of a day with three meals. One of the effects of a sugar-rich vs a starch-rich meal is highlighted.

However, seeing as the secretion of the pancreas lag behind the blood glucose levels, the action of eating large quantities of high carb food will drastically disturb this. Simply put, when the blood glucose level is overly high more quantities of insulin will be produced than are needed as the glucose will have been dealt with. So more glucose will have been absorbed than was nessesary. This will cause a dip in the blood glucose level causing us to feel a lack of energy and trigger a production of glucagon.

Sunday Lunch Syndrome

full stomach photo by Eli Duke

This is something I call the “after Sunday lunch syndrome” as it is most often seen after a big meal. You will most likely have noticed that 30 – 60 minutes after eating far too much (as in a typical Sunday lunch) and then not moving a great deal either, you tend to feel really sleepy and quite soon many will also start to get the munchies and go looking for that last roast potato or piece of pie. In fact the body is wanting anything that will get the blood sugar up again – and so the cycle continues…

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