Fasted vs Overfed State
“How our body responds to a calorie deficit is largely dependent on our hormonal state. Your body is more concerned about avoiding a blood sugar crash than it is about maintaining muscle mass. That’s why during fasting we tend to convert large amounts of amino acids into glucose, which is stored in the liver as glycogen and then released to maintain blood glucose levels. Hormone status and the presence of ketones can change how much protein we convert to glucose. The reason why our bodies still need glucose is because tissues, like red blood cells and certain parts of the brain, can only run on glucose. Instead of the body breaking down amino acids into glucose (gluconeogenesis), the body uses stored body fat as fuel. As the body shifts to fat as a primary fuel source, a by-product of fat metabolism begins to accumulate: ketones. The metabolic state of “ketosis” is normal and almost as old as time. Ketones are like small pieces of fat that are water-soluble, and given a few days or weeks, most of our tissues can shift their metabolism to burn ketones. The shift to ketosis solves two very important problems:
- It protects scarce blood glucose by shifting as much of our metabolic machinery as possible to a nearly limitless fuel supply. We have a day or two of liver glycogen, but even if we are relatively lean, we have months of stored body fat. A shift to ketosis saves scarce glycogen to be used to maintain minimal blood glucose levels.
- Ketosis halts gluconeogenesis. This spares muscle mass that would be very valuable in a state of prolonged starvation. In addition to blocking gluconeogenesis from amino acids, ketosis provides a sneaky alternative way to make glucose using the glycerol backbone of fats.
Being a fat burner can help improve caloric efficiency, which means you need less calories to do the same job; thriving on fewer calories. As a result, this slows the rate of cell division and enhances cell repair. It optimizes the flow of testosterone and growth hormone in the bloodstream. It improves immune function. Whereas, increased caloric consumption speeds up cell growth and division.
However, if we are overfed our brain no longer hears the fullness signal from leptin. When we are overfed on carbs, our liver and muscle glycogen are filled, but we still have excess free glucose in the bloodstream. Excess carbs are then converted to fat in the form of a short-chain saturated fat called palmitic acid. This palmitic acid is stitched to the glycerol molecule and packaged with proteins and cholesterol and the resultant molecule is called a VLDL. Palmitic acid has a very potent effect on our metabolism and our hormonal environment in that it decreases our sensitivity to leptin. Palmitic acid that causes the leptin resistance in the brain leads to our inability to feel full, and is made from excess dietary carbs. Once we develop insulin sensitivity, the inhibitory systems in the liver are overwhelmed and blood glucose is converted into fats and VLDLs at such a high rate that escape into circulation and begin to accumulate in the liver. This is the beginning of non-alcoholic fatty liver disease (Paleo Solution, 69)”. “Overeating can lead to mitochondrial damage. Mitochondria are tiny organelles found in most cells and are responsible for the process of converting the basic molecular constituents of food into energy. As a result, this process produces waste products – in the case of overeating, free radicals, which can be harmful if not well controlled. The damage created by the overfed state can impair our ability to use fat as a fuel source (Wired to eat, 54)’