Okay, so back to the drawing board. If it's not the fat, then what is it? Protein has remained the same for several decades, so let's look at the next macro-nutrient group, carbohydrates. As we discussed previously, people starting eating less fat and more carbohydrates in the form of cereals after the introduction of the food pyramid in the 1970s. More startlingly is the higher consumption of high fructose corn syrup. Completely unknown prior to 1980, we now make 17.5 billion pounds of it and consume 66 pounds per person every year. It's a more potent form of sugar that increases appetite, promotes obesity, and leads to diabetes and an inflamed brain. It is the main form of sweetener in all processed food from soft drinks to turkey slices. Recall what happens when you eat a mixed meal made up of protein, carbohydrates, and fat. Proteins get broken down into amino acids, they're building blocks, carbohydrates into sugar or glucose, and fats are turned into their building blocks, fatty acids. These get broken down further into acetyl CoA which is a universal currency of energetic substrate in the cell.
Acetyl CoA then gets processed into the Kreb's cycle, also called the citric acid cycle to make ATP or the pure form of energy that can be used by the cell for various functions. When all goes well, the consumption of carbohydrates into a lesser degree protein results in the secretion of insulin by your pancreas. Insulin is an important hormone widely known for its effect on glucose, but it has many more function. Insulin secretion act as an energy switch. It tells your body that it is in a fed state and needs to use the readily available energy source coming from food for its immediate needs and to store energy.
Insulin makes different cells in your body take up that glucose by binding to its special receptors. Most of the sugar is taken up by the muscle cells, but other cells also take up that sugar, like the liver, the fat, and other organs.
It also tells your fat stores to stop releasing fatty acids for energy since you already have readily available glucose to use. It inhibits what we call lipolysis or the breakdown of fat. It tells your liver to stock up on sugar in the form of glycogen.
In addition to its role in uptake of sugars, insulin also has a role in retention in sodium and hence water by the kidneys. All of this happens in normal conditions. Insulin and its receptor work like a key and lock model. Insulin fits in the lock or its receptor, this opens specialized channels for sugars to get in the cell.
In the past, we thought that the lock was defective and that insulin couldn't open those channels in the cell, which caused sugar to float around in the blood outside the cell and basically caused high sugar that resulted in diabetes.
We now know that this is not the case. Insulin and it's receptor are functioning just fine, but there is too much sugar in the cell because too much is being eaten in the form of carbohydrates or too often a combination of both. So insulin is working hard to cram all that glucose in the cell but the cell is just too full. The pancreas senses all the glucose floating around and starts pumping out more and more insulin which elevates the amount of insulin in the blood. The body's trying to use up all that energy so it stores it as glycogen in the liver and muscles and start storing it as fact or what is called denovo lipogenesis, meaning that the carbs you're eating are turning into fat. The fat cells starts storing fat and get bigger and bigger. They don't multiply to accommodate that excess fat. Once the fat cells get too big, fat starts depositing in other organs outside of the fat tissue. We call this ectopic fat deposition, and it starts in your liver, which is what causes fatty liver, a very dangerous condition that can lead to liver failure if not addressed. It also deposits in your blood vessels and elsewhere. This growing fat mass causes the immune system to activate. This is the inflammatory response and that is what is behind the inflammation and clogging of your blood vessels.
That balance between your vessels constricting and dilating is also lost and the inflamed blood vessels start signaling your platelets to come and heal the inflammation. And this is how plaque starts forming in the blood vessels.
This is insulin resistance. It is what happens, 10 or even 20 years before your body even shows any signs of diabetes. And once diabetes developed, you are already behind. Until the 1970's we thought the brain was the one organ in the body not sensitive to insulin. It turns out insulin is not only essential for metabolism in the brain but it has other roles including promoting the formation of U cells or neurogenesis.
It inhibits apoptosis or neuronal cell death, it plays a key role in the balance between long term potentiation and depression which are important mechanisms in learning and memory. It modulates inflammatory responses in the glial cells and it promotes dilation of blood vessels in the brain that causes enhanced cerebral profusion. Ultimately, insulin is a critical hormone in the brain.