BEFORE DISCUSSING INSULIN, we must understand hormones in general. Hormones are molecules that deliver messages to a target cell. For example, thyroid hormone delivers a message to cells in the thyroid gland to increase its activity. Insulin delivers the message to most human cells to take glucose out of the blood to use for energy.
To deliver this message, hormones must attach to the target cell by binding to receptors on the cell surface, much like a lock and key. Insulin acts on the insulin receptor to bring glucose into the cell. Insulin is the key and fits snugly into the lock (the receptor). The door opens and glucose enters. All hormones work in roughly the same fashion.
When we eat, foods are broken down in the stomach and small intestine. Proteins are broken into amino acids. Fats are broken into fatty acids. Carbohydrates, which are chains of sugars, are broken into smaller sugars. Dietary fiber is not broken down; it moves through us without being absorbed.All cells in the body can use blood sugar (glucose). Certain foods, particularly refined carbohydrates,raise blood sugar more than other foods. The rise in blood sugar stimulates insulin release.
Protein raises insulin levels as well, although its effect on blood sugars is minimal. Dietary fats, on the other hand, tend to raise both blood sugars and insulin levels minimally. Insulin is then broken down and rapidly cleared from the blood with a half-life of only two to three minutes.
Insulin is a key regulator of energy metabolism, and it is one of the fundamental hormones that promote fat accumulation and storage. Insulin facilitates the uptake of glucose into cells for energy.
Without sufficient insulin, glucose builds up in the bloodstream. Type 1 diabetes results from the autoimmune destruction of the insulin-producing cells in the pancreas, which results in extremely low levels of insulin. The discovery of insulin (for which Frederick Banting and J.J.R. Macleod were awarded the 1923 Nobel Prize in Medicine), changed this formerly fatal disease into a chronic one.
At mealtimes, ingested carbohydrate leads to more glucose being available than needed. Insulin helps move this flood of glucose out of the bloodstream into storage for later use. We store this glucose by turning it into glycogen in the liver—a process is called glycogenesis. (Genesis means “the creation of,” so this term means the creation of glycogen.) Glucose molecules are strung together in long chains to form glycogen. Insulin is the main stimulus of glycogenesis. We can convert glucose to glycogen and back again quite easily.
But the liver has only limited storage space for glycogen. Once full, excess carbohydrates will be turned into fat—a process called de novo lipogenesis. (De novo means “from new.” Lipogenesis means “making new fat.” De novo lipogenesis means “to make new fat.”).
Several hours after a meal, blood sugars and insulin levels start to drop. Less glucose is available for use by the muscles, the brain and other organs. The liver starts to break down glycogen into glucose to release it into general circulation for energy—the glycogen-storage process in reverse.
This happens most nights, assuming you don’t eat at night.
Glycogen is easily available, but in limited supply. During a short-term fast (“fast” meaning that you do not eat), your body has enough glycogen available to function. During a prolonged fast, your body can make new glucose from its fat stores—a process called gluconeogenesis (the “making of new sugar”). Fat is burned to release energy, which is then sent out to the body—the fat-storage process in reverse.
Insulin is a storage hormone. Ample intake of food leads to insulin release. Insulin then turns on storage of sugar and fat. When there is no intake of food, insulin levels fall, and burning of sugar and fatis turned on.
This process happens every day. Normally, this well-designed, balanced system keeps itself in check. We eat, insulin goes up, and we store energy as glycogen and fat. We fast, insulin goes down and we use our stored energy. As long as our feeding and fasting periods are balanced, this system also remains balanced. If we eat breakfast at 7 a.m. and finish eating dinner at 7 p.m., the twelve hours of feeding balances the twelve hours of fasting.
Glycogen is like your wallet. Money goes in and out constantly. The wallet is easily accessible, but can only hold a limited amount of money. Fat, however, is like the money in your bank account. It is harder to access that money, but there is an unlimited storage space for energy there in your account. Like the wallet, glycogen is quickly able to provide glucose to the body. However, the supply of glycogen is limited. Like the bank account,fat stores contain an unlimited amount of energy, but they are harder to access.
This situation, of course, partially explains the difficulty in losing accumulated fat. Before getting money from the bank, you spend what’s in your wallet first. But you don’t like having an empty wallet. In the same manner, before getting energy from the Fat Bank, you spend the energy in the Glycogen Wallet. But you also don’t like an empty Glycogen Wallet. So you keep the Glycogen Wallet filled, which prevents you from accessing the Fat Bank. In other words, before you can even begin to burn fat, you start feeling hungry and anxious because your glycogen is becoming depleted. If you continually refill your glycogen stores, you never need to use your fat stores for energy.
What happens to the excess fat that is produced through de novo lipogenesis? This newly synthesized fat can be stored as visceral fat (around organs), as subcutaneous fat (underneath the skin) or in the liver.
>Under normal conditions, high insulin levels encourage sugar and fat storage. Low insulin levels encourage glycogen and fat burning. Sustained levels of excessive insulin will tend to increase fat storage. An imbalance between the feeding and fasting will lead to increased insulin, which causes increased fat, and voilà—obesity.
Source: D.R Jason fung”book:the obesity code –unlocking the secrets of weight loss”